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Warm again today; quite a bit cooler tomorrow
You don't need a Weather Geek to tell you it's downright balmy outside.
The Redding Airport reported 75 degrees just before 1 p.m. That's already a few degrees above the max temp I predicted, going out on a bit of a limb. Most of the pros said we'd barely break 70 degrees today.
We can thank the north wind for cranking up temperatures. Winds blowing through the night churned the air, keeping early morning lows from falling below 50 degrees in many spots and giving us quite a head start on the day's warming.
These winds are still huffing and puffing as we head into afternoon, gusting to 22 mph and bringing a San Gabriel-esque warmth to the far northern valley.
That's because the winds are blowing down slope, warming with compression the way any gas does when you cram more of it into a smaller space. I would not be surprised to see temps approach 80 degrees thanks to these winds, even though I expect them to die down as the afternoon goes on.
It's the usual story -- high pressure to the north in the wake of yesterday's weak front has sent winds tumbling down the valley.
But the gradient will switch directions tomorrow as a trough approaches the west coast. We can expect much cooler afternoon temps -- maybe mid-60s tops, as clouds increase, sluggish up-valley flow takes over and a flood of cooler air aloft mixes to the surface.
I was never impressed with this front as a potential valley rain and mountain snow maker, and I remain bearish. But I won't rule out showers for the northern valley and snow for the surrounding mountains -- possibly into the upper-foothills, following the swamp cooler effect so prominent this season -- starting late tomorrow night into Saturday morning. Rain and snow will generally be heavier the farther north and west you go.
I still expect north winds to gin up again Sunday and blow into Wednesday as we sit under a northwest flow. But these winds won't be as warm as those we're getting today.
Longer-range forecasts continue to suggest a wet pattern returning around March 8. No way to pin that down till we're closer.
Posted by Bert Blanton at March 4, 2008 8:23 AM
Hello Scott, I own and operate the Bert Blanton School of Flight at Redding Municipal, and also teach aviation at Shasta College. Much of this class is meteorology, of which I have a decent knowledge and background. My question for you is: Since the Earth is a nearly perfect sphere, why are sunrise and sunset variences not linear? Ie, shouldn't the rising/setting times be one minute different each day?
Thanx for any enlightenment you may offer! Bert
p s, please reply to my e-mail address.
Another nice day -- maybe a scosche cooler (update: it's actually warmer)
Rest of today
67 degrees
Sunshine occasionally filtered through high and middle clouds
North to east wind to 6 mph
Sunshine sometimes filtered through high clouds
North wind to 15 mph, easing afternoon
Rest of this week: Friday looks nice; slim shower chances Saturday
Friday looks like another mild early-spring type day with afternoon temps again approaching 70s degrees.
Mid-range forecasts still show maritime polar air bursting through to the Pacific Northwest late Friday into Saturday. It's still possible the bottom of this big cold air pouch could push clouds and even spawn a few showers over the far northern Sac Valley before it moves through later Saturday.
It's possible this front could wind up a bit more vigorous than forecasts show now. We'll see.
Next week: Bright and breezy to start, then calm and warm
Gusty north winds still look like a good bet starting Sunday as the cold air pushes into the Great Basin while a fairly steep ridge builds off the west coast in its wake. These winds could crank up later Saturday and may blow through the middle of next week.
These winds could die down by Thursday as high pressure off the coast finally spreads warm air east, relaxing the gradient.
The long-range GFS (Global Forecast System) has backed off a bit on the idea of strong polar westerlies mowing down the ridge later in the week, ushering in a wet pattern. The waves look weaker in more recent runs, and less likely to dig south.
I'm sure everyone will be monitoring this potential pattern change.
Discussion of today's forecast
Thickening high clouds capped yesterday's temps before they could hit 70 degrees (the Redding Airport high was 68 degrees). We've got more high clouds today, along with slightly cooler air aloft sliding in this afternoon as a wave dimples the west coast ridge.
So I went with slightly cooler afternoon temps for today.
This 11:15 a.m. satellite image shows the high clouds streaming across northern California:
I analyzed the flows creating this pattern on this 11:15 a.m. satellite water vapor image:
1. 80-knot jet on the front side of a shallow trough off the west coast. This trough -- a big bag of cold air, essentially -- will dilute the ridge (a big bulge of warm air) as the day goes on.
2. Moisture riding up along the ridge/trough boundary from the southwest, bringing high clouds to our skies.
Time is short today, and that's all I've got.
Update 3:21 p.m.
Despite the continued cloud cover, we're getting the balmy weather today some of us predicted for yesterday. The Redding Airport hit 70 degrees just before 3 p.m. and could go a couple degrees higher. No one forecast such warm temps.
I've seen this phenomenon before, where an incoming trough on the back side of a ridge leads to warmer-than-expected temps as southwest flow wafts in warmer air. Of course, whenever I try to bump up expected temps with this phenomenon in mind, it never pans out.
Pretty nice
Rest of today
70 degrees
Fair with occasional high clouds
North wind to 8 mph
Sunshine filtered through high clouds
North wind to 8 mph
Rest of this week: Mostly sunny and through Friday; slight chance of showers Saturday
Mid-range forecasts show a ridge (warmish, sinking air) holding over northern California Thursday and Friday for more proto-spring weather -- cool morning and mild, blossom-perfumed afternoons.
Cooler air surging out of the Gulf of Alaska toward the Pacific Northwest starts to dilute the ridge by late Friday, much the way running a cold tap into a hot bath will drop the water temperature.
Forecasts suggest the front at the leading-edge of this latest cold air invasion could push far enough southeast to spread clouds and even some showers into the northern valley by Saturday morning. I'm not convinced this will happen yet, though forecasts do seem to be growing a bit more bullish on the idea.
Next week: Bright and breezy, followed by possible wet pattern return
Gusty north winds look like a better bet than any rain or snow from Saturday's front. These winds could crank up later Saturday and may huff and puff through the middle of next week as strong high pressure builds at the surface and aloft over the Pacific Northwest.
These winds could die down by Thursday as high pressure off the coast finally spreads warm air east, relaxing the gradient.
The long-range GFS (Global Forecast System) suggests polar westerlies may mow down the ridge later next week, opening the way for a whole series of wet waves toward mid March.
This potential pattern change isn't a sure thing, since it's way beyond the realm of forecast reliability. But it's certainly worth watching.
Discussion of today's forecast
Temperatures are rising nicely today after dropping to unexpected (for me, anyway) depths this morning, into the mid-30s.
I analyzed the pattern giving us an early taste of spring on this 11:45 a.m. satellite water vapor image:
1. Rather deep (978 mb at the surface) low over the Gulf of Alaska is helping push up the ridge down stream, over us. This low, however, is moving faster than the ridge, and will eventually ride over it, flattening it and diluting it by tomorrow. Moisture from this low and its trailing frontal system will likely spread more high clouds through north state skies tomorrow.
2. The ridge. This is an area of clockwise flow, where air at the surface tends to rotate out from a center of high pressure, causing air aloft to sink toward the surface to take its place. Sinking air generally warms and dries adiabatically (through compression).
Clockwise flow within the ridge is pulling some cirrus over the north state today. But these high clouds aren't really thick enough to slow insolation.
Here's how the GFS models the pressure patterns aloft and at the surface as of 4 p.m. today:
That arch of warm color contours over California tells you everything you need to know about today's weather. The yellow-orange over the north state represents 500 mb heights in the 576-to-582-decameter range, which is well above normal for this time of year (remember 500 mb heights are proportional to air mass warmth, since warmer air is more expansive than colder air).
The widely-spaced black isobars, or lines of equal surface pressure, suggest continued light winds.
Bottom line: My forecast high of 70 degrees might have been a bit too conservative.
Update: 4:56 p.m.
It looks like thickening high clouds blunted the sunshine afterall. Redding Airport temps have been stuck at 67 degrees all afternoon after rising smartly through the morning. I very much doubt the airport hit the predicted mark.
Rain check: storm total, February and season to date
Storm total
Here are preliminary Feb. 23-24 precipitation totals for selected north state spots courtesy of the California Department of Water Resources, the National Weather Service and the Citizen Weather Observer Program. Totals are in inches:
Brandy Creek: 7.76
Summit City (Shasta Lake): 3.52
Shasta Dam: 3.24
Fire Station 2 (west Redding): 2.28
Girvan Road area (southwest Redding): 1.77
Mount Shasta: 1.75
Upper Hilltop (north-central Redding): 1.57
Deschutes and Swede Creek (Palo Cedro): 1.56
Victor and Derby (Enterprise): 1.62
Hacienda Heights (northeast Redding): 1.37
Hillcrest (Hatchet Mountain): 1.36
Redding Airport: 1.33
Diddy Wells (Highway 299 East): 1.28
Shingletown: 1.12
Chico: 1.08
Red Bluff: 1.01
Hayfork: 0.46
Here are preliminary February-to-date totals, in inches, for these selected north state spots:
Brandy Creek: 12.04
Shasta Dam: 8.04
Fire Station 2 (west Redding): 7.84
Hillcrest (Hatchet Mountain): 7.04
Summit City (Shasta Lake): 6.97
Victor and Derby (Enterprise): 5.92
Upper Hilltop (north-central Redding): 5.63
Diddy Wells (Highway 299 East): 5.60
Girvan Road area (southwest Redding): 5.24
Hacienda Heights (northeast Redding): 5.18
Deschutes and Swede Creek (Palo Cedro): 4.77
Shingletown: 3.76
Chico: 3.60
Mount Shasta: 3.46
Redding Airport: 3.16
Hayfork: 2.73
Red Bluff: 2.12
Here are season-to-date totals for selected north state spots. Season starts July 1. Totals are in inches:
Brandy Creek: 49.69
Hillcrest (Hatchet Mountain): 44.33
Shasta Dam: 39.13
Summit City (Shasta Lake): 39.05
Fire Station 2 (west Redding): 34.77
Upper Hilltop (north-central Redding): 34.52
Victor and Derby (Enterprise): 32.80
Diddy Wells (Highway 299 East): 30.01
Hacienda Heights (northeast Redding): 28.97
Shingletown: 24.48
Hayfork: 24.25
Mount Shasta: 24.07
Redding Airport: 22.92
Chico: 18.69
Red Bluff: 14.71
Precip-to-date throughout the north state ranges from just a few nickels above normal at the Redding Airport to well below normal at Shasta Dam.
Feb. 24 wind report: Final
Here are top wind speeds from the Feb. 23-24 storm:
Upper Hilltop (north-central Redding): 65 mph
Redding Airport RAWS: 55 mph
Redding Airport ASOS: 54 mph
Red Bluff: 49 mph
Corning: 47 mph
Sugarloaf RAWS: 46 mph
Mule Mountain: 44 mph
Hacienda Heights (northeast Redding): 40 mph
Shasta View and Highway 44 (east Redding): 37 mph
Victor and Derby (Enterprise): 33 mph
Cottonwood: 30 mph
Palo Cedro: 29 mph
Shingletown: 26 mph
The deluge in Enterprise
A note and a couple of images from readers on yesterday afternoon's deluge as it hit Enterprise:
From the storm ... our back yard turned into a pool for a few minutes. Clap of thunder and the heavens opened. It was like we were back in Texas. For reference's sake, we're in Enterprise near Victor/Vega.
The training cell doused Parkview for a few minutes before moving on. Here are some images:
Posted by Dee Wrenched at February 25, 2008 8:31 AM
Whoeee! That was a deluge Scott. Near Hartnel and Victor our rain guage caught 0.7 of an inch in just over ten minutes.
"Training" t-storm cells forming west of town
Radar shows a line of training cells developing in the classic Igo-to-Shasta Lake alignment across the foothills west of town.
Here's a scan from 4:03 p.m. to 4:23 p.m.:
Conditions for these showers are certainly more favorable today than they were on Friday, when I talked about the possibility of their formation.
We've got strong southeast winds pushing against the foothills for orographic lift and robust cyclonic southwest flow aloft around the low off the coast creating shear that accelerates upward vertical motion. These are the triggers needed to get something going in this unstable air.
It looks like this line of showers is slowly working east-northwest, coming off the foothills into the western side of town.
We'll see what happens.
Wind report: Redding hits 55 mph
Here are top wind gust speeds reported around the far northern Sac Valley as of 12:17 p.m.:
Redding Airport RAWS: 55 mph (between 10:50 and 11:50 a.m.)*
Redding Airport ASOS: 54 mph (between 9:50 and 10:50 a.m.)
Red Bluff: 49 mph (between 7 and 8 a.m.)
Corning: 47 mph (between 9:50 and 10:50 a.m.)
Highest gust speed I've seen so far in northern California is 84 mph at the Camp Six RAWS above the Smith River along Highway 199 northeast of Crescent City.
Winds are still thumping the walls here in Parkview. More updates as warranted.
*RAWS (for Remote Automated Weather Station) reports instantaneous wind gust speeds. ASOS (for Automated Surface Observing System), used by the National Weather Service at its official stations, takes 2-minute wind speed averages.
Bluster buster
Rest of today
52 degrees
Periods of rain or showers, diminishing through the afternoon into evening
A few sun breaks possible this afternoon
Southeast wind to 30 mph with gusts to 40 mph or higher, easing during the afternoon
Partly cloudy, becoming mostly sunny
Variable wind to 6 mph
Rest of this week: High and dry
Moderate high pressure peaks Tuesday, for what could be the week's warmest day. Temps could top out in the lower-mid 70s.
The ridge starts to weaken and move east by Wednesday, which should still feel rather spring-like. The cooling trend continues Thursday and Friday as a shallow wave clips far northern California.
This wave may dip just far enough to spread clouds and a light shower threat into the far northern valley Friday afternoon into Saturday morning. Showers could be a better bet in the mountains north of Lake Shasta.
Next week: Dry and sometimes breezy
High pressure holds over the west coast all next week, shunting storms into the Pacific Northwest and keeping the north state dry and mostly mild.
We could see a coolish, breezy period around March 4 as ridging bulges far into the Gulf of Alaska, opening the way for cold air to dive down over the interior Pacific Northwest into the Great Basin. This is a classic north wind pattern for the far northern valley, though this one doesn't look like it will last more than a day.
There's no valley rain or mountain snow in sight out through March 11, from the look of the long-range forecasts today.
Discussion of today's forecast
Surface maps show the low due west of about Eureka swinging an occluded front up into southern Oregon:
The low pressure center has filled to 990 mb. That's not nearly as impressive as yesterday's 973 mb, but still a pretty deep low that's a lot closer to us today. We're still looking at a 15 mb gradient into the core only a few hundred miles west. So we can expect rather strong, gusty east to southeast winds pretty much through the afternoon, although these winds will ease up as the low keeps filling in.
In fact, winds should probably peak out by noon. They're certainly blowing hard as I type, around 10:40 a.m.
Wind will be the main story today, though we'll also continue to get valley rain and mountain snow as the low pulls moist air into interior northern California.
Indeed, the strong southeast flow into the low never did dislodge the cold air from the mountains north of Lake Shasta, and Caltrans traffic cams show snow on the ground down to Vollmers, and heavy snow falling in Mount Shasta.
Here's how the whole storm system looked on satellite as of 9:45 a.m.:
You can see the low has lost much of its distinctive pinwheel shape compared to yesterday, although it's now just off the coast.
You can also see the bright white moisture fetch the low was pulling up through California yesterday looks a little dull and disorganized today, in comparison. This is another sign the low is weakening as it loses contact with the temperature and pressure gradients that powered it.
This 11 a.m. close-up of northern California, however, shows the pinwheel pattern still very much intact:
Cloud bands radiating out from the low are still quite visible, just not nearly as extensive as they were 24 hours ago.
I analyzed the pattern on this 10:15 a.m. satellite water vapor image:
1. First looking upstream, there's counter-clockwise circulation around a low well out over the Gulf of Alaska. This low will not directly affect us. Instead, its digging and northeastward movement will help build up the high pressure ridge that will give us balmy weather this week.
2. I labeled the RIDGE instead of putting a number 2 in there, but that's what I'm talking about. There's generally clockwise motion in this ridge, which is an area where air is flowing out from a center, or diverging at the surface, causing air aloft to sink and warm to take its place. That's why, usually (though not always), ridges produce mostly clear skies.
3. What's left of the storm system today. Counter-clockwise flow around the low center to our west is still pulling moist air into interior northern California. The low will continue to pull moisture our way as it opens into a wave late this afternoon and moves off to our north.
4. The jet flowing along the ridge-trough pattern that will progress east with this low, giving us a dramatic change in the weather -- from stormy to placid -- over the next 36 hours or so.
Here's how the GFS (Global Forecast System) models the pressure patterns aloft and at the surface by 4 p.m.:
You can see there's little left of the low by this time. It's filled in to 1005 mb and it's moved to our north.
Even so, we'll still sit on the active, cyclonic side of the low, which means continued valley rain and mountain snow well into the evening.
The warm air surge I had expected with this low never did amount to much. I see temperatures changing little today from their present high-40s/low-50s on the valley floor.
Rain, wind check: Saturday/early Sunday
Here are preliminary precipitation totals from 4 a.m. Saturday through 4 a.m. today for selected north state spots courtesy of the California Department of Water Resources, the National Weather Service and the Citizen Weather Observer Program. Totals are in inches:
Brandy Creek: 2.48
Shasta Dam: 1.80
Pine Grove (Shasta Lake): 1.76
Fire Station 2 (west Redding): 1.64
Girvan Road area (southwest Redding): 1.43
Upper Hilltop (north-central Redding): 1.29
Deschutes and Swede Creek (Palo Cedro): 1.22
Hacienda Heights (northeast Redding): 1.03
Victor and Derby (Enterprise): 1.15
Hillcrest (Hatchet Mountain): 0.96
Diddy Wells (Highway 299 East): 0.96
Redding Airport: 0.96
Red Bluff: 0.79
Mount Shasta: 0.77
Chico: 0.64
Hayfork: 0.48
Shingletown: 0.44
We're not done with the rain and snow just yet, bu these totals probably represent the bulk of it. And they're not very impressive, really.
The totals do show orographic favor for southeast and south-facing slopes, as expected. Spots like Hatchet Mountain and especially Shingletown, which do better under southwest flow, have hardly gotten anything so far (though the east side of the valley will likely see more later today as the flow shifts in its favor with the passing low).
Lakehead (technically, Lakeshore), had the highest total I could find in all of northern California, with 2.68 inches in the 24-hour period.
Statewide, the highest 24-hour total I found was 3.58 inches at Anderson Peak in the Santa Lucia mountains above Big Sur. The Santa Lucias and south-central Sierra where best positioned to get enhanced precip from the jet stream, which roared into California at about that latitude below the low. Even so, given the orographics, subtropical moisture and jet interaction, even that total isn't very impressive.
As for wind, we're not quite done there, either. But so far, February's big blow has been a big bust. And that's fine with me.
Here are the top wind speeds for selected north state spots recorded as of 5:40 a.m.:
Red Bluff: 38 mph
Corning: 37 mph
Redding Airport: 36 mph
Redding RAWS: 36 mph
I checked some of the more wind-prone spots down in the Bay Area:
Pt. Reyes Lighthouse: 66 mph
Mt. Diablo: 65 mph
Hawkeye RAWS: 52 mph
Middle Peak (Mt. Tam): 51 mph
The low is still off the Redwood Coast. Water vapor loops show a much less distinct and organized structure, but surface maps still put the low center at 980 mb, which is rather deep. So we could well see stronger winds today -- more wind than rain, probably -- until the low comes ashore and starts dissipating later this afternoon.
We'll see if these winds will even match the Feb. 1-2 storm (51 mph at Redding Airport), let alone approach the Jan. 4 storm (82 mph).
I'll monitor.
Posted: 5:53 a.m.
Pretty garden variety -- so far
The fact that it's raining (and snowing in Mount Shasta, contrary to my prediction of 5,000-foot snow levels) would hardly merit mention if forecasters and wanna-be forecasters, such as yours truly, had not so hyped this storm as a big soggy bomb.
This, uh, rain event hardly qualifies as a storm, so far. It's just been a dreary garden variety northern Sac Valley pitter patter.
Precip totals haven't been impressive or even noteworthy anywhere in the state. The Clear Creek gauge above Whiskeytown is the only spot to go over 1 inch as of 3 p.m.
Other preliminary totals (in inches) as of that hour were 0.60 at Shasta Dam, 0.52 at Fire Station 2 in west Redding, 0.32 inches in Red Bluff and 0.29 inches at the Redding Airport. Thursday's rain was actually a lot more productive.
We have relatively dry air in the atmosphere to thank for the lower-than-expected -- or at least lower-than-I-expected -- snow levels (KRCR was much more on the mark). We've seen this phenomenon time and again this year, and really, it's hardly surpising in a season of long dry spells. The strong warm advection ahead of the storm has been riding up over colder, drier air trapped in canyons and near the surface. Rain falling into this drier air evaporates, cooling the air further and keeping snow levels down despite the influx of warmer air aloft. 700 mb temps aren't a very reliable index in such situations.
As for the much dreaded wind, you don't need a Weather Geek to tell you it's been a bust so far. The Redding Airport reported calm conditions just before 4 p.m. Nor could I find much wind farther south, in the Bay Area, for example, where I've always expected this storm to hit harder. Middle Peak on Mt. Tam did record a 40 mph gust shortly after 2:30 p.m., and Mt. Diablo recorded a 59 mph gust at 11:17 a.m. Other than that, not much going on down there.
The low is still spinning away out around 133 West, pulling a long fetch of subtropical moisture into interior northern California. Here's how it looked as of 4:15 p.m.:
Surface maps show the core has deepened to 973 mb, which is actually counter to expectations in couple ways -- first, the low was supposed to start filling by now, and second, it wasn't supposed to get that deep in the first place.
I still think the wind could crank up later today -- probably after dark -- as the low center approaches. And again, the strongest winds aren't supposed to hit until much later, or even tomorrow morning.
As for the rain, the developing frontal band does seem to be narrowing. But remember the low is spinning counter-clockwise, pulling moisture up from the southwest, while the jet stream flowing south of the low over that fetch is enhancing lift in the atmosphere.
So we could see that white nozzle aimed our way another 18 hours yet. We could also see the moisture band narrow farther, and just not get that much more precip as the low edges closer, pushing the main surface convergence zone east of us.
I don't claim to understand how this whole thing will play out. We could end up with just a bit of disappointment (for those who like a good storm) and relief (for those not interested in losing their electricity for a few days), or we could still get slammed.
My gut tells me this one won't live up to the hype. But my gut isn't a very good forecaster either. We'll just have to watch what happens.
Posted by Travis at February 23, 2008 5:53 PM
Wow there is snow on the Vollmers web cam....Looks like there is some cold air trapped in the Shasta Lake area...Looking at the Dunsmuir web cam there is nothing but rain. What an interesting microclimate!!! Don't think anyone saw that coming.
Rainy but calm mid-day; big blow due tonight into tomorrow morning
However much an inconvenience or even a hardship the incoming storm may ending up imposing on people, it's certainly a remarkable object, viewed from the calm distance of space.
Here's how the storm looked at 10:45 a.m.:
Here's an enhanced infrared image as of 9:15 a.m.:
And finally, the 9:15 a.m. satellite water vapor image:
Animated water vapor loops show the low has coiled up a bit more over the last few hours, wrapping cold air around itself.
Surface maps show the low occluded at 976 mb, which is probably as deep as it's going to get (for prespective, normal sea level pressure is 1013 mb, the Jan. 4 storm was 956 mb, Hurricane Katrina when it hit the Gulf Coast was 920 mb).
The surface map shows the low sitting at about about 135 degrees West and 37 degrees North around mid-morning.
This low has gone from an infant wave to a mature cyclone in just over 24 hours. This furious Speed Queen churn in the westerlies has yanked relatively cold, dry polar maritime air down from the north and shoved sultry subtropical air up from the south, producing explosive vertical motions where the air masses meet. We see this as the impressive fan of cloudiness out ahead of the low, and spreading over our skies.
A low at maturity finally wraps cold air around itself and starts to cut itself off from the sharp temperature and moisture contrast between the polar and tropical air on which it feeds. Temperature and density gradients between the two air mass types create a huge imbalance in the atmosphere that acts like a dynamo as long as it exists. All that energy is really the atmosphere trying to correct this imbalance. And cold air wrapping around the low -- the moment of occlusion -- is the beginning of the end of this imbalance.
So the storm that's coming in today will be a slowly dying storm, weakening with every hour. That's not to say it still won't kick our butts.
This graphic shows the three main precipitation bands ahead of the low, moving toward the California coast from the southwest:
Satellite precipitation estimates put hourly rainfall rates in these bands at 0.20 inches to 0.30 inches, with some rates up to 0.60 inches in the middle band. Any hourly rain rate of 0.30 inches or more ranks as heavy.
Here's how the NAM (North American Mesoscale) models the pressure gradients and precipitation fields across California and Nevada at 1 p.m. today, when we should start to see the beginning of the steady rain and increasing winds this storm promises:
Each of those black lines, or isobars (lines of equal surface pressure), represents 1 millibar of pressure difference. You can see the lines are packed rather tightly from the northern Sac Valley southwest across the Coast Range out over the Pacific into the storm core, still off this map.
Wind, which is merely the movement of air from high pressure to low, will flow at an angle across these isobars toward the storm core. That means winds in our area will start blowing from the east-southeast, and that south and east facing slopes around the valley could see enhanced precipitation due to orographic lift when these winds collide with the mountain slopes and funnel up mountain canyons.
Often with powerful storms like this the jet stream enhances precip and wind, since accelerating and/or diverging winds aloft pull air up from the surface to fill the void.
But it looks like those strong jet dynamics will occur to our south with this storm -- say, from I-80 south, or Tahoe through the Bay Area. Models also continue to show the main moisture plume feeding this storm flowing from about the Bay Area south. So, much as we saw in the Jan. 4 storm, rainfall totals may be more impressive to our south, although the north state is certainly poised for a decent soak (2-plus inches around Redding, 3-to-4 inches rain or snow melt equivalent in the mountains, more on the most orographically-favored slopes).
It looks like winds will start picking up this afternoon, but not start really blowing until after midnight, as the storm center gets closer. The highest gusts -- in the 50-to-60-mph range, or maybe up to 65 mph -- will probably blow between midnight and 1 p.m. tomorrow.
The low is moving fairly slowly, and even though it will be weakening, it will still be approaching, keeping a strong pressure gradient going for 18 hours or more. So while it's doubtful this storm will produce gusts as strong as the Jan. 4 big blow, relatively high sustained winds (40 mph-plus) and strong gusts (55 mph plus) could howl much longer this time.
Here's how the NAM models the surface at 1 p.m. tomorrow:
The image shows a much weaker (1001 mb) but still significant low just off the coast, and winds are still flowing from the southeast into this low center. You can see the model shows much higher precip rates over the slopes facing the valley than in the valley itself, but even so, rain's still falling, especially over the far northwestern valley (the Redding area), which gets enhanced rainfall in southeasterly flow.
The rain and wind should die off fairly quickly starting later tomorrow afternoon as the low finally passes over Shasta County around 4 p.m. But the southern Cascades and eastern foothills could keep getting rain and snow into the night as the flow changes to southwest on the back side of the low, and those west-facing slopes are orographically favored.
Skies will clear and calm fairly abruptly once this low passes tomorrow afternoon. Monday should be a nice day, and Tuesday could be downright balmy in the valley -- mid-70s, I'm thinking.
We may see another chance for light rain early Saturday, March 1, as a wave could dip into far northern California. Much more likely, we'll see gusty north winds in the wake of the wave that afternoon into the next day.
Storm approaching
The storm off the California coast is winding up about as expected, and it looks pretty impressive.
Here's a satellite water vapor image as of 5:15 a.m.:
The brightest areas indicate the most intense concentrations of vapor and, likely, the heaviest precip rates.
Here's an enhanced infrared satellite image as of 5:15 a.m.:
The blues and greens reflect the coldest cloud tops, which in turn suggest the most powerful upward forcing and heaviest potential precip.
Here's another image, from 5 a.m., that gives latitude and longitude grids:
The low core is probably as maximum strength right now. We'll watch it slowly become less tightly wound and organized as it gets closer.
As expected, the low is peaking out about due west of San Francisco or maybe even a little south of that, and it's tracking east-northeast.
This low has apparently tapped into subtropical moisture, which is feeding the cloud shield out ahead of the low center, just approaching the north-central and northern California coasts from the southwest. Radar shows the first light rain band off the Redwood Coast.
The satellite-derived precipitation discussion notes hourly rain rates of 0.20 to 0.50 inches where counter-clockwise flow around the low is pulling up moist air from the southwest and feeding the coldest, brightest clouds. Hourly rain rates approach 1.00 inches in a narrow band closest to the low core, where the low is pulling down dry air from the north and even, possibly, from the lower stratosphere. The boundary between the moist and dry air creates the best mechanism for forcing air upward.
Anyway, this whole mass is pushing toward the coast and, later, toward the northern Sac Valley, and should be hitting us over the next 6 to 12 hours, peaking tonight into tomorrow morning.
And I haven't even mentioned the winds yet.
I still suspect the heaviest rain and strongest winds could end up passing to our south. Part of the problem, if I can call it that, for the Redding area, as I've mentioned before, is we won't be getting winds funneling up the valley. Instead, they'll blow more from the east than the southeast, putting us in something of a rain shadow and even a wind shadow.
So after all the hype with this storm, it may not do much in the far northern valley -- which is fine, really, though we could certainly use the rain.
We'll have to see how it all plays out.
More later.
Posted: 6:00 a.m.
Posted by leroy perkins at February 23, 2008 7:39 AM
As a 40 veteran English teacher and a former journalist, I want to commend Scott Mobley for his stellar writing on everything from tough-minded investigative reporting to his entertaining and well-informed Weather Geek pieces and blogs. Scott obviously thinks for himself; his weather predictions don't just relay what the National Weather Bureau or anybody else (as far as I know) offers. It doesn't hurt that he writes like an angel. Whatever it takes to keep this luminary on the staff, I hope the _Searchlight_ will do it.
Posted by Larry Winter at February 23, 2008 9:18 AM
I concur.
Posted by Lily G. Stephen at February 23, 2008 4:15 PM
For some time, I've wanted to post a commendation about Scott Mobley's weather information. Thank you so much, Leroy Perkins, for doing it for me in your inimitable style! Although I live in Mount Shasta, Scott's forecasts provide the fine-tuned perspectives I need -- ones often including our mountain area. And as for his quality writing, we add our accolades! Our only request is that R/S feature Scott's weather forecasts more consistently on the home page. Thanks, Scott! -Lily of the mountain, www.bloomingrosepress.com
Incoming. . .
Today's turning out pretty innocuous -- nice, really. A thunder snow shower over Hatchet Mountain, and showers over the Cascades. But no training cells over the west side. Not even.
All the vort max activity I thought might kick off showers here ended up popping up from Butte County south, pretty much the way the National Weather Service predicted it would (although they called for showers up here too).
(Update 6 p.m.: A decent shower has popped up over Shasta Lake toward Jones Valley)
Of course, no one really cares about today. Everyone's wondering how bad the weather will get tomorrow.
The storm is cranking up as I type, pretty much as forecast. Here's how it looked at 4:15 p.m.:
This storm certainly looks poised for a direct hit on the north coast. But weather is dynamic, and what you see out there this afternoon isn't necessarily what we're going to get tomorrow.
There are some problems, if I can call them that, with this storm:
1. It's supposed to hit peak strength before it reaches the coast some time early tomorrow afternoon.
The NAM (North American Mesoscale) shows the low center bottoming out around 975 mb at 1 p.m. tomorrow, when the storm core is still well off the coast. That's a whopping 37 mb gradient between the surface pressure forecast in Redding at that hour and the core of the low.
(For prespective, normal sea level pressure is 1013 mb, the Jan. 4 northern California storm was 956 mb and Hurricane Katrina at landfall on the Gulf Coast was 920 mb)
But the NAM also puts the low core due west of Point Reyes at that time, which means our strongest winds would blow out of the dry east-southeast:
That wind direction isn't as conducive to good precip production as a south-southeast wind.
The low steadily weakens at it tracks northeast toward the coast over the next 12 hours. The low center fills to 991 mb by 7 a.m. Sunday, when it sits directly over Eureka:
A low right off the Redwood Coast would be better positioned to create strong winds up the northern Sacramento Valley. The pressure gradient early Sunday would still be a fairly impressive 12 mb, for rather strong south to southeast winds.
The low dies rapidly as it tracks inland over Siskiyou County through Sunday, and our wind and precip should wind down through the day.
The GFS (Global Forecast System) weakens the storm even faster. It's a wimpy 1004 mb by the time it hits the coast late Sunday morning.
2. Two of the three forecast models I've consulted take the low to our south, then track it inland over northern California in a much-weakened state.
I don't have a lot of experience trying to forecast storms this powerful that come in to our south. But, according to my limited knowledge, the most active weather stays south and east of the low center. At best, we get "wrap around" moisture and weaker vertical motions producing less vigorous lifting for rainfall on the northeast side of the storm.
(Cut off lows are a different story -- there, often, the northeast quad sees the best action).
3. The January 4 storm center went well to our north, but pushed a mammoth frontal system through northern California. Even though the core of the low was over 1,000 miles away in that storm, there was still a rather extreme pressure gradient across the front that produced some of the strongest winds ever to hit the Redding area.
It looks like any fronts generated by the incoming storm will trail off to our south, provided the low tracks as forecast. So again, we would miss the strong vertical motions that occur in frontal zones.
I've noted elsewhere that the main moisture plume feeding this storm will sag well to our south as the low approaches. But without up-valley orographic winds to wring out what moisture is available, we could wind up in a rain shadow.
Bottom line: this storm is going to hit some place in California. But we may well be spared the worst.
We'll take our break today
Rest of today
54 degrees (revised from 51 degrees)
Variable cloudiness with sun breaks
Showers possible
Variable wind to 12 mph
Increasing clouds with light to moderate rain developing by late morning or early afternoon
Rain could be heavy at times by later afternoon or evening, especially foothills and mountains
Snow level around 5,000 feet
Southeast wind to 40 mph with gusts to 60 mph developing by evening
Next week: Maybe a bit more unsettled
Strong winds could blow through Sunday as the core of the low tracks across far northern California into southern Oregon before dissipating in the evening. Strong southeasterly to southerly flow funneling up the Sac Valley will likely keep the precip going much of the day Sunday, though the rain and higher-elevation snow should taper by late afternoon or evening.
Indeed, things clear up, dry out and warm rather dramatically on Monday as a big bulge of high pressure (which is just another way of saying dry and warmer) bounces in behind the departing low. Afternoon temps would waft well into the 60s Monday and vault toward the mid-70s Tuesday, given light down slope winds.
Mid-range models are starting to suggest a much more progressive pattern next week, though. While we're not teed up for any more big storms, we could see a weak wave Wednesday that mows down the ridge, drops temps, spreads in some clouds and even a shower threat to the mountains north of Lake Shasta.
The ridge bounces back for another balmy day Thursday, followed by another weak wave Friday into early Saturday for more cooling, clouding and maybe a slight shower threat in the far northern valley.
Week of March 2 - 8: Still looks dry
Longer-range forecasts suggest ridging will hold over the west coast. Weak waves may keep riding over the top for cool-downs and cloud-ups, but otherwise, things look dry and mild to warmish as the heavy-hitting storms slug the Pacific Northwest.
Discussion of today's forecast
We're sitting between two -- or, actually, three -- waves, disturbances, whatever you want to call those things that create clouds and precip.
The low that brought yesterday's much needed steady valley rain and mountain snow is now swirling away off the Oregon coast. And the low that promises to make tomorrow night a dark and stormy one is exploding out over the Pacific as I type. But there's a third feature, just off the Mendocino County coast, that could make our weather a little more interesting this afternoon.
Here's how the whole thing looked on satellite as of 10:45 a.m.:
The Danish-shaped low off the Oregon coast is distinctly visible, as is the mass well off the coast that will be winding up into a potentially dangerous storm over the next 24 hours. Given the brightness of the clouds in that storm off-shore, I think the models are underestimating its power. However, depending on how this low tracks, the heaviest rain and even the highest winds could go to our south.
Anyway, here's a closer shot of northern California as of 11 a.m.:
We want to watch that blob of clouds off the Medocino-Sonoma County coast. Surface maps actually register a weak (1009) mb low right there. Given the cold air aloft with the general long-wave troughing overhead, and given that we're sitting under cyclonic southwest flow on the front side of this trough, it's possible this low, or vort max, could spin through later today and touch off thunderstorms or at least showers over the far northern Sac Valley. I would not rule out training cells, though I'm not exactly betting on them either. I'm being wishy washy, in other words.
I analyzed the pattern on this 10:45 a.m. satellite water vapor image:
1. Starting up-stream, we have the polar maritime air in the general long-wave trough over the eastern Pacific and now, finally, the west coast. This air is generally unstable, since it cools rapidly with height and it's coming in contact with the (relatively) warm water, which warms it from below and allows air parcels to rise. You can make out the faint speckle pattern of cumulus, which mark out rising air columns that have cooled to condensation. Such cool, unstable air also sits over the far northern Sac Valley today.
2. This is tomorrow's storm, just now starting to wind up. Look at satellite loops over the next 12 hours and watch this thing wrap into a monster. The NAM (North American Mesoscale) still models this low with a core pressure of 979 mb off the Redwood Coast by tomorrow evening. That's not nearly as deep as the Jan. 4 storm, but it's closer (although the Jan. 4 storm pushed through a very strong cold front that also had tight pressure gradients; this front, not winds into the storm core, wrecked the havoc that day).
3. A 170-knot jet at the boundary between the maritime polar air and the maritime tropical air to the south is providing the energy to feed this storm. This jet is also blowing into California to our south, providing cyclonic shear to any little vorticity maxes or disturbances developing off the coast. This shear, or difference in wind speed, helps these disturbances spin counter-clockwise. That spin, in turn, helps lift air, create clouds and precip.
4. The "X" marks a vorticity max off the coast that could swing up from the southwest through our area later today. The added cyclonic spin and energy in this disturbance could touch off training cells that align with the topography along the western foothills and the cyclonic southwest flow aloft. Or, we could get nothing. These things are notoriously hard to predict. I'm just saying conditions make these showers possible today.
5. Counter-clockwise flow around the low that brought us yesterday's rain and snow. Out of the picture, now.
Here's how the GFS (Global Forecast System) depicts the pressure patterns at the surface and aloft as of 4 p.m. today:
Main things to note are:
A) The cyanish colors over northern California depicting 500 mb heights down into the 540-to-546-decameter range. 500 mb heights are proportional to air mass warmth, and these heights are quite a bit lower than the normal 561 decameters at this time of year. The main issue for us, today, is instability and potential for showers if there's a trigger to force the air upward.
B) Bullseye of black isobars around the low developing well off the coast. That's tomorrow's storm.
Rain check: Thursday
Here are preliminary precipitation totals from 4 a.m. Thursday through 4 a.m. today for selected north state spots courtesy of the California Department of Water Resources, the National Weather Service and the Citizen Weather Observer Program. Totals are in inches:
Shasta Dam: 2.12
Brandy Creek: 1.88
Upper Hilltop (north-central Redding): 1.69
Fire Station 2 (west Redding): 1.68
Hacienda Heights (northeast Redding): 1.53
Victor and Derby (Enterprise): 1.52
Deschutes and Swede Creek (Palo Cedro): 1.51
Summit City (Shasta Lake): 1.41*
Hillcrest (Hatchet Mountain): 1.28
Diddy Wells (Highway 299 East): 1.24
Girvan Road area (southwest Redding): 1.22
Redding Airport: 0.80
Chico: 0.73
Red Bluff: 0.61
Shingletown: 0.56
Mount Shasta: 0.47
Hayfork: 0.46
Black Ranch at Vedder (Burney): 0.25
*Through 4 p.m. Thursday
A regular rainy day
Rest of today
48 degrees
Periods of light to moderate rain
Snow level around 3,500 feet
South wind to 16 mph with higher gusts
Mostly cloudy with showers likely, ending late
Snow level around 2,500 feet
South wind to 16 mph with higher gusts, easing afternoon
The weekend: Stormy!
Mid-range forecasts now pretty much agree we'll get a bit of a break early Saturday.
Then we're going to get slammed.
Forecasts show a rapidly-deepening low well off the California coast starting tomorrow afternoon. This low is supposed to deepen to 977 mb by Saturday afternoon, as it draws within a few hundred miles of the Redwood Coast. The extended GFS (Global Forecast System) puts the low center at 985 mb right off the Del Norte County coast by early Sunday morning. For perspective, normal sea level surface pressure is about 1013 mb.
Granted, this low, if it develops as forecast, would not be nearly as deep as the Jan. 4 bomber, which hit 956 mb. But this new storm would spin just off our coast, rather over 1,000 miles away off the northern tip of Vancouver Island. The NAM (North American Mesoscale) model suggests a 26 mb gradient between Redding and the low center by 10 p.m. Saturday.
A gradient that steep would create potentially damaging south to southeast winds in the far northern Sac Valley.
There are also signs this tightly-wrapped low, and its associated fronts, would draw fairly moist subtropical air toward north-central California and even into the interior. This moisture, combined with the strong surface and upper-level winds funneling up the valley, could produce impressive rainfall and higher-elevation snow fall.
Snow levels could rise to 4,500 feet or even 5,000 feet, since the low will be to our north and we would stay in the storm's warm sector. However, forecasts do suggest the low will pull down enough cold air to keep snow levels well below the mountain tops.
As we saw during the Jan. 4 storm, the juiciest moisture plume will stay to our south. But strong orographic winds could enhance precip on southeast-facing slopes in the Redding area.
Forecasts also suggest a 140-knot cyclonic jet on the front side of the trough will nose into northern California, creating speed divergence that could enhance precipitation and winds. Accelerating winds aloft in this jet would literally rip a hole in the atmosphere that must be filled from below. The divergence aloft, coupled with the inflow of warmer, moist air in the southwest flow, would encourage strong rising motions in the atmosphere that create more precip.
Finally, this low looks like it could track fairly slowly across far northwest California into southern Oregon, keeping us on the active side of the storm well into Sunday and even early Monday.
This is certainly a situation to watch to see if it develops as forecasts suggest. We could be facing our second "storm of the year" in as many months.
Next week: Warm and dry
The weekend storm would be our last for the foreseeable future, should it materialize.
Longer-range forecasts show a bulge a dome of warm, sinking, drying air building up over the west coast by Monday afternoon. Forecasts keep that big dry dome there through next week and even the following week.
500 mb heights in this warm dome could approach spring-like levels by Tuesday, when afternoon temps in the Redding area may near 80 degrees for the first time this season.
Week of March 2 - 8: Now looks dry
No sign the ridge will break down. Hello, spring!
Discussion of today's forecast
The far northern Sac Valley is finally getting some rain (the central Sac Valley actually got hosed early yesterday, but the impulse that brought those heavy showers scooted off to our southeast, leaving us with a mere pavement-dampening). Caltrans traffic cams show wet snow falling down to about Mount Shasta.
Welcome and needed though the rain may be, so far, precip rates have mostly been light -- with a few mountain spots shading toward moderate -- since things started around 6 a.m.
Preliminary precip totals as of 11 a.m. include 0.68 inches at Brandy Creek above Whiskeytown Lake and 0.31 inches at the Redding Airport.
Today's forecast challenge, of course, is figuring out how long this rain, such as it is, will last, and whether rain rates will pick up.
Surface maps show a shallow (around 1004 mb) and elongated low well off the southern Oregon coast trailing a cold front still off the Redwood Coast.
Radar shows steady light precip pumping into the northern valley out of the south-southwest.
Satellite and satellite water vapor loops show a low spinning just off the northern California coast, feeding colder air into the back of the warm frontal cloud shield and forcing it to bend a little northwest to southeast, so it almost parallels the coast line.
Here's how the whole thing looked from space as of 10:45 a.m.:
Here's a closer view of northern California. The low is the little clot-like swirl northwest of Eureka:
What happens today depends on how long that counter-clockwise swirl keeps feeding moisture into interior northern California. I tried to explain how I think things may go using this 10:45 a.m. satellite water vapor image:
1. We start upstream, with the maritime polar air flowing around a deep upper-level low in the Gulf of Alaska.
This cold, relatively moist air has been trying to get to the west coast all week. But an obstinate ridge -- the same warm dome that gave us the lovely President's Day weekend weather -- has been holding things up.
2. Nearly zonal 170-knot jet at the boundary between the maritime polar air and the maritime tropical air to the south. In general, the greater the contrast between two air masses like this, the stronger the jet stream wind and the storms that develop below.
This jet is supposed to push into California by afternoon, providing continued cyclonic shear for any counter-clockwise eddy to the north, off our coast.
3. The low off the coast. Counter-clockwise flow around this low is feeding moisture into interior northern California. We've said this is not an especially deep low. The GFS takes it down to about 999 mb by afternoon, while the NAM keeps it at about 1003 mb before it pulls into southern Oregon this evening.
Still, we should stay cloudy and rainy as long as this circulation stays off the coast, and indications are, with cold air feeding in from the west and the jet shear to the south, we should have the low going at least into evening.
4. Cloud band producing this light-to-moderate warm sector precip. The clouds are stratoform, indicating gradual lifting through a mostly stable atmosphere as warm air pulled up by the low slides over cooler air ahead of the front.
But, just because we've got a warm front going, doesn't mean our temperatures will be warm today! Cool air trapped at the surface will likely stay there, given the fairly stable atmosphere and relatively light winds. I doubt we'll ever hit 50 degrees.
Here's how the GFS shows the surface and upper-level pattern as of 4 p.m. today:
The cyanish color contours show an upper-level trough trying to develop over northern California, anchored by the weak (999 mb) surface low, forecast over southern Oregon. We remain southeast of this low, under cyclonic flow and positioned for a continued moisture feed.
The chart shows a developing gradient into the low which could generate a southeast wind later today. Winds out of the southeast orographically favor the west side of the northern Sac Valley, since they would blow perpendicular to the mountains, which would lift air and enhance precip through condensation.
However, the NAM shows a much weaker low and a weaker gradient. So while I do call for some wind this afternoon, I don't think it's going to be especially noteworthy, and I don't think we're going to see boatloads of rain anywhere, just these steady nickels and dimes.
Maybe some sunshine later
Rest of today
57 degrees
Mostly cloudy, but with some sun breaks possible
South wind to 6 mph
Light to moderate rain, easing by dusk
Snow level around 3,500 feet
South wind to 18 mph with higher gusts
Friday and the weekend: Friday, Sunday look potentially wet
Friday looks showery in the wake of tomorrow's front. We could get a bit of a break Saturday before the strongest blow in this series hits Sunday.
There's still some disagreement in the mid-range forecasts about the timing and strength of this last storm in the series.
The Extended GFS (Global Forecast System) shows a classic "bomb" (a rapidly-deepening low) off the Oregon border on Saturday. The low deepens to an impressive 972 mb by that afternoon, when it's still out around 135 degrees West -- or still about 660 miles off the coast.
The low starts filling in (weakening) as it heads in Sunday morning, and by afternoon the low is a much less menacing, though still noteworthy 996 mb as it nears the southern Oregon coast.
A low that deep and that close would kick up fairly strong winds and crank out some decent valley rain and mountain snow. But this storm would hardly rival the big blow of Jan. 4.
Other forecast models aren't even that bullish on the low. The European isn't quite as deep and takes it more north, while the Canadian keeps the low in the Gulf of Alaska while still pushing a decent cold front through northern California over the weekend.
Next week: Could be really warm, or not so warm, but it looks mostly dry
Longer-range forecasts disagree about next week.
The GFS builds a rather strong ridge over the west coast after some leftover showers early Monday. This ridge, should it verify, could give us our first 80-degree-plus afternoons this young vernal season Tuesday and Wednesday. The GFS weakens the ridge for a slow cool-down after mid-week.
The Canadian keeps the ridge axis farther west, which would put us under a cooler northwest flow, prone to weak impulses rippling through.
The Ensemble Mean -- a blend of all longer-range forecasts that could act as judge and jury here -- has been out of commission for a couple of weeks now, and won't help us. And since I'm not psychic or very skilled in decoding the tea leaves of tropical convection, I have to say I have no idea how next week will turn out.
Week of March 2 - 8: Wet pattern could return
The long end of the longest-range GFS suggests the west coast ridge could retrograde enough by early March to allow a couple of waves riding over from East Asia to drop down over the Gulf and through northern California. The usual caveat about the uncertainty of these long-range "fantasy" forecasts applies.
Discussion of today's forecast
Satellite water vapor images shows a slight low-pressure eddy just off the Mendocino County coast.
Counter-clockwise circulation around that low means winds into the interior Sac Valley are from the south. So we're getting stratus banked up against the mountain horseshoe at the far north end of the valley, and rather gloomy skies.
This 10 a.m. satellite image shows the overcast socking in the northern valley and surrounding mountains and basins:
The forecast question of the day is whether this low will hang out off the coast all day and keep sending this moist overcast our way, or if the incoming front will kick the low out of here, and short-wave ridging ahead of the front will allow some clearing and a bit of warming later on.
I'm betting the low will get kicked out and we'll see some clearing. When that happens, though, determines whether we wind up in the low-50s like yesterday, or possibly the upper-mid 50s or even a bit warmer.
Either way, today isn't going to be shirt-sleeve weather, unless you've got a pachyderm's hide.
I analyzed what I think's going to happen over the next 24 hours or so on this 9:45 a.m. satellite water vapor image:
1. A deep trough created by a powerful upper-level and surface low in the Gulf of Alaska. The GFS puts central pressure in the down to 966 mb. But that low won't affect us directly. We're interested in the frontal boundary at the eastern or leading edge of the trough.
2. 180-knot jet screaming along on the back side of the trough, digging it farther.
3. The frontal system -- overrunning warm sector clouds and precip, followed by a cold front and definite rapid clearing in the cold polar maritime air behind the front. We can't see it yet, but a wave is supposed to develop along this front as it approaches tomorrow, giving the whole system a bit more punch.
4. The counter-clockwise flow around the low that moved in behind yesterday's weak front. Even though we did not get enough rain yesterday to bead a newspaper wrapper, a little vorticity max or burst of energy rounded the low like a spoke yesterday evening and exploded over the south Bay Area, dumping on southern Alameda County and causing some flooding. The line of showers eventually slogged into the Sac Valley, dumping on metro Sacramento as far north as Oroville.
5. I think this low will weaken and head southeast today as the front pushes in. Later today, we could get a drier northwest flow on the back side of the low that could partially dissolve some of these clouds.
Change in the weather
Rest of today
53 degrees
Mostly cloudy
Showers possible from early afternoon into evening
Snow level near 6,000 feet, lowering to about 3,500 feet tonight
South wind to 6 mph
Becoming partly cloudy
Wind shifting northwest to 12 mph with higher gusts
Rest of this week: Could be rather wet in the valley, white in the mountains
Mid-range models show a stronger wave approaching later Thursday that could hang around well into Friday, finally giving the north state a decent soak.
Forecasts also indicate, once again, a deep low could explode off the Oregon border and move ashore later Saturday, whipping up strong winds. This is the "bomb" the longer-range forecasts have been hinting at for days now.
Next week: Looks mostly mild and dry after a stormy start
The extended GFS deepens to low to 978 mb off the Oregon border, then weakens the low to 984 mb as it approaches the coast Sunday morning. The Jan. 4 low bottomed out at 957 mb, but was much farther away.
Even a 984 mb low is still exceptionally deep. Pressure gradients would be tight and southeast winds would be strong and potentially damaging with a that deep passing so close. This far out, I'm not convinced the storm is going to develop as forecast, but it's certainly worth watching and noting the Canadian is coming on board with a strong low too, though not as deep and farther north.
Wind, rather than rain and snow, would be the main weather stories should this low develop as forecast. But we would also get a decent shot of precip Sunday into Monday.
Longer-range forecasts now show ridging across the west coast much of the week in the wake of this low.
Indications are a wet pattern could return in early March.
Discussion of today's forecast
Surface maps show a cold front hanging off the California coast. And satellite images show this front stretched like taffy between the parent low way up near Kodiak Island atop the Gulf of Alaska all the way down to Santa Barbara.
The big dome of warm air that gave us our nice weekend is still indirectly controlling our weather by eating this front for breakfast, lunch and dinner.
Here's how the front looked as of 9:15 a.m.:
Here's a closer look at the cloud band over far northern California, as of 10:30 a.m.:
I analyzed what's going on with this front, and had a look at the weather up-stream, using this 9:15 a.m. satellite water vapor image:
1. As always, we start up-stream, since our weather generally moves from left to right, west to east. Here we see the polar jet just before it bends sharply north around the downstream ridge, which is still a huge obstruction. We're not going to get any real weather until all that jet energy out there works east, toward us, around Thursday or Friday.
2. A low that's developed behind the front. This low could reinforce the front later today, leading to better shower chances later this afternoon into tonight, should things hold together.
However, it looks like this low is getting squashed up against the ridge too, so it may not do much for our rain needs.
3. The stretched-out cold front. I won't rule out showers, but this thing just doesn't look very impressive, and it may just get hung up off the coast and dissipate. The farther east you are, the lower the precip chances.
4. The ridge that's causing all the blockage and wreckage of our weather, creating this sterile gloom (though for those who don't especially like warm sunshine, today's got to be a welcome change).
A look out the window confirms the overcast ceiling is still rather high as we approach late morning. Radar has shown light-to-moderate rain over northern Humboldt County and, surprisingly, a second bulls eye of activity along the central California coast. A few light echoes have strayed into Trinity County.
We'll see if the atmosphere moistens enough to support rain over the far northern valley.
Here's how the GFS shows the upper-level and surface pressure patterns as of 4 p.m. today:
The green hump just to our east indicates the ridge, which is surprisingly strong considering its relatively low 500 mb heights. The ridge axis has been driven all the way back toward the Great Basin and the interior Pacific Northwest -- a couple hundred miles farther east than this morning. It's pretty slow progress.
The map shows that most of the baroclinic zones, or areas where the surface isobars are tightly packed, sit hundreds of miles off to our northwest, closer to the maritime polar air. So we won't be seeing any strong winds this afternoon, or much of any wind at all.
The overcast and colder air filtering in with the approaching trough should hold temperatures to the lower-mid 50s -- especially if we do get some rainfall later today, and the air cools through the swamp cooler effect.
But it's also possible these clouds may not thicken enough to keep temps from wafting into the upper-mid 50s or even higher, as most forecasters are predicting.
That's still a lot cooler than yesterday or Sunday.
One last nice day
Rest of today
68 degrees
Sunshine sometimes filtered through high clouds
North wind to 6 mph shifting south and becoming nearly calm
Mostly cloudy
Light showers possible
South wind to 5 mph
Rest of this week: Coolish and wettish, with decent soak possibly postponed till weekend
Mid-range forecasts have turned a bit bearish on the wave that showed so much promise for later this week, around Thursday/Friday.
The extended GFS (Global Forecast System) now suggests troughing in the west may need a little more time to really get organized.
Thursday and Friday still look like potentially wet days. But the stronger weather system now holds off till Saturday, in the GFS at least. Low snow levels no longer look like such a threat.
The Canadian holds the Thursday front together a bit better and brings in another decent wave Saturday.
We'll see.
Next week: Mixed bag
Longer-range forecasts now suggest a strong ridge will build over the west coast early next week in the wake of the weekend trough.
But this ridge, like the trough, looks transient. It could move on through after delivering a couple spring-like days Monday and Tuesday, replaced by a zonal flow that could bring more valley rain and mountain snow (with middling snow levels) later in the week and on into early March.
Wondering what happened to the big bomb the GFS forecast for northern California on Feb. 26? That model still develops the low, but the California ridge shunts the storm well to our north.
Bottom line: I don't really have any idea what might happen toward the end of the month and into early March, based on these cloudy crystal balls.
Discussion of today's forecast
Skies are clear over interior northern California except for some high clouds. Here's the view from space as of 10:30 a.m.:
A stratus deck hugs the coast and even socks in much of the Bay Area. That stratus deck was out there yesterday and did little to keep northern valley temps from wafting to an unseasonable 70 degrees. High clouds and a bit of cooling up-valley flow may keep today's temperatures a couple degrees lower -- you may not notice much difference.
A broader satellite view shows other changes to come. This shot is as of 10:15 a.m.:
The cold front at the leading edge of a developing trough off the west coast looks fairly impressive. But forecasts suggest this front will act mainly as a sod buster, spending most of its energy shoving the ridge east and moistening the atmosphere after a two-week rainfall hiatus.
I analyzed the evolving pattern on this 10:15 a.m. satellite water vapor image:
1. Robust East Asian jet (up to 200 knots) and polar air just to the north carving a trough and helping develop a 996 mb low in the Gulf of Alaska. This low is forecast to deepen to 980 mb by afternoon, but harmlessly ride up the back side of the ridge over the west coast.
2. Fat-looking cold front at the leading edge of the developing trough, which is a giant bag of cold air spreading south.
This is the front that's supposed to waste itself pushing against the mass of drying, sinking air under the ridge over whose axis is just east of us right now. Forecasts indicate the front will have only a few light showers left for us, just enough to slicken the streets. We'll see whether it holds together better than expected.
3. The weird little cut-off low that's been pinwheeling away under the ridge, first pumping it up and now helping to weaken it, since counter-clockwise air flow tends to converge at the surface, rise, cool and condense. That lifting helps moisten and cool the atmosphere, weakening the ridge.
4. Bands of high and middle clouds associated with the cut-off low. The fact is, there's not a lot of moisture to work with, so this low, unlike others we've seen this winter, won't deliver much weather.
The GFS shows a steadily weakening, yet persistent ridge over the west coast by 4 p.m.:
The yellow-green hump in the color contours over the west coast is what's left of the ridge. 500 mb heights -- which are a fairly direct index of airmass warmth -- will have declined from about 580 decameters on Friday to about 568 decameters by this afternoon, if this forecast is right.
However, forecast 850 mb temperatures don't really drop off much today from yesterday, staying at about 8 or 9 degrees C. Air that warm mixed to the surface would support a top temp in the upper-60s.
I had originally forecast mid-60s today, but I'm tweak for upper-60s now. T-shirt weather either way.
Bad forecasts, great weekend
Yesterday, I was pretty confident we'd get to 70 degrees -- or close to it, with a massive mound of warm air marching in off the coast.
But temperatures stayed just a bit on the cool side of mild, never getting above 65 degrees.
The big mountain of warm air didn't look like it would be any warmer today. We'd have thin high clouds and a potentially cooling up-valley wind again.
So I assumed we'd stay in the mid-60s once more. Instead, afternoon temps wafted right toward the 70-degree mark I'd expected yesterday.
The atmosphere, sometimes, is a mystery -- at least to me. But I could not let a pair of bad forecasts ruin a gorgeous weekend.
Fair weather friend
Rest of today
66 degrees
Fair with occasional high clouds
North wind to 8 mph becoming light and shifting south
Mostly fair morning; increasing high clouds afternoon, especially south
Light and variable winds
Rest of this week: Cooling off; Thursday/Friday still looks wet or white
Mid-range forecasts still have a bead on a consolidating polar jet bringing a big change to the weather pattern by mid-week.
Tuesday looks like the transition day. We could see increasing clouds and an outside chance of light showers, mainly mountains, as the first weak ripple in the westerlies essentially sacrifices itself shoving the ridge east.
Wednesday looks mainly dry at this point. But a stronger, deeper wave looks like it could approach Thursday, bringing the far northern valley its first solid soak -- and the mountains their first decent snow -- in about two weeks.
There's some indication in the GFS (Global Forecast System) the jet orientation could take the core of Thursday's storm just to our south.
Snow levels could drop well into the foothills Friday behind the front, but precip doesn't look heavy that day.
Another, somewhat weaker but rather cold short wave trough could take a more northerly track and paste the north state with low snow on Saturday.
Next week: Big storm on Feb. 26?
The extended GFS once again shows a bomb off the Oregon Coast -- this time, the Tuesday after next.
The Canadian, once again, shows no such thing -- in fact, it shows ridging that day.
Right now (and this way too far out for precision), the GFS puts the core of a rapidly-developing low at 975 mb off the north-central Oregon coast Tuesday afternoon. The low would not be as deep as the Jan. 4 storm (that one was down to 956 mb), but it would be somewhat closer to us.
This is all speculative, of course, looking 10 days out. But for those who care about such things, it's worth noting Ed Berry, generally regarded as the guru of long-range forecasting based on global interactions between the tropics and the mid-latitude jets, has for weeks now been predicting storm comparable to Jan. 4 to hit somewhere on the west coast some time in late February or early March.
Read the whole thing if you want to go way deep into this stuff.
Discussion of today's forecast
Early morning temperatures touched freezing in parts of town under clear, calm skies, dry air and the long-winter night.
But despite the mountain snow and chilly valley temps, the satellite reflects a summer -like stratus deck along the coast with fair skies and a few high clouds inland. Here's a satellite shot as of 9:15 a.m.:
The high amplitude ridge we saw off the coast yesterday -- and which did not warm temperatures as much as I had expected -- is closer to shore today. The ridge axis hasn't quite made it ashore yet, though, which means we're still sitting under a relatively cool northwest flow aloft.
But this ridge also hosts a low pressure circulation near its base that will start to affect our weather over the next 36 hours or so. This low is already starting to pump a southwest flow into northern California. The marine flow could bright light up-valley winds that keep us from warming up as much as we would otherwise.
I analyzed the flow pattern on this 9:15 a.m. satellite water vapor image:
1. Counter-clockwise flow around the low that is pushing up the ridge and forcing it inland. This low will hearld a pattern change by later Tuesday as it approaches the coast.
2. 130-knot polar jet arching clockwise around the high-amplitude ridge. Winds flowing clockwise generally converge in the upper-atmosphere and eventually sink, since the stable stratosphere keeps the air from rising any more and the air must go somewhere. Air warms adiabatically, or through compression, as it sinks, evaporating its moisture and generally suppressing clouds in the ridge -- except for stratus, which forms when air close to the cold ocean surface cools and condenses, then lifts until it hits the lower inversion created by the sinking air above.
3. Cool northwest flow aloft over northern California down the front side of the ridge off the coast.
4. Counter-clockwise flow around the weak low in the ridge starting to bring southwest flow toward interior northern California. Southwest flow is tricky -- it can mean rain in winter, a warm wave in spring but, when there is stratus off the coast, a coolish, moist marine invasion.
5. The weak upper-level low. This low is supposed to slowly deepen and help erode the ridge. It could spread high clouds into our skies by tomorrow afternoon, but not much more weather than that.
This GFS depiction of the upper-level and surface pressure patterns by 4 p.m. today shows the ridge axis roughly along the coast, but the ridge itself starting to weaken:
The yellow-orange contour we saw in the ridge yesterday and modeled this morning is gone by afternoon, signaling slightly lower 500 mb pressure heights and a slight cooling of the airmass, since 500 mb heights are proportional to temperature.
But this is a minor height drop, and forecast 850 mb temperatures don't change, really, from yesterday afternoon.
We did not get the full warming from the mix-down and warming of 850 mb forecast temps yesterday. Conditions look similar today, with dew points climbing as marine air seeps in given the southwest flow, so I kept top temps close to the mid-60s rather that the upper-60s or even low 70s we could expect if the wind were blowing from the north.
Widely-spaced isobars on the chart suggest light winds, at best.
Sunny side up
Rest of today
69 degrees
Fair with light haze
Light winds
Mostly sunny
North wind to 10 mph developing
Next week: Cooler, cloudier and possibly stormy around Thursday/Friday
Mid-range forecasts still suggest the polar jet will consolidate, turn more zonal and blast away the ridge that's bringing us the current spring-like weather starting late Tuesday.
It looks like the heavier weather will hold off until Thursday/Friday. Everything else is either light sod-busting stuff or post-frontal showers.
The Thursday/Friday wave will mix subtropical and Arctic air, much like the late January storms. At this point, it looks like Thursday will deliver the heavier blow, with snow levels around 3,500 feet.
But Friday brings the real danger for low snow, as true Arctic air arrives with a second impulse generating more precip. We could see snow levels down to 1,000 feet or even lower on Friday.
Of course, it's way too soon to get a reliable read on details like snow levels, which are notoriously difficult to predict even when the storm's right on top of us.
Next weekend looks cold and unsettled -- pretty much a mirror opposite of this weekend.
Week of Feb. 24 - March 1: Continued unsettled
Longer-range models suggest a pattern-change the week after next that could deliver storms with a more southwest, subtropical trajectory into the west coast.
This is a development to monitor. Everyone knows the potential flooding problems if warm, Hawaiian rains fall copiously on recently-deposited cold, Alaskan snow.
Right now, however, indications are the storm track will go mainly into the Pacific Northwest.
Discussion of today's forecast
Strong winter-time high pressure has brought clear skies to the west coast from Cabo all the way up through Portland. This satellite image shows the west as of 10:15 a.m.:
I analyzed the flows creating these clear skies on this 10:15 a.m. satellite water vapor image:
1. Counter-clockwise flow around this weak low is, ironically, also helping pump up the west coast ridge -- at least for now. But that will change over the next 48 hours as counter-clockwise flow in the low creates rising motion which cools the air, eventually Swiss cheesing a hole in the ridge and weakening it. Meanwhile, this low is supposed to drift toward California as it deepens, bringing cooler temps by Monday afternoon.
2. Northwesterly flow down the front side of the approaching ridge. This flow will move east today as the ridge axis pushes toward the coast.
Clockwise circulation in the ridge generally leads to air flowing out from the center of high pressure and sinking toward the ground. Sinking air warms by subsidence, evaporates moisture and inhibits clouds formation (except for coastal stratus, which is created when air contacts chilly ocean waters and condenses, forming fog).
3. The low over the desert Southwest that brought us our north winds this week, delivered a freak snow storm to San Diego County late Thursday into Friday and now promises to stir up trouble in the southern Plains and on east.
The (finally) dead north winds -- and the dry air they brought -- allowed the ground to rapidly radiate heat and early morning temps to drop into the lower-mid-30s around town and even dip a couple degrees below freezing in lower-lying, sheltered places around Palo Cedro.
Temperatures will have a much bigger hole to climb out of today to make it toward 70 degrees than they did yesterday, when the north wind kept early morning lows close to 50 degrees and provided adiabatic warming well into the afternoon.
I think we have a reasonably good chance of making it well into the upper-60s today, though I'm not quite so bullish about the mid-70s KRCR is forecasting, given the lack of warming down slope winds today.
Here's how the GFS (Global Forecast System) depicts the surface and upper-air pattern by 4 p.m.:
The color contours show 500 mb heights -- literally, the elevation of the 500 mb height surface above sea level. Since warm air is more expansive than colder air, these heights are directly proportional to airmass warmth.
The chart plainly shows the high-amplitude ridge, or huge mound of warm air, piling up along the west coast. The yellow-orange contour running northwest-to-southeast through the north state represents 500 mb heights in the 576-to-582 decameter range, which is well above the 560-decamter average for mid-February.
Forecast 850 mb temperatures, however, are supposed to hit about 8 degrees C. Air that warm mixed to the surface would yield a top temp of about 69 degrees.
The lack of tightly-packed isobars (the black lines representing equal surface pressure) suggests light winds this afternoon across far northern California. I see the light winds and overnight temperature inversion have allowed some haze concentrations to develop in the far northern valley. I kept the haze in today's forecast and should have thought to mention it yesterday.
Warmer and calmer today
Rest of today
69 degrees
North wind to 15 mph, easing to 8 mph this afternoon
Mostly clear
Variable wind to 8 mph
Next week: Could see cold, wet pattern return
Mid-range forecasts suggest the weekend warm wave won't last. The north state could see cooler, cloudier weather by Monday afternoon, and more likely by Tuesday morning, as a super-charged polar jet blowing off east Asia stretches across the Pacific toward northern California, shoving the warm air ahead of it and ultimately out of our area.
These forecasts don't yet agree on how severe this next possible round of cold storms will be.
The extended GFS (Global Forecast System) is most bullish. That model suggests a solid sod-busting soak on Wednesday afternoon, followed by another potential low-level snow-maker on Thursday afternoon.
And then -- get a load of this -- a 951 mb low off with a subtropical tap explodes off the Oregon border by Saturday afternoon. This would be a classic west coast bomb, something you're lucky to see once a decade, let alone twice in one season.
A storm that deep with that kind of moisture would be even worse than the Jan. 4 big blow, worse perhaps than the devastating Dec. 1995 storm.
Do I think it will happen? I have to fall back on my usual excuse -- too soon to tell. But I will repeat sheer statistical probability says it's not likely.
The Canadian model does show a deep low with a subtropical tap, but keeps it well off the coast. The Ensemble Mean continues with weak precipitation probability signals for northern California through the week.
Week of Feb. 24 - March 1: Looks unsettled
The long-range GFS suggests a series of cold storms -- much like we saw in late January into this month -- continuing through the week after next.
The Ensemble Mean keeps weak precip probability signals over northern California.
Forecasters who monitor the turbulent tropics, the ultimate source of all the energy that creates our weather, have said for a long time the west coast is due for another outbreak of cold storms.
We knew this mild, rainless interlude would not last, not this winter. It's just a matter of time.
Discussion of today's forecast
Skies are clear up and down California and even much of Oregon under cool northwest flow on the front side of a large west coast ridge:
This image doesn't show the gusty north winds that have been buffeting northern California and also baffling forecasters, or better, making them look stupid (I speak for myself as a pseudo-forecaster).
The winds, expected to ease up yesterday afternoon, kept blowing through the night, keeping overnight lows from falling much below 50 degrees, well above widely forecast early-morning lows in the mid-to-upper 30s (a sure thing if the wind had died).
And the winds are still blowing as we approach mid-morning. The Redding Airport has recorded gusts up to 22 mph between 9 and 10 a.m. And if anything, the pressure gradient creating these winds seems to have tightened over the last 12 hours or so.
I used this 9:15 a.m. satellite water vapor image to analyze what's going on with these winds, and why I think they should finally ease before dusk. As usual, we look upstream first, and the riddle of the wind doesn't come until last:
1. Weak low over the Gulf of Alaska rolling over the top of the west coast ridge that will soon dominate our weather. This low is supposed to move inland today, and then absorb into the polar westerlies as the west coast ridge amplifies.
2. Weak jet (about 100 knots, that's weak for winter) at the base of the trough, over the ridge (below).
3. The jet blows into the western Canadian plains, then doubles back in a backward-S toward the California coast around the deep upper-level low that created our cool down the other day and has been responsible for our winds. This northerly flow aloft has kept the winds going -- though there are signs it is finally moving east, out of our hair, with the low itself.
4. Counter-clockwise flow around the low. Other than the obnoxious wind, this low affected us only indirectly, since it detoured around us over the top of the ridge.
5. This low is going to become a brute over the weekend as it finally heads east -- first delivering snow to the Southwest, then severe weather to the southern Plains as it moves into Texas and starts sucking up some Gulf of Mexico moisture. By Monday afternoon, it will batter the east coast with heavy snow and rain.
But, for us, the low ejecting east means the pressure gradient across California and the winds finally die down. And we get spring fever as a rather highly amplified ridge moves in, continuing the mostly clear skies and bringing warmer temperatures.
Here's how the GFS depicts the pressure pattern aloft and at the surface by 4 p.m. today:
First, looking at the color contours representing heights of the 500 mb surface, the warm colors in the expanding ridge already poke into northern California. These 500 mb heights are proportional to air mass temperatures, since warmer air is more expansive than colder.
The yellow color contour over far northern California represents 500 mb heights in the 570-to-576-decameter range, which is well above average for this time of year.
The upper-level low over the Southwest is also clearly visible in the cooler greenish colors. We see the low center is supposed to have shoved on almost into far southwestern New Mexico by this afternoon, well away from us.
The black lines, or isobars, represent equal surface pressure and are key to predicting wind speed and direction.
These maps over the past couple days have showed a ladder-like pattern of isobars across California, representing a steep gradient between higher pressure to the north and lower pressure to the southeast, around the low. It's the classic signature of a strong north wind.
That ladder of isobars is supposed to be gone by afternoon, which indicates much lighter winds. Of course, everything depends on whether the low over the Southwest keeps moving, as animated water vapor loops indicate it's moved so far today.
With the low leaving and the ridge moving in behind, forecast 850 mb temps are supposed to jump up to 9 degrees C by afternoon, compared to about 2 degrees C yesterday and Wednesday.
Redding Airport temps are already much warmer than they've been. The airport reported 60 degrees just before 10 a.m. -- just a degree shy of yesterday's high and already a degree above Wednesday's.
Noting that trend, I goosed my forecast high up from 66 degrees to 69 degrees. Mix-down and adiabatic warming of today's forecast 850 mb temp would support an afternoon high of 71 degrees, and I would not be surprised to see us hit that.
What happened to our warmer, calmer day?
Today never calmed down or warmed up quite as much as I predicted -- or, let's be honest, quite as much as I had hoped it would.
Wind gusts at the Redding Airport hit 37 mph this morning and were still huffing and puffing at over 31 mph as late as 4 p.m. Winds today were actually stronger than they were yesterday, which I had thought would be the windy one.
Afternoon temps peaked at a rather tepid 61 degrees -- just a couple degrees above yesterday and, actually, about normal for this time of year. I had supposed mid-60s when I made my quick forecast this morning.
Now it seems I jumped the gun a little when I talked about the beginning of a warm-up today.
But I still think shirt-sleeve weather will return to the valley floor tomorrow -- and certainly Saturday.
Bright and breezy today, warmer tomorrow
Winds should ease today and top temps should pop up toward the mid-60s as the mound of warm air massing off the coast marches inland.
Tomorrow should bring even warmer temps and calmer skies. Enough to generate spring fever.
I've got no time for a full forecast with a discussion today. We'll try for the whole shebang tomorrow, including a check up on a possible pattern change for next week -- perhaps a shot of rain and snow Wednesday, followed by another Friday.
I will say that as of today, next week's rains look like no reason to haul out the boats. But our official season-to-date rainfall total at the Redding Airport slipped back below normal yesterday, and at this time of year, the deficit widens pretty fast. So we'll take what we can get.
All abluster
Rest of today
59 degrees
Mostly sunny with occasional high clouds
North wind to 25 mph with gusts approaching 40 mph
Mostly sunny with occasional high clouds
North wind to 20 mph with higher gusts, easing and then picking up overnight from the northeast
Friday and the weekend: Warm and dry
The gusty north winds should blow themselves out by Friday. Afternoon temperatures will likely waft well into the 70s as the strongest high pressure yet this season mounds up along the west coast from Baja to Vancouver.
Next week: Cooling off, then maybe a shot at some rain and snow
At least one mid-range model suggests energized polar westerlies will flatten this strong ridge and shove it east for cooler, cloudier days starting Monday and certainly by Tuesday.
This more moist, cool and zonal flow could open the way for a couple of Pacific fronts by Wednesday and Thursday. The weather clears and warms in time for the weekend.
The operational GFS (Global Forecast System) is the most bullish on this idea. The Canadian holds off any precip until Friday and doesn't show much.
The Ensemble Mean also continues rather weak with its precipitation probability signals over the west coast next week, suggesting the best chances (such as they are) around Wednesday.
Week of Feb. 24 - March 1: Starts warm, then big chill down
The long-range operational GFS suggests another polar trough developing over much of the continental US the last week of February.
This would be a rather cold, and not necessarily very wet pattern, should it develop. It's too soon to say for sure.
Discussion of today's forecast
Today's big story is the wind. Gusts out of the north-northwest have already approached 30 mph at the Redding Airport this morning, and speeds will get higher as the day goes on and the wind shifts north-northeast.
These winds could also whack a good 10 degrees off today's top temp compared to yesterday. And the breeze will make the air feel even colder.
Surface charts show a 1006-mb low over western Nevada trailing a weak cold front through north-central California and a 1036-mb high well off the Pacific Northwest coast. The wind is a the rush of air from this high pressure off the coast area into the low over the Great Basin.
This 9 a.m. graphic shows the gradient mainly off to our northwest this morning:
This gradient will shift east as the colder air behind the trough works into the Great Basin. So we're going to be stuck with these winds for at least the next day-and-a-half.
I analyzed the flow patterns creating today's weather on this 9:15 a.m. satellite water vapor image:
1. High pressure bulging into the Pacific Northwest. This ridge will control our weather later this week, into the weekend, probably bringing us our warmest afternoon temperatures yet this season.
2. 150-knot jet stream blowing almost directly out of the north down the back side of the trough over the Great Basin. This jet will be reinforcing the north winds and helping direct colder air into the north state.
3. Counter-clockwise circulation around the low now over western Nevada. This low is dropping abruptly south, and will soon draw cold air into the Great Basin that will further tighten the pressure gradient across northern California.
Here's how the GFS depicts the surface and upper-air pressure patterns as of 4 p.m.:
We're most interested in the isobars, or the black lines showing equal surface pressure. You can see these lines run east-west and are packed fairly tightly in a ladder-like formation across California.
That's the signature of a strong north wind.
Also notice how the color contours, which represent 500 mb heights, run almost north-south and quickly drop from the warm colors (high heights, warm airmass) off the coast to the cooler colors (low heights, colder airmass) inland.
The jet runs at the boundary between those warmer and colder colors, where the density contrast between the airmasses is greatest. The jet has moved farther to our east afternoon, with the trough.
We can see the coldest air is well to our east by afternoon, too. Still, forecast 850 mb temperatures show serious cold air advection with this trough through the day.
So top temp forecasts are tricky, and the models are all over the place. Some model soundings say we'll get only to 53 degrees today -- which means we won't get any warmer than we are now -- and others take us all the way into the mid-60s.
We know north winds blow down slope, compressing and warming adiabatically. But on days like today, with strong cold air advection, the mix-down of colder air will offset a lot of the adiabatic warming.
I decided to go with a sort of middle-of-the-road forecast, and put our max temp just under 60 degrees. But that's a wishy-washy, hedging kind of forecast which means I really don't know.
One more day of classic false spring
Rest of today
71 degrees
Mostly clear with some thin high clouds
North wind to 5 mph
Changeable skies with variable clouds
North wind to 25 mph with higher gusts, especially afternoon and evening
Rest of this week: Warm and dry
Gusty north winds will likely blow well into Thursday, and perhaps even Friday. But temps will rebound, leading to a balmy weekend with afternoon highs back into the mid-70s.
Next week and a bit beyond: Mostly mild, but change possible late in the week
The longer-range models keep ridging over the west coast through most of next week for continued dry, mild, basically inoffensive and uneventful weather. I don't even see much wind.
The extended GFS (Global Forecast System) does want to change the pattern by Thursday, Feb. 21, when it shows the polar jet marshaling its forces and digging south with a serious trough that could deliver the north state a solid soak.
But the Canadian doesn't show this front digging far enough south to get us, and the Ensemble Mean is weak with the precip probability signal.
The pattern change will come. But the wait could be long. Might as well enjoy the mild weather while it lasts.
Discussion of today's forecast
A cloudless morning over interior far northern California. Here's how the north state looked from space as of 9:30 a.m.:
The blob of surface high pressure that sat to our north yesterday morning and gave us our gusty winds has moved east with the cold air. Gradients from southern Oregon into northern California are weak this morning, so we're not going to get blown around so much today.
This 9:15 a.m. satellite water vapor image gives us a good look at the flows creating this benign proto-spring weather, and the changes to come that will gin up the winds again tomorrow:
1. 120-knot jet blowing between a large upper-level ridge over the northeastern Pacific and a trough, or big pouch of modified Arctic air, rippling toward western British Columbia.
The behavior of this jet as it creates the snaking, shifting boundary between this warm and cold air is going to play a big role in our weather over the next 48 hours.
2. Counter-clockwise circulation around the low at the core of this trough. The low is moving east and weakening. But it's expected to push into British Columbia and then plunge south into the interior Pacific Northwest and the Great Basin, sluicing cold air to our east.
Meanwhile, the ridge over the northeastern Pacific is supposed to bulge east, too. So the ridge-trough pattern across the west is going to get much more meridional, or highly amplified. In fact, the jet will be running north-south over the Great Basin by tomorrow afternoon. And sharp contrasts between warmer air over the west coast and colder air over the Great Basin and Pacific Northwest will severely steepen pressure gradients, which is a fancy way of saying it's going to get windy.
3. But for today, we're sitting under clockwise flow that's bringing warm air up from the south. Clockwise, or anticyclonic flow, also tends to create air that sinks (just as, in general, for reasons I don't know, whenever you want to tighten a screw or a lid, you turn it clockwise). And air that sinks also compresses and warms. Provided there's no moisture added to this warming, sinking air, it will dry out. This is what happens, usually, in what forecasters call a high pressure ridge like the one sitting over northern California today.
The low moving toward the BC coast is steamrolling this ridge and pushing it east. Here's how the GFS depicts the pattern for 4 p.m. today:
The color contours represent the elevation of the 500 mb surface, which averages about 19,000 feet above sea level but varies substantially depending on whether the airmass below is warmer or colder.
The warm colors representing unseasonably high 500 mb heights still bathe California. But there's already a dimple visible in the ridge as the approaching trough, with its polar air, bites in.
500 mb heights over far northern California drop from yesterday's 580 decameters into the yellow band, which represents heights in the 570-to-576-decameter range. Remember, high heights indicate warmer air, and low heights, colder air.
Those heights forecast overhead today are still well above average for this time of year, even if they're not as high as yesterday.
Meanwhile, forecast temperatures at the 850 mb level, or roughly 4,500 feet directly overhead, are only a degree or so C lower than yesterday.
The widely-spaced isobars (the black lines on the chart representing contours of surface pressure) indicate only light north winds today. North winds yesterday added some warming, since they blew down slope and heated through atmospheric compression.
We could still get some warming from today's light north winds. In fact, sometimes, though not always, the lighter the wind, the better the warming effect. We do have to take into account these winds could be mixing down somewhat cooler air by afternoon.
We're also starting today with lower early morning temps than yesterday -- down to about 40 degrees.
So in my forecast I made today's top temp a few degrees cooler than yesterday, but still about 11 degrees above normal for the date.
It's worth noting, however, that temps today so far are running 8 degrees below yesterday, thanks mainly to the lack of warming down slope winds and the cooler start.
It's not spring -- but it sure feels that way
Rest of today
75 degrees
Mostly clear with some thin high clouds
North winds to 15 mph with higher gusts, easing after dark
Mostly clear with some high clouds
North wind to 5 mph, shifting northwest after dark and increasing to 18 mph
Rest of this week: Windy Wednesday into Thursday, then more early spring
Mid-range forecasts remain unanimous that a wave will ride over the top of the west coast ridge and plunge into the Great Basin late Tuesday into Wednesday in classic "insider slider" style.
These cold sliders almost always mean gusty north to northeast winds in the far northern Sac Valley and across much of northern California. The wave -- which is nothing but a burst of turbulent, cold air -- creates a sharp temperature contrast with the mellow, spring-like air bathing us, with the pressure much higher in the denser, colder air.
So, just as you when you release any contents under pressure, this cold, dense air will want to rush toward us, where the air is warmer and the pressure is lower. That's really all wind is, in the simplest terms.
The pressure difference should relax by Thursday afternoon, when the coldest air is well to our east and warmer air replaces it.
Ridging looks likely to bulge once again along the west coast, in other words. Forecasters -- confusingly in light of the discussion above -- call such ridges "high pressure." Warm air is more buoyant and energetic than cold, so it exerts greater pressure throughout the atmosphere. But cold air, being more dense, creates higher pressure at the surface than warmer air, and that contrast creates the gusty north winds that I, personally, don't especially enjoy.
Anyway, the ridging -- and all that warm weather -- looks like it will stay with us from Thursday afternoon through the weekend and well into next week. We're talking afternoons well into the 70s.
Next week and a bit beyond: Maybe a wet pattern returning, maybe not
The on-again, off-again idea of a wet pattern returning after mid-February is on again -- at least in the long-range GFS (Global Forecast System). This model shows the strong east Asian jet pushing across the Pacific toward the west coast. Though the jet weakens before reaching us, it sends a series of waves through northern California starting about Wednesday, Feb. 20.
It's worth noting the more conservative Ensemble Mean -- a blend of all long-range forecasts -- is much weaker with this idea. The Mean does not show a very strong precip probability signal for northern California from Feb. 20 on, at least at this point.
So it's probably too soon to say with much confidence whether we'll see a change back to a more wintry pattern later this month.
Discussion of today's forecast
This 9:45 a.m. satellite water vapor image gives us a look at the flows creating our unseasonably balmy weather:
1. We always look first upstream, and here we see the feature that's going to make things rather windy by mid-week. The arrows show counter-clockwise circulation around a fairly deep, cold low over the Gulf of Alaska. This low is supposed to ride over the top of the ridge and down its eastern side by late Tuesday, sluicing the cold air into the Great Basin that will tighten surface pressure gradients and kick up another around of wind.
2. 150-knot polar jet flowing over the top of the eastern Pacific ridge. The low is, in fact, causing the jet to buckle and bulge north over the west coast, while shoving this giant atmospheric rumple toward northern California. So the upshot for us, today, is our warmest day of 2008 so far, I think.
3. I marked the ridge with an "H." This is warm air, flowing clockwise and therefore sinking, drying and warming even more. This warm air is approaching us today from the west.
Skies are already mostly clear over northern California, except for some fog trapped in mountain basins and some thin milky-white high clouds -- all signs of a stable atmosphere. The fog is still visible along the Trinity River in this 10 a.m. satellite image:
Surface charts show high pressure building over eastern Oregon as cold air rushes in from western Canada into the trough created by the low that moved through the Pacific Northwest yesterday.
(By the way, the front at the leading edge of this low fanned some fairly thick cirrus into north state skies yesterday afternoon, keeping a bit of a lid on top temps around the northern valley).
This building surface high has created a bit of a pressure gradient into far northern California that's feeding gusty north winds around Redding and environs this morning. Here's the gradient as of 9 a.m.:
Wind gusts at the Redding Airport have already hit 18 mph. These winds could blow a bit harder as the morning goes on, but they should ease through the afternoon as the surface high moves east with the approaching ridge, which will spread warm air aloft inland and ease the pressure gradient.
Meanwhile, these winds will be blowing down slope and warming adiabatically, or through compression. I think they'll contribute generously to today's proto-vernal warmth.
This chart depicts the upper air and surface patterns forecast by the GFS for 4 p.m. today:
The approaching ridge is clearly visible in the warm colors washing over northern California. The yellow-orange represents 500 mb heights in the 576-to-582 decameter range. Those are nearly summer-like 500 mb height levels, and they are way, way above the 561-decameter average for this time of year over the north state.
Remember that 500 mb heights are proportional to air mass temperature, since warmer air is more expansive (the molecules in it are bouncing around more, like a mosh pit) and bulges farther into space.
Forecast temperatures at the 850 mb level also indicate a warm afternoon. Temps at that level are forecast to poke up to 11 degrees C by 4 p.m. Air that warm mixed adiabatically to the surface would yield top temp of 75 degrees, which is what I went for today. An that forecast may prove too conservative!
None of the other forecasters predict anything that warm as of this morning, or at least not the last time I checked. But all of us Weather Geeks do revise our predictions from time to time, especially when reality is proving them wrong.
The Redding Airport was already up to 63 degrees just before 10 a.m. I'd say those forecast highs in the mid-60s for this afternoon are in serious jeopardy of slight inaccuracy -- not that anyone really cares (mid-60s, mid-70s, it's all pretty nice if you like warm sunshine and a drag if you don't).
Posted by I.M.Basking at February 12, 2008 7:32 AM
It seems we get a warm stretch in the middle of Feb.every year. But then winter returns and we are plunged back into reality. I'll enjoy it while it lasts.
Nice going
Rest of today
68 degrees
Sunshine sometimes filtered through high clouds
Light variable winds, turning north to 8 mph after dark
Sunshine sometimes filtered through high clouds
North wind to 10 mph
Rest of this week: Cooler and windy Wednesday into Thursday, then back to early spring
Mid-range models now show a much stronger, warmer ridge holding over California this week. That means continued unseasonable warmth -- heck, you might as well say it's early spring.
So we'll see another mild day Tuesday, from the way things look now.
A rather energetic short wave trough still looks likely to dimple this ridge by mid-week. But forecasts are more emphatic than ever that the ridge will just shunt this wave off to our east, where it will sink well into the Great Basin and create a steep pressure gradient up and down California.
Anyone Geeky enough to follow these discussions when the weather is this boring knows what a shot of cold air into the Great Basin means on the ground: a round of gusty, frankly annoying north winds that will start cranking up Wednesday and blow into Thursday morning. We'll probably see wind gusts approaching 40 mph, from the look of the gradient as forecast for several days now.
These winds should ease by Thursday afternoon. Afternoon temps will probably pop back into the upper-60s and even low-70s around the far northern Sac Valley by Thursday if not Friday, and stay there through next weekend.
Next week and a bit beyond: Looks mostly dry
Last week's longer-range forecasts indicated a wet pattern might return by next week. Now it looks like that idea is on hold for awhile. We could well enjoy, if that's the right word for it, another week of unseasonable warmth -- although a tail end of a trough could depress temps a little and even spread a shower threat into the north state around Wednesday, Feb. 20.
The long-range GFS (Global Forecast System) still shows the polar westerlies going zonal and sagging south, but now not until about Feb. 24, which is way the heck out there and a date not to be filed away as a sure thing for a big pattern change.
Rest assured, though, the pattern eventually will change. There's apparently lots of complicated stuff happening in the tropics that will, somehow, in a very non-linear but elastically Rube Goldberg manner, send more cold, wet storms our way -- perhaps before month's end, or at least by early March.
Discussion of today's forecast
This 9:15 a.m. satellite water vapor image gives us a quick look at the flow creating this ongoing early spring-like weather over much of California:
1. Yet another low plowing into the British Columbia coast just north of Vancouver Island.
2. This low has created a shallow trough that's pushing a weak cold front through the Pacific Northwest as it heads east.
The trough is basically a big bag of cold air, and as such, it's diluted the bulge of warm air over California, essentially mowing off the top of the ridge that's made the past couple of days so vernal. But the warm air, or the ridge, should surge back behind the trough.
3. The ridge, which I marked with an "H." Air is flowing clockwise around the ridge, and clockwise air generally leads to sinking motions in the atmosphere, and sinking motions generally dissolve clouds and discourage precip, since air that is sinking warms with the increasing pressure and warming air with no moisture added will evaporate whatever moisture remains. Hence, our mostly clear skies.
The hump or axis of this ridge looks likely to move east, toward us, over the next 24 hours, bringing more early-season warmth.
Clouds geneated by the front to our northwest look impressive on this 9 a.m. satellite image:
But radar shows only scattered light showers through western Washington and Oregon.
This 9:15 a.m. close up shows the cloudiness off the Redwood Coast and just a band passing overhead that will drift south of our area by the time I post this stuff:
Other than a few more high and middle clouds bleeding off the front to our north from time to time, we should see lots of sunshine today.
This GFS depiction of surface and upper-air patterns at 4 p.m. today shows ridging off the coast amping up a little as the trough moves east:
The color contours represent 500 mb heights, which are proportional to air mass temerature. The ridge off the coast is clearly visible with the swelling of warm colors, which indicate higher 500 mb heights and warmer air, since warmer air is more expansive than cold and, literally, bulges higher into space.
The yellow contour running northwest-to-southeast over California represents 500 mb heights in the 570-to-576-decameter range, which is well above the 651 decameters normal for this time of year. These heights are comparable to what we've seen the past couple of days, when afternoon temps have wafted into the upper-mid-60s and, yesterday, the low 70s in many places.
There's some indication that today won't be quite as warm as yesterday, however. We're starting the day off a couple degrees colder, and we're not getting the warming down slope winds that never quite died off yesterday, contrary to my forecast.
Meanwhile, forecast 850 mb temperatures are a couple degrees C cooler this afternoon than yesterday afternoon, thanks perhaps to the trough to the north turning the flow somewhat northwest and mixing in cooler air.
I'm not super-confident about today's top temperature forecast hitting the precise mark. But I am fairly sure we'll wind up somewhere in the mid-to-upper 60s, not quite matching yesterday's low 70s.
Looking good
It looks like we'll enjoy unseasonably mild weather all weekend through Monday before things turn cooler Tuesday, and then downright windy Wednesday and Thursday for reasons I've discussed in prior posts.
Spring-like weather should return Friday and hang through next weekend into the following week, from the look of things now.
Longer-range forecasts had suggested a wet pattern returning the week after next. But now it looks like the wet weather, if it comes at all, may go to our south.
Back to today and Sunday: top temps could again waft into the mid-to-upper-mid-60s in many places around the far northern Sac Valley as warm air aloft stays over California.
It looks like the north wind may die off by afternoon as surface pressure equalizes across the interior west with a more zonal flow aloft. So we may not get quite as much adiabatic warming, and that could shave a degree or two or three off today's top temp.
And we'll likely see more high clouds filter in, especially later in the afternoon as an approaching low over the Pacific Northwest steamrolls the ridge and bleeds moisture south.
Sunday could wind up warmer and sunnier than I had expected, since the ridge seems likely to bounce back once the low shoves off to the northeast.
Early morning temps tomorrow could well wind up lower than today's, however -- close to freezing or even below in the most sheltered spots -- provided the wind dies off, as expected. But the far northern valley could drift back into the lower-mid-60s or higher by afternoon as warm air aloft once again surges up from the south in the anti-cyclonic flow.
That's all the discussion and analysis I can do today, given a front-loaded early morning schedule in my real job as an R-S reporter. I'll try for a full forecast and discussion tomorrow (Sunday).
More than "a tad" warmer
The Redding Airport topped out at 67 degrees today. That's 10 degrees warmer than yesterday and well above the 59-degree normal for the date.
I had thought today would go over 60 degrees. But I obviously underestimated the warmth provided by the approaching ridge and relatively benign down slope winds.
Here are some other top temps today from around the far northern Sac Valley, courtesy of the Mesonet:
Southwest Redding (Girvan Road area): 72 degrees
Enterprise (Victor and Derby): 68.5 degrees
North-central Redding (Upper Hilltop): 67 degrees
Palo Cedro (Deschutes and Swede Creek roads): 65 degrees
Shasta Lake (Pine Grove): 65 degrees
If you enjoy this weather, expect more of the same tomorrow before somewhat cooler air filters in Sunday.
Today's warmth was far from the record books. The Redding Airport hit 80 degrees on this day in 2006.
Our collective memories associate that winter with one long dreary chilly sog-fest. But like all winters, 2006 featured dry spells and unseasonable warmth (although I don't think Redding saw 80 degrees again that year until late April).
Maybe a tad warmer
Rest of today
61 degrees
Sunshine sometimes filtered through high clouds
North wind to 15 mph with higher gusts
Sunshine sometimes filtered through high clouds
North wind to 10 mph, becoming light and variable afternoon
Next week: No longer looks so warm, but north winds still a good bet mid-week
Mid-range models have turned bearish on the idea of a big warm air dome sitting just off the west coast much of the week, giving the north state an early dose of spring.
Monday still looks rather mild after a slight cool-down on Sunday. Top temps could easily poke back toward the mid-60s.
But then the first of a couple of weak waves approaches Tuesday. There's an outside chance the trough of this first wave could dip far enough south to spread light showers into the mountains north of Lake Shasta -- and possibly into the far northern Sac Valley -- that evening.
Even if this wave doesn't bring any rain or snow, it's almost certain to sluice a shot of cold air into the Great Basin that tightens the pressure gradient and gins up gusty north to northeast winds over the northern valley Wednesday into Thursday.
Ridging bounces back by Thursday afternoon -- though not for long.
Forecasts now suggest the polar westerlies will ripple another wave across the Pacific Northwest into far northern California on Friday, and heights will stay relatively low into Saturday, for coolish top temps.
This second wave doesn't look like a big rain producer either. It will just spread enough cool air to kibosh the mid-winter warm spell that looked possible just yesterday.
Week of Feb. 17 - 23: Some precip possible early in the week, followed by another north wind -- nothing too exciting, in other words
The long-range GFS (Global Forecast System) continues to suggest the polar jet will turn zonal and sag south around Feb. 17 (week from Sunday) through about Feb. 20, delivering several fast-moving waves that could bring some rain and snow to the north state.
The Ensemble Mean is also suggesting better rain and snow chances over northern California early the week after next, although the prospects aren't exactly impressive.
The GFS indicates westerlies will amp up after mid week. The next wave to approach the coast looks like it could split and wash out, not bringing us any more precip. Instead, we'd see another round of gusty north winds Feb. 23.
Discussion of today's forecast
This 9:15 a.m. satellite water vapor image gives us an overview of the pattern and the various flows creating our lovely boring weather:
1. A low modeled at 982 mb is shoving the ridge that's sat off the coast all week inland toward northern California today. This low will also steamroll the ridge, however.
2. This rather high-amplitude ridge is so beautifully visible in the water vapor image I did not want to muck it up with a bunch of arrows.
The one arrow is supposed to show the steady eastward movement of this ridge over the next 36 hours. I could have drawn another arrow to show how the Gulf of Alaska low will mash this ridge, so by the time its axis crosses northern California, it won't be nearly so lofty and full of warm air.
Surface maps show a nose of higher pressure poking in along the Oregon border with this ridge. The higher surface pressure to our northwest has created a slight gradient and sparked a light north wind this morning.
These winds will probably pick up later and could get a little gusty as pressure builds and sunshine creates convection that stirs up the boundary layer. Air moving down slope with these winds will likely goose our afternoon temperatures, since the flow will be warming with compression.
3. Clockwise flow in the high pressure, warmer-air dome approaching the coast is still pulling down high-level moisture flowing through the polar westerlies, sort of the way you pick off wads of cotton candy off the cardboard stem.
So even though warming, sinking, drying air is moving in, thin high clouds are muting the sunshine over the valley while thicker clouds cover the mountains. These clouds could blunt our sunshine and limit warming somewhat.
The high clouds over the valley are barely visible in this 9:45 a.m. satellite image, though the thicker clouds above southern Oregon and Siskiyou County are certainly evident:
I expect fewer clouds as the day goes on, since the ridge will be moving inland, pushing the moisture band east, as this GFS depiction of the pattern forecast for 4 p.m. suggests:
The ridge is clearly visible in the bulge of the color contours. The ridge axis is just off the coast by 4 p.m. We're still under a relatively cool northwest flow down the front of the ridge, but with the axis that close, we'll be feeling more the effect of the warm air bulging up in the ridge.
The yellow contour represents 500 mb pressure heights in the 570-to-576-decameter range. Remember that 500 mb heights are roughly proportional to air mass temperature, since warmer air, being less dense, bulges farther into space.
500 mb heights over far northern California average around 561 decameters at this time of year, so the atmosphere will be much warmer than normal -- at least aloft. Combine that with warming from down slope winds, and the potential is certainly there for our warmest afternoon in three weeks.
No forecaster I reviewed this morning was willing to predict Redding would crack 60 degrees. I went out on a bit of a limb and predicted 61 degrees. But that forecast could be too conservative, too. We could hit the mid-60s -- though the high clouds could wind up keeping temperatures lower.
It's a tough but, in the end, not terribly important call.
Not exactly a conversation starter
Rest of today
56 degrees
Variable cloudiness with haze
South wind to 8 mph, shifting north
Becoming mostly sunny by mid-morning
North wind to 10 mph, becoming light and variable afternoon
The weekend: Fine for outdoors
Expect more of the same -- cool mornings and mildish, hazy afternoons. Not bad.
Next week: Warmer and sometimes breezy
Mid-range forecasts continue to show the ridge building amplitude by Monday for somewhat warmer afternoon temps, perhaps well into the 60s.
A weak wave flows over the top of this ridge Tuesday into the Great Basin, where the shot of cold air could tighten pressure gradients and kick off a round of dry, gusty north winds.
These north winds could blow Wednesday into Thursday, possibly pumping up temperatures Thursday afternoon into the 70s.
By Friday, a fairly deep low in the Gulf of Alaska carves out a trough that dips far enough to possibly cool things down and cloud things up -- but not deep enough to bring significant rain and snow to the north state. All of the precip looks likely to stay north of the Oregon border.
We could see a coolish, breezy day next Saturday in the wake of that wave.
Week of Feb. 17 - 23: Possibly unsettled
Longer-range forecasts still suggest more active weather across the west coast. The GFS (Global Forecast System) continues to show a series of deeper waves hitting northern California Feb. 18 - 20. But the Ensemble Mean shows a flatter pattern with stronger precip signals over the Pacific Northwest.
Bottom line: it's too soon to tell what will happen after mid-month.
Discussion of today's forecast
Surface charts show a weak and disintegrating low over southern British Columbia trailing a cold front whose ragged southern end is draped across far northwestern California.
This front has spread clouds across the north state down into south-central Shasta County, but hasn't dropped significant precip. Radar has picked up only a few faint echoes this morning.
This 10:15 a.m. satellite image shows the clouds associated with the front across Oregon into far northern California:
If you look closely at this pattern, you can pick up the slight wave pattern bending the cloud band from the northwest toward the southeast as it approaches the coast. This is the northwest flow down the front or eastern side of the ridge off shore.
Here's a closer view of the cloudiness over far northern California, as of 10:45 a.m.:
Here we see clouds mainly over the mountains and clearing across the valley. This clearing is a sign of a relatively dry and stable atmosphere. The mountains force air in the northwest flow to rise, cool adiabatically and condense. But once that air sinks, following the topography, it warms adiabatically (with increasing atmospheric pressure at lower altitudes), dries out and erodes the cloudiness.
I analyzed the flows creating this pattern on this 10:15 a.m. satellite water vapor image:
This image shows the ridge-trough pattern across the eastern Pacific much more clearly than the visible satellite.
I marked the ridge with an "H". Forecasts indicate this ridge will migrate toward the coast over the next 36 hours, creating warmer and clearer weather tomorrow afternoon. The ridge weakens and flattens by Saturday.
But back to today:
1. Cool-to-cold air creating the trough over the Gulf of Alaska, east of the ridge.
2. 170-knot jet blowing down into the base of the trough, into the Pacific Northwest.
3. Water vapor imagery suggests the low, or what's left of it, sits over Idaho. But surface charts locate it much farther northwest.
The GFS suggests little change from yesterday or the day before in the upper-air and surface patterns by 4 p.m. today:
The ridge-trough pattern is again clearly visible in the color contours describing upper air flows, as is our place in the "no-mans land" between the two. So we're in for more bland tweener weather.
The black lines, which represent surface pressure, suggest light gradients across northern California. The surface high over the eastern Pacific begins to approach the coast, creating a wind shift to the north by afternoon.
Perhaps these winds will be just strong enough to clear a bit of the haze. I doubt they'll contribute much to our afternoon temperatures, though I could be wrong about that.
I went with another persistence forecast, given the static air flow and little expected change in 850 mb temperatures.
Mid-winter stagnation
Rest of today
55 degrees
Variable cloudiness with haze
South wind to 8 mph
Variable cloudiness with haze
Slight chance of showers morning, mainly mountains
South wind to 8 mph
Friday and the weekend: Looks quiet
The somewhat stagnant, seasonably mild weather looks likely to stretch through the weekend. Expect chilly early mornings (mid-30s) and afternoons wafting toward the lower 60s.
A weak wave might ripple through the Pacific Northwest on Saturday, mixing in just enough cooler air to slightly depress temps and spread out a few more sheet-like clouds.
Next week: Stirrings of spring?
Mid-range forecasts show the flat ridge holding over California. Such areas of sinking, drying air are storm-hostile, so we would not see much significant weather all week, should the forecast verify.
500 mb heights look like they'll hit an early peak Monday, when surface temps could waft well into the 60s, inspiring the first stirrings of spring.
A wave dimples the ridge by Tuesday afternoon. This wave will pass to our northeast, dropping temps, tightening the pressure gradient and ginning up the north wind. Tuesday and especially Wednesday could be rather breezy.
It's worth noting the Canadian is much more bullish with this wave, digging it down the coast where it sops up enough moisture to douse us with some showers. That's an outlier forecast right now, however.
Warmer, calmer air bulges back in with an even stronger eastern Pacific ridge starting Thursday, from the look of things.
We could see the young vernal season's first 70-degree-plus afternoon next Thursday or Friday. If the fruit trees aren't blossoming already, they'll start then.
Week of Feb. 17 - 23: Wet pattern may return
The long-range GFS (Global Forecast System) suggests an energetic polar jet may again sag south and aim some Pacific moisture at northern California. The model shows two fairly deep waves crossing the north state around Feb. 18 - 19.
The usual caveat applies -- it's way too soon to bank on something so far out on the forecasting horizon. It's just a possibility to watch.
Discussion of today's forecast
The north state sits between a huge high pressure mound over the east-central Pacific and a deep, turbulent trough over the Midwest. All of the active weather is well to our north and east.
I analyzed the pattern on this 9:45 a.m. satellite water vapor image:
1. A developing low in the Gulf of Alaska. This low, like the one that moved through the Pacific Northwest yesterday, is supposed to stay well to our north and not dig a very deep wave. So the front at the leading edge of the trough created by this low will barely clip far northern California later tonight into tomorrow morning. We probably won't even squeeze out a drop.
2. The jet feeding this low is mostly zonal, or flat west-to-east -- again showing the lack of amplitude in the wave pattern. This would be a wicked winter situation for us if this jet, which is screaming along at about 190 knots, were aimed at California. But it's not -- and the jet isn't supposed to slip south any time soon.
3. Flow aloft over California is from the northwest, or clockwise around the eastern side of the huge high over the Pacific. Northwest flow tends to bring somewhat cooler-than-normal weather. And in this case, the northwest flow is continuing to pinch off moisture flowing into the Pacific Northwest and send it across northern California.
4. The deep, cold trough over the Great Basin, Rockies and Plains. That was our stormy weather last week. Now it's stirring up deadly tornadoes in the South, on the active, eastern side of the trough.
This 9:45 a.m. satellite image shows the bulk of the clouds along the west coast flowing into the Pacific Northwest, with far northern California just at the fringes:
This closer view of northern California as of 10:00 a.m. shows some ground fog in the central Sac Valley and mainly high cloudiness, if any at all, over the northern valley and surrounding mountains:
The satellite image doesn't reflect how funky our air is this morning. We have to look well over the horizon for an explanation, to that low developing in the Gulf of Alaska near the Aleutian Islands.
This low is the closest thing to us creating any kind of pressure gradient. So we're getting a sluggish flow from the south into this low center, over 1,000 miles away. The up-valley flow is full of marine moisture and agricultural funk, which is trapped against the mountain horseshoe around the far northern Sac Valley.
The GFS depiction for the patterns at the surface and aloft show little change as of 4 p.m.:
The huge ridge over the Pacific and the deep trough over the Midwest are both clearly visible on the color contours. These contours slope northwest-to-southeast over California -- our cool northwest flow.
Virtually no black lines, or isobars, cross the state, which suggests pressure gradients are nearly flat and winds will continue sluggish. We sit in a "saddle" between surface highs to our west and east, though we're close enough to the developing low in the Gulf of Alaska to see continuing wind out of the south into that low. So more haze seems like a good bet.
Forecast heights aloft, 850 mb temperatures, variable cloudiness and up-valley flow have changed little over the last 24 hours. So I'm going with a persistence forecast, expecting continued slightly-below-normal afternoon temps in the mid-50s much like yesterday's and probably much like tomorrow's.
Rain check: January and season-to-date
Here are preliminary January precipitation totals for selected north state spots courtesy of the California Department of Water Resources, the National Weather Service and the Citizen Weather Observer Program. Totals are in inches:
Brandy Creek: 22.20
Hillcrest (Hatchet Mountain): 17.60
Shasta Dam: 17.04
Summit City (Shasta Lake): 16.24
Upper Hilltop (north-central Redding): 13.39
Fire Station 2 (west Redding): 13.12
Girvan Road area (southwest Redding): 13.05
Deschutes and Swede Creek (Palo Cedro): 12.19
Diddy Wells (Highway 299 East): 12.08
Victor and Derby (Enterprise): 12.08
Hayfork: 10.99
Hacienda Heights (northeast Redding): 10.08
Mount Shasta: 10.07
Redding Airport: 9.98
Shingletown: 9.80
Chico: 7.14
Red Bluff: 6.83
Here are preliminary season-to-date totals for selected north state spots. The rainfall season begins July 1. Totals are in inches:
Hillcrest (Hatchet Mountain): 40.61
Brandy Creek: 39.81
Shasta Dam: 33.45
Summit City (Shasta Lake): 32.55*
Fire Station 2 (west Redding): 30.45
Upper Hilltop (north-central Redding): 28.89
Diddy Wells (Highway 299 East): 27.17
Victor and Derby (Enterprise): 26.88
Hacienda Heights (northeast Redding): 23.79
Hayfork: 23.13
Mount Shasta: 22.37
Shingletown: 21.52
Redding Airport: 20.75
Chico: 15.80
Red Bluff: 12.59
*Through Jan. 31
Here are a few comparisons between season-to-date and normal-to-date for selected north state spots. Totals are in inches through today:
Mount Shasta
Season-to-date: 22.37
Normal-to-date: 21.53
Shasta Dam
Season-to-date: 33.45
Normal-to-date: 37.97
Redding Airport
Season-to-date: 20.75
Normal-to-date: 19.18
Red Bluff
Season-to-date: 12.59
Normal-to-date: 14.18
Back to boring
Rest of today
54 degrees
Variable cloudiness
Showers possible in the mountains tonight
Chance of light showers in the valley
Snow level around 4,000 feet
North wind to 8 mph, becoming light
Slight chance of showers in the morning
Snow level around 4,000 feet
South wind to 5 mph
Rest of this week: Uneventful
A long series of unusually cold winter storms has left one of the deepest snow packs in recent memory around far northern California.
Now that snow pack will have a chance to settled over the next week or so, while the valley will continue to dry out.
The hemispheric pattern that allowed these storms to feast on potent brew of Siberian and subtropical air the past couple of weeks has shifted just enough so the polar jet is now aiming mostly at the Pacific Northwest.
In other words, California is again sitting on the front side of a broad ridge over the central eastern Pacific. We'll get, at best, only a glancing blow from any incoming waves.
After tonight, another such wave could clip far northwestern California early Thursday. Once again, light precip looks possible for the mountains around the far northern Sac Valley, but marginal for the valley itself.
Next week and beyond: More fair than foul
Longer-range models show ridging off the west coast at least through mid-month. But a low plowing over the top of that ridge could trail a front whose southern fringes just brush the north state, again bringing better precip chances to the mountains around the valley than the valley itself around Tuesday, Feb. 12.
A stronger front looks possible on Sunday, Feb. 16. Even so, it would hardly match any of the recent storms.
Otherwise, far northern California would enjoy mostly fair, seasonably cool to mild weather punctuated by mostly light winds for the foreseeable future.
Discussion of today's forecast
Surface maps and satellite images show a garden variety cold front off the coast, trailing from a 979 mb low in the Gulf of Alaska approaching the British Columbia coast just north of Vancouver Island.
The front parallels the Pacific Northwest coast and then bends off to the southwest, away from the California coast.
The wave driving this front through is fairly shallow -- perhaps because it's had to do lots of work squashing the ridge keeping California dry the past couple days. And the ridge is still squatting there, deflecting the wave north. So there's not going to be lots of energy or moisture left to deliver much in the way of precip with this front.
This 10:15 a.m. satellite image shows the front off the coast:
The high cloudiness we're seeing this morning isn't exactly a product of this front, which is still well off shore. It's just moisture pulled down from the flow into the Pacific Northwest in the clockwise circulation in the ridge, which is from the northwest over us right now.
This 10:45 a.m. satellite image shows these clouds, which are really just passing through. We'll get more sunshine later this morning well into afternoon before the front's cloud shield approaches:
I analyzed the flows producing today's weather on this 10:15 a.m. satellite water vapor image:
1. Counter-clockwise circulation around the low off Vancouver Island. We can get significant weather from lows this far north, but in today's case, the low had carved out a rather shallow trough, so the cold front at the leading edge of this trough is having trouble reaching this far south.
2. 170-knot jet on the back side of the trough. Again, the flow is a little more zonal than we've seen, so the trough isn't as amped up and digging quite as deep, which means only an outside shot of some light precip for us.
3. The front approaching Oregon and Washington. It's not a terribly impressive front and it's going over the top of the flat ridging over California.
4. Clockwise flow in the ridge over California. Given the ridge axis to our west, the flow over us is from the northwest. This northwest flow is directing coolish air and some cloudiness over northern California, but not much other weather.
Here's how the GFS (Global Forecast System) depicts the pressure patterns aloft and at the surface as of 4 p.m.:
We can see the low has pushed into British Columbia by this. The color contours show only a slight trough over the Pacific Northwest, and the colder air concentrated over Washington State. California still sits under coolish northwest flow uner the broad ridging across the central eastern Pacific which has shunted the storm track north.
The black lines on the chart represent isobars, or lines of equal surface pressure. Isobars are key to predicting wind direction and strength.
This afternoon's chart shows no strong pressure gradients over northern California. The gradient into the low over British Columbia only reaches into southern Oregon, while the surface high off the coast is fairly modest. So winds should stay light all day.
The coolish northwest flow aloft with occasional cloudiness ought to keep afternoon temps in the seasonable mid-50s. I may have erred a bit, predicting lower-mid 50s when we could well wind up in the upper-mid-50s. It's not a huge deal.