Weather Blog

The weather version of "Coke vs. Pepsi"

The weather version of "Coke vs. Pepsi"
It's not exactly like we're going to do a blind taste-test, but our latest forecasting models are squaring off against each other, each painting a vastly different scenario for a storm expected to strike sometime either Thursday afternoon or Thursday night.

Earlier forecast models were pretty consistent in showing a very strong storm -- as deep or even deeper than the Dec. 2006/Hanukah Eve storm, although central pressure is not the sole deciding factor in a windstorm's affect on a region -- coming ashore somewhere along the north coast or southern Vancouver Island Thursday night.

But now some have changed their tune, bringing in a much weaker storm farther south across the central coast, and having it come in Thursday afternoon instead of Thursday night. Meanwhile, the others are sticking to their guns of the stronger storm to the north during the night, although not quite as dire as before. You can see for yourself. Here is one model (the "WRF-GFS" for those who like to know), valid at 10 p.m., Thursday night (which would be the peak winds for Seattle in this scenario):

Note it has a very strong storm center at 972 mb just north of Vancouver, B.C.  This is classic case for strong winds in the Puget Sound region, although if you take this at face value, it's not showing quite as much difference in pressure as the Dec. 2006 storm, although still a very large one.

(This is where you can count the black lines between Bellingham and Portland. In this image, there's about 18 -- meaning a difference in pressure of 18 milibars between those two cities. This model has been forecasting around 17-20 over the past few runs. Anything over 15, I consider a good punch. Inauguration Day Storm was 21.5 and Hanukkah Eve was 23.2.  More recently, the storm Monday was measured at 15.0 at its peak.) Anyway, this scenario would spell out quite a few power outages.

It would also mean we stay on the warm side of the storm, which would translate to higher snow levels and possible river flooding.

Now, here's the "NAM-MM5" version, valid at 1 p.m. Thursday (the peak winds in this painted scenario):

This model shows a much weaker storm, about 994 mb, coming in around Kalaloch and crossing over Everett. That would spell little or no wind from Everett north, and some gusty winds in southwestern Washington and possibly into the Seattle area, but not as strong as the other version (note the black lines are not as bunched together).  This would mean more of a mountain snow event with snow levels under pass level  and some rain in the lowlands, but probably not very memorable once the storm passes.

(On my "to do" list sometime soon is to do a blog entry that highlights some of these model outputs and what they all mean. If only the weather could stop for a few days :) )

Anyway, the point of this is to spell out the challenges we face as weather forecasters.  We were stuck with a somewhat similar challenge on Dec. 14 when that whole arctic outbreak began -- models disagreed whether that first storm would go to our north, bringing rain and wind, or to our south, bringing lowland snow but no wind.

The majority of the models were leaning with the south solution and so that was what the public forecasts went with, causing a lowland snow forecast for that Thursday that canceled schools but busted when the storm indeed went north and we get the mostly-harmless rain and wind. (Imagine if the snow that did hit during the Friday a.m. commute -- the one that had people stranded on 520 -- had happened with a bunch of kids in school? This time around, we don't have the arctic air, so there is no lowland snow threat with either of these scenarios. It's either, will it be windy or not, and will it rain or snow at 5,000 feet.)

So here we are again, and once again, forecasts are going to likely lean toward the windier scenario for now because, even if the southerly track were ever to start to lean a bit more likely, would you be willing to bet people's lives and property that the windier scenario won't occur?  We are fortunate that we do still have another day here to get a better handle on it, but for now, better to err on the side of "be prepared" and if the wind fizzles, you're ready for the next one :)