El Nino vs. Snowfall-Updated

The Climate Prediction Center (www.cpc.ncep.noaa.gov) recently came out with an update on the recent El Nino that is occurring in the Pacific and the resulting impacts that it will have across the lower 48. The forecast for the strength of the El Nino in the eastern Pacific if pretty much in line with the previous forecasts with having it reach “moderate” strength with Sea Surface Temperature anomalies of around 1.5 degrees and lasting through the winter and into the middle of spring. This generally means that our temperatures over the winter season will have the best chance of being at or above normal. In terms of precipitation, it tends to lead to drier conditions for portions of the Midwest. The main question that everyone asks is, “Well, does that mean that we’re not going to have a snowy winter?” Recent trends during El Nino years say that we won’t have a snowy winter. Here are some stats at the two climate sites in northern Illinois at Chicago and Rockford and how much snow they’ve received in past El Nino winters...
29.8 (-6.8)
36.5 (+4.2)
20.0 (-16.6)
19.3 (-13.4)
35.2 (-1.4)
39.8 (+7.1)
24.9 (-11.7)
18.9 (-13.8)
32.9 (-3.7)
26.6 (-6.1)
26.6 (-10.0)
28.0 (-4.7)
42.6 (+6.0)
45.0 (+12.3)
28.4 (-8.2)
30.6 (-2.1)
24.1 (-12.5)
32.4 (-0.3)
29.6 (-7.0)
No Data
28.6 (-8.0)
18.3 (-14.3)
(Note: Since dealing with a larger dataset than the last 30 years, adjusted numbers to reflect the data from the entire dataset, which means data going back to 1884 for Chicago and back to 1906 for Rockford.  The latest 30 year normal may be skewed a bit by the large snowfall seasons of the late 1970s.  The overall averages were 1.4" lower for Chicago and 6.0" lower for Rockford when compared to the current 30 year normals provided by NCDC.)
So, it is pretty evident that in this 60+ year sample that an El Nino year tends to translate to below normal amounts of snowfall during the winter.  There are a few exceptions, so it isn’t entirely impossible to have an above normal season, but it does look rare.  So far for the snow season, Chicago has received 6.5” of snow, which is 2.0” above the normal value of 4.5” for up to this point in the season. At Rockford, 10.9” of snow has fallen so far this season, which is 5.7” above the normal value of 5.2”. Although we are above normal for this point in the season, the effects from El Nino aren’t typically felt until later in the winter season, so we’ll have to wait and see what happens!
Tim Halbach
Climate Focal Point
Updated 12/13/06

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