Cold Air Coming

James has discussed the Arctic Oscillation Index (AO) lately, as we did during late December in anticipation of the major cold outbreak in early January. Basically, a negative AO means that pressures are below normal in the Arctic, and generally above normal in midlatitudes (like the US and Europe), meaning cold air displaced southward from the Arctic. Here is the AO lately, and the Ensemble forecasts through February 16.

Notice that the models predict a negative AO again in early February. Take a look at the GFS ensemble mean 850 mb (low level) temperature anomaly from normal (in degrees C) over the next 10 days.

This indicates cold air moving in again starting this weekend, and getting colder next week. The GFS is the most aggressive with the cold air, but the models are in agreement that we’ll see another cold outbreak, not as intense as the one in January, over the next 2 weeks. It’s not like we’ve been warm much anyway.

December 2009 was the 23rd coldest on record in BHM since 1896, with an average temperature of 43 degrees, 3.1 degrees below normal. January 2010 was the 14th coldest with 38.9, 5.7 degrees below normal. When you combine December and January, this winter has so far been the 12th coldest on record. If below normal temperatures continue through February, this could be our coldest winter since 1983-84, and one of the top 10 coldest.

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