Thursday, December 20, 2012

A Cold, Stormy End to the Year?

Surface map at 6:00 p.m. CST December 20
The intense low that brought blizzard conditions to parts of the central U.S. and severe thunderstorms and tornadoes to the south is moving through the Great Lakes tonight. The footprint of this winter storm covers the entire country east of the Mississippi River tonight.  Does this storm mark the start of a change in the winter weather pattern? It very well might.

The medium range models are still indicating a change in the upper level pattern in the next week to ten days along the lines of that shown in my December 17th post. The cold air is still bottled up in Alaska and northwest Canada. Fairbanks, for example, just experienced its sixth day in a row with lows -40F or lower and the warmest highs just reaching -19F. It appears that this cold air may be dislodged in the next week or so as an upper level  ridge builds in the eastern Pacific and a trough develops across the U.S.  Both the 6 to 10-day and 8 to 14-day outlooks issued today by the NWS Climate Prediction Center are indicating a higher probability for below normal temperatures across much of the country.

In addition, a series of low pressure systems moving across the U.S. in the next 10 days will likely produce precipitation in the Great Basin and/or the eastern half of the country.

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