Tuesday, December 14, 2010

La Niña and Winter 2010-11 Circulation Outlook

A moderate to strong La Niña currently exists in the Pacific Ocean and it should persist through Spring 2011. It is expected that it will play a significant role in the weather patterns during the Winter of 2010-11.

As noted on the map to the left, the primary jet stream is deflected well to the north with persistent heavy rains and snows in the Pacific Northwest of the U.S. and Canada. With Gulf moisture shut off and most of the storm systems entering the Pacific Northwest, drier than normal weather is expected across the SW and Southern U.S. Cold air will accumulate in western Canada and from time to time plunge into the lower 48 states, bringing spells of well below normal temperatures to the Midwest followed by rapid warm ups after each polar plunge. This circulation pattern should produce a "roller coaster' temperature cycle of large swings between well below normal temperatures and above normal temperatures throughout the Winter for much of the Midwest and Great Plains.

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