Winter Delayed? Updated U.S. Winter Outlook Still Trending Milder Than Last Winter

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This morning we posted the weather forecast for Christmas Day and now we’ll follow up with an overall look at the contiguous U.S. through about the beginning of February. (Again, kudos to ImpactWeather StormWatch team manager Fred Schmude for producing this forecast.)  After that?  Current data suggests an increase in the amount of much colder air starting in the second or third week of January.

Houston, December 15, 2011 – Even though we are rapidly transitioning to another La Niña pattern this winter weather season, we are currently seeing a much different flow pattern over the Lower 48 this year compared to last.  Typically when the flow pattern slows down (last year’s pattern), the main storm track will shove much colder air southward resulting in periods of extreme cold and major winter storms over the Lower 48.  This year so far we have noticed a much faster flow pattern, which has resulted in a faster west to east wind pattern bringing in milder Pacific air resulting in less storminess over the Plains, Deep South and East.   The question now is will this trend continue and if there is a change, when will that occur?  Based on the latest available data we are noticing some subtle long range signals favoring a progressively slower flow pattern as we move into the main core of winter. [More about and La Niña and El Niño here and here.]

For the remainder of December the forecast calls for most of the colder than normal temperatures  to remain over the Rocky Mountain States and Great Plains with milder than normal temperatures over the Atlantic Seaboard.  Precipitation will remain above normal for the Southern Plains northeastward across the Mississippi Valley, Great Lakes and Northeast, while a noticeable dry bias will remain in place over a large part of the West Coast and Florida.   Due to the progressive flow pattern, the risk of a major winter storm will remain below normal over the Lower 48 through at least Christmas Day; however, there will be periods of significant snow, mainly centered over the Rockies and Plains, through the 3rd and 4th weeks of the month.

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The longer range outlook for January and February calls for the flow pattern to slow down favoring an increasing risk of Canadian and Arctic intrusions of very cold air across the Lower 48 and an increasing risk for several major winter storms across the Plains and eastern U.S.   The exact timing of the pattern change is still on the low side, but it does appear the first week of January could see a significant change.   Areas extending from the Northern Rockies through the Great Lakes and Northeast will likely see enhanced snowfall amounts during this time period.  Depending on how much cold air is forced southward, we could even see 1 or 2 significant winter weather events over the Southern Plains and Deep South.  Farther west, the main core of unsettled weather is forecast to be centered across the Pacific Northwest and adjacent parts of the Northern Rockies where several large scale winter storms are forecast to strike the area.  Temperatures are forecast to trend below normal over the northern Rockies and Plains and somewhat milder when compared to normal over a large part of the southern U.S. from Arizona to Alabama for the winter.  Near to slightly below normal temperatures are also expected from the Great Lakes to the Atlantic Seaboard from southern New England to Florida.

Finally, here is the Hazard Concerns outlook for the upcoming winter weather season.  The main areas of concern this winter weather season include:  a higher risk of stormy weather over the West Coast (mainly Jan-Mar), a higher risk of heavier than normal snowfall over the northern Rockies (mainly Jan-Mar), drought relief over the Southern Plains (mainly Dec-early Feb), an elevated risk for significant icing from the Central Plains to southern New England (mainly Jan-Feb), an elevated risk of a hard freeze on the immediate Gulf Coast (mainly Jan-Feb), and higher than normal snowfall from the Great Lakes to New England (mainly Jan-Apr).

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