Brett Anderson

New Forecast Model Clues about the Upcoming Winter

9/16/2011, 9:37:06 AM

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We just received the latest ECMWF model seasonal forecast output into our in-house system. I will focus on what the model is forecasting for the winter of 2011/2012.

By the way, the updated ECMWF is also supporting the latest thinking that weak to moderate La Nina conditions will return for the upcoming winter, and its new forecast for North America is certainly a reflection of that.

The key once again to the winter forecast could be the possible return to strong high pressure blocking over northeastern Canada. The latest ECMWF does not show this. Last year's ECMWF forecast for the winter under La Nina conditions showed northern latitude blocking, but it was underdone with the strength of the blocking during the first half of the winter and had it in the wrong area.

There are some recent studies which show that a lack of sea ice in the northern latitudes during the late fall and early winter causes wind patterns to change, resulting in more of a blocking pattern in the north, which can mess up the typical La Nina winter pattern that you would normally expect. This in turn forces more cold farther south into southern Ontario and the eastern U.S.

Whether or not this occurs once again this winter is still in question, but one thing we do know is that sea ice extent is very close to the record low minimum of 2007 as we speak, and I am pretty confident that the annual fall/early winter freeze-up will be weeks behind schedule once again. I expect well-below-normal sea ice extent over northern Canada at least into the first half of the winter.

If the blocking does not return, then the ECMWF forecast may end up being pretty close, especially for January and February. This would mean plenty of cold for western Canada, even to the B.C. coast more than usual. It would also mean a healthy amount of snow this winter from the southeastern Prairies through central Ontario and southern Quebec. The model is predicting a warm winter from the southern U.S. Plains to the Southeast U.S.

I will issue my own preliminary winter forecast in a couple of weeks. My final forecast will be issued late in October.

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Here is the overall jet stream pattern that the ECMWF model is predicting for the upcoming winter.

590x497_09151638_pattern

590x497_09151701_patternwinterpcp

590x497_09151707_patternwintertemp


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Questions? Feel free to drop me a question, and I will get back to you as soon as I can. Here is the link to my email.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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