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Forecasters predict tough winter ahead
The AccuWeather.com Long-Range Forecasting Team reported that while the worst of winter will be focused over the Midwest and Northwest, it does not mean other parts of the country are off the hook.
A weak to moderate La Niña is a key factor in the 2011-2012 Winter Forecast with more typical La Nina winter conditions expected.
"La Niña, a phenomenon that occurs when sea surface temperatures across the equatorial central and eastern Pacific are below normal, is what made last year's winter so awful for the Midwest and Northeast," AccuWeather.com Meteorologist Heather Buchman stated in the initial release of the 2011-2012 Winter Forecast.
La Niña winters feature a stronger Northern jet stream, an area of strong winds high above the Earth's surface. This positioning and strength of the jet stream tends to cause storms to track across the northern tier, spelling harsh winters from the Northern Plains to the Ohio Valley.
Typically, the southern tier of the U.S. ends up mild and dry in a La Niña winter. There will be some exceptions to that this year with wet weather anticipated for parts of the Lower Mississippi Valley.
Another big factor in the winter forecast is the potential for a blocking pattern to develop with the NAO, or North Atlantic Oscillation, possibly turning negative for a time. This essentially means that a large area of high pressure could set up over Greenland, forcing cold blasts to reach the U.S.
"The lack of sea ice has been believed to contribute to the development of blocking. This past summer and early fall, sea ice reached near-record low levels," according to the National Snow and Ice Data Center.
Paul Pastelok and the Long-Range Forecasting Team that he leads still think Old Man Winter will leave the biggest impression on the northern Rockies, northern Plains and the Midwest.
It will be a snowier-than-usual season for the Midwest, which will lie to the north and west of the frequent storm track, or in the "sweet spot" of the storms.
Typical of a La Niña year, the harshest cold will blast the northern Plains and northern Rockies.
Winter looking wetter for California, still stormy for Northwest
The 2011-2012 Winter Forecast was updated to show even more rain and snow for northern and central California with the Pacific jet stream expected to hover over this area for most of the winter season.
Farther inland, this winter is expected to be another active one for the northern Sierra and interior Northwest with above-normal snowfall forecast.
In contrast, the Pacific Northwest, including much of Washington and western Oregon, will get some breaks from the wet weather.
"Watch for a 'Pineapple Connection' during the mid- to late season that will send some areas well above-normal precipitation," Pastelok said. This means "snow in the mountains and rain and mudslides in the valleys."
Also known as the "Pineapple Express," the Pineapple Connection is a phenomenon that occurs when a strong, persistent flow of tropical moisture sets up from the Hawaiian islands to the West Coast of the U.S. This phenomenon often leads to excessive rain and incredible snow events.
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