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Weather Underground Forecast for Wednesday, December 09, 2009.

The winter storm over the Central and Eastern US is expected to amplify on Wednesday. As the system pushes eastward into the Mississippi River Valley, the system will scoop up a minor trough lingering over the Gulf states and strengthen as it obtains additional moisture. This system will create a double frontal boundary, with one strong cold front followed closely by a second, that will sweep from the Central Plains, over the Mississippi Valley, and approach the East Coast. This system will extend well northward into the Great Lakes, where it will continue bringing periods of heavy snowfall. Winter weather and blizzard advisories will remain in effect over the Midwest as snowfall rates will vary between 1-2 inches per hour and wind gusts up to 29 mph over the Upper and Mid-Mississippi Valley. The Upper Midwest and Great Lakes region will see new snowfall between 1-3 inches, while New England and the Northeast will see increasing snowfall with totals less than a half of an inch. To the South, above-freezing temperatures will allow for periods of heavy rain associated with late season thunderstorm development. Expect a messy combination of sleet and frozen rain between these regions, in the Tennessee and Ohio Valleys. Take extreme caution when driving and traveling under these weather conditions.

Behind this system, expect cold air to continue pouring in from Canada. This will allow for extremely cold temperatures over the Northern and Central Plains with wind chills allowing for below-zero high temperatures. Breezy conditions are anticipated over most of the Rockies and Central US.

Further West, a trough of low pressure off the West Cost will push moisture over California and allow for another rainy and cool day. Highs will remain in the 40s and 50s across the West Coast.

Temperatures in the Lower 48 states Tuesday ranged from a low of -34 degrees at Havre, Mont. to a high of 89 degrees at Punta Gorda, Fla.