National Weather Forecast for December 21,2013 from weatherunderground.com

Weather Underground Forecast for Saturday,December 21,2013

A very active weather system will trek across the central and eastern thirds of the country on Saturday, while an area of low pressure will bring wet weather to the Pacific Northwest.

A cold frontal boundary extending from Texas to the Great Lakes will trigger severe thunderstorms, freezing rain, and flash flooding across a handful of states. Severe thunderstorms will be possible across the lower Mississippi Valley, the Tennessee Valley and the Ohio Valley as a warm, muggy air mass from the Gulf of Mexico interacts with a cold, continental air mass from the north. These thunderstorms will supply enough precipitation to trigger flash flooding. Freezing rain will be possible in parts of Kansas, Missouri, Iowa and Illinois before an abundance of heavy snow pushes across the area.

A separate and much drier cold front will stretch from the Intermountain West to the western Great Lakes, as frigid conditions will spread across the northern Plains and upper Midwest. Meanwhile, a low pressure system over the eastern Great Lakes and Northeast will allow for freezing rain and snow to set up across parts of New York and northern New England.

Out west, a trough of low pressure will continue to provide showers to parts of Oregon and Washington, while snow showers will move across the Cascades and northern Rockies.