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Updated: 7:00 PM GMT on August 20, 2014
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Weather Underground Forecast for Wednesday, August 20, 2014

An area of low pressure will move across the Great Lakes on Wednesday, while a separate low pressure system will dip southward over the northern Plains.

A low pressure system will begin to dip south southeastward over the northern Plains on Wednesday. As this system interacts with warm, muggy air draped across the nation’s midsection, strong to severe thunderstorms will develop over the northern tier of the country. Severe thunderstorms will be possible over South Dakota, northern Nebraska, northwest Iowa and southwest Minnesota. These thunderstorms will be capable of producing large hail, dangerous straight line winds and isolated tornadoes. In addition, heavy rain associated with these thunderstorms will bring a threat of flash flooding to southeast North Dakota, eastern South Dakota and southeast Minnesota. Scattered showers and thunderstorms will also be possible over the central Plains.

Meanwhile, a separate area of low pressure will trek eastward over the Great Lakes. This system will usher numerous area of thunderstorms over the Great Lakes, the Ohio Valley, the Tennessee Valley and the Mid-Atlantic. An onshore flow from the Gulf of Mexico will trigger thunderstorm activity across the Gulf Coast and the Southeast. High pressure will keep conditions clear across the Northeast.

Out west, monsoonal moisture will surge across the Intermountain West and the Desert Southwest. Isolated showers and thunderstorms will be possible across a handful of states, while the West Coast will avoid wet weather on Wednesday.

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