Weather Underground Forecast for Monday, September 12, 2011.
Wet and cooler weather will develop over the Midwest and East during the next couple of days as a developing low and cold front drop in from the Canada and a trough of low pressure moves through the eastern third of the nation. Showers and thunderstorms will develop ahead of this cold front in northern Wisconsin and Michigan. Some of these storms will have the possibility of turning severe during the afternoon. The main concern with these storms are damaging wind gusts, large hail, perhaps a tornado. Meanwhile, a cooler airmass from the north will accompany this system as it moves across the Midwest during the beginning of the week. This will lead to significantly cooler daytime highs in the Plains and the Great Lakes by the mid-week. To the east, showers and thunderstorms will linger in parts of the Ohio and Tennessee Valleys through the Mid-Atlantic. To the south, moist flow across the Florida Peninsula will maintain areas of showers in south Florida.
In the West, low pressure will continue to create chances of showers and slow moving thunderstorms in the California valleys and Sierra Nevadas. Additional showers and thunderstorms are expected in the Southwest and the Central and Southern Rockies as monsoonal moisture spreads across the Four Corners. Temperatures in the Lower 48 states Sunday have ranged from a morning low of 30 degrees at West Yellowstone, Mont. to a high of 100 degrees at Austin, Texas.