Weather Underground Forecast for Wednesday, September 21, 2011.
The storm system in the Upper Midwest will slowly weaken and lift northeast Wednesday, carrying a cold front through Mississippi and Ohio valleys. Expect light to moderate rain to spread from the Upper Midwest to the Great Lakes, with chances for showers and thunderstorms along and ahead of the cold front. In addition to the precipitation, much cooler air will move into portions of the Northern Plains and Upper Midwest Wednesday. Highs are expected only in the upper 40s and 50s.
Moving to the East, a weakening frontal boundary from the Northeast into the Southern Plains will continue to bring a threat for showers and thunderstorms to the region. In addition, as the cold front from the Ohio and Tennessee Valley approaches, it will also have an effect on enhancing shower and thunderstorm activity Wednesday afternoon.
Out West, a Pacific cold front is expected to drop southeast into northwestern Washington Wednesday night and Thursday morning, dumping light to moderate rain. Otherwise, a strong ridge of high pressure will continue to dominate across the Western U.S., bringing hot and sunny weather. The immediate coastal region will remain seasonal, with areas of morning and night low clouds and fog over Southern California. Temperatures in the Lower 48 states Tuesday have ranged from a morning low of 26 degrees at Stanley, Idaho to a high of 104 degrees at Thermal, Calif.