Weather Underground Forecast for Wednesday, April 18, 2012. In the Deep South, the front will slowly move east from the lower Mississippi Valley to the Southeast and Mid-Atlantic Wednesday. Showers and thunderstorms will continue to fire up along this frontal boundary. In particular, from northeastern Florida Peninsula into southern and eastern South Carolina can expect the heaviest rain. Some storms maybe severe, capable of producing damaging winds mainly in the afternoon. The precipitation amount in the Mid-Atlantic will be light so it is not going to help too much with the rainfall shortage. Moving northward, a low pressure system is expected to push into the Upper Midwest Wednesday morning, producing widely scattered showers and thunderstorms. Heavier precipitation is anticipated ahead of the cold front. This system will move through the Great Lakes Wednesday evening and then into Quebec Thursday. Out West, a Pacific front will be approaching the coast Wednesday morning, bringing light to moderate rain with mountain snow to the Pacific Northwest and far northwestern California. This system is expected to weaken as it moves ashore. Meanwhile, a weak front will remain over the Northern Rockies, keeping scattered snow showers with lower elevation rain going. Temperatures in the Lower 48 states Tuesday have ranged from a morning low of 3 degrees at Grand Marais Airport, Minn. to a high of 90 degrees at Palm Springs, Calif.