Portola Valley, CA

Weather Underground Forecast for Wednesday, May 22, 2013.

After an active severe weather pattern during the beginning of the week, cooler and relatively calmer weather conditions will return to much of the Central U.S. on Wednesday as the trough of low pressure impacting the region moves to the East. As the trough progresses, an associated low pressure system will reorganize near southern Lake Michigan and will continue northeastward across Michigan toward the Lower Great Lakes through Wednesday evening. Expect rain showers to continue across the Upper Midwest into areas of the inland Northeast throughout this transition. Meanwhile, the system's associated cold front will trail southwestward from the low across the Ohio and Tennessee Valleys through the Lower Mississippi Valley and into the Southern Plains. Favorable energy and environmental conditions ahead of the cold front combined with ample moisture from the Gulf of Mexico will set the stage for shower and thunderstorm activity through the day. Areas just east of the advancing cold front will experience the heaviest amounts of precipitation, with areas of flooding and flash flooding possible in parts of eastern Texas and Louisiana. As the cold front continues eastward, areas of the Lower Great Lakes into the Ohio and Tennessee Valleys are at slight risk of severe thunderstorm development through the evening. Severe storms in these regions may become capable of producing damaging wind gusts, marginally severe hail, and even a few tornadoes during the evening hours.

Elsewhere, scattered showers and thunderstorms will remain possible along the East Coast and in the Florida Peninsula. Out West, a cold trough of low pressure will become anchored over the Pacific Northwest, bringing cool, below normal temperatures to the Pacific Northwest and California, as well as scattered precipitation to the Northwest.