Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 444 AM EDT Wed Aug 28 2013 Valid 12Z Wed Aug 28 2013 - 12Z Fri Aug 30 2013 ...Excessive heat continues across the north central U.S.... ...Flash flooding possible today and tonight across portions of the northern Plains and eastern Ohio River valley/central Appalachians... A large upper-level ridge of high pressure will drift slowly westward across the central U.S. through the short range forecast period. This ridge will keep the hot conditions in place for areas of the north central U.S. through today. The possibility will exist for some relief from the heat in the form of showers and thunderstorms. A slow-moving east to west oriented frontal boundary across the Midwest will act as a focus for shower and thunderstorm development today into tonight across the northern Plains. There is a slight risk of excessive rainfall/flash flooding across portions of the northern Plains, especially if an organized area of showers and thunderstorms develops. The same frontal boundary extends eastward across the Ohio River valley into the Mid-Atlantic states. Showers and thunderstorms are ongoing this morning across these areas. There is a slight risk of excessive rainfall/flash flooding today across portions of the eastern Ohio River valley and central Appalachians as these showers and thunderstorms pass through. Shower and thunderstorm activity will shift southward and eastward through today as the front pushes southward. Widespread showers and thunderstorms will reach the Outer Banks by early Thursday and move offshore from there. However, isolated to scattered showers and thunderstorms will remain possible across the southeastern states. Across the West, scattered showers and thunderstorms, mainly during the afternoon and evening, will continue each day as a relatively moist air mass originating in the tropics remains in place. A stationary frontal boundary across the Intermountain West may serve to enhance shower and thunderstorm activity. Finally, a frontal system from the Pacific will approach the northwestern states by Thursday, spreading deeper moisture and the potential for showers and a few thunderstorms into the Pacific Northwest. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php