Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 343 PM EDT Tue Aug 11 2015 Valid 00Z Wed Aug 12 2015 - 00Z Fri Aug 14 2015 ...Heavy rain and flash flooding possible for portions of the southwestern U.S... ...Showers and thunderstorms expected for much of the East Coast tonight... ...Above average temperatures expected from the Pacific Northwest to the northern plains... A moist and unstable air mass will remain in place across the southwestern U.S. through next couple days as southern persists along the western periphery of the ridge of high pressure centered over the southern plains. As a result, scattered showers and thunderstorms are expected, with the greatest concentration occurring during the afternoon and evening hours in areas of terrain. Deep moisture in atmosphere will allow for the possibility of locally heavy rainfall -- and WPC is forecasting a slight risk of flash flooding through tonight across portions of the Four Corners region. A cold front will move across the eastern U.S. late today into tonight, bringing scattered showers and thunderstorms to much of the eastern U.S. The most widespread area of rain and thunderstorms is expected to occur across New England tonight along and north of a surface warm front. Additional areas of widespread showers and thunderstorms are possible across coastal portions of the Mid-Atlantic region tonight before moving offshore. The frontal boundary will move off the East Coast on Wednesday with a few scattered showers and thunderstorms lingering across the Northeast. Cooler air will move into much of the East behind the front, with afternoon high temperatures expected to be 5 to 10 degrees below average. The frontal boundary will slow its forward speed along the Gulf Coast and become nearly stationary at times, keeping a possibility of showers and thunderstorms in place into Thursday. Temperatures are expected to be above average through the next couple days from the Pacific Northwest to the northern plains as high pressure at the mid and upper-levels will cause the air mass to sink and warm. Afternoon high temperatures will be 10 to 15 degrees above average in many areas. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php