Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 338 PM EDT Thu May 12 2016 Valid 00Z Fri May 13 2016 - 00Z Sun May 15 2016 ...Flash flooding possible across portions of the Ohio and Tennessee valleys and central Appalachians... ...Below average temperatures on the way for much of the central and eastern U.S... A cold front will bring showers and thunderstorms to areas from the Great Lakes and Northeast to the Gulf Coast tonight and Friday. Heavy rainfall may produce flash flooding for some areas of the Ohio and Tennessee valleys as well as portions of the central Appalachians through tonight. On Friday, the most widespread shower and thunderstorm activity will be along across the Mid-Atlantic and Northeast. A secondary cold front will quickly follow in the wake of the first one, bringing rain and snow showers to portions of the northern plains tonight, and then another round of showers and thunderstorms to the Mid-Mississippi and Ohio valleys as well as the Mid-Atlantic and Northeast later Friday into Saturday. Showers and thunderstorms associated with this front will also affect the southern plains on Saturday. This secondary cold front will be the leading edge of a much cooler air mass. Behind this front, high temperatures will be 10 to 20 degrees below average across the northern plains and Upper Midwest on Friday. These cooler temperatures will spread into the southern plains and Ohio valley by Saturday. Across the West, generally dry conditions will prevail through Friday, but showers and thunderstorms will become more common on Saturday as an upper-level low moves in from the Pacific and interacts with a stationary frontal boundary across the northern Intermountain region. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php