Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EDT Fri Aug 18 2017 Valid 00Z Sat Aug 19 2017 - 00Z Mon Aug 21 2017 ...Slight risks of severe thunderstorms and flash flooding for the portions of the Midwest and Mid-Atlantic on Friday afternoon and evening... ...Heavy rain and flash flooding possible over parts of the Southwest this weekend... ...Slight risks of severe thunderstorms and flash flooding for portions of the Northern Plains/Upper Mississippi Valley... A surface low pressure system will continue to pass through the Ohio Valley, Mid-Atlantic and Northeast regions this weekend which will generate scattered to widespread showers and thunderstorms. Some of these storms will be well organized, potentially becoming severe and producing periods of heavy rain. The Storm Prediction Center has identified portions of Missouri, Minnesota and the Mid-Atlantic as having a a slight risk for severe thunderstorms through late tonight. Showers and thunderstorms will persist from the Southeast to the Mid-Atlantic as the trailing end of the front stalls over the region. An upper-level low will move over the southwest U.S. this weekend. Ample moisture streaming into the Southern Plains and Southwest will trigger widespread convection as it interacts with stationary boundary then lifts as a warm front into the Southern/Central Plains. Much of the Mongolian Rim, Southern and Central Rockies and the surrounding valleys will have an increased risk for heavy rainfall and flash flooding this weekend. Areal averages of 1 to 2 inches are forecast for much of New Mexico over the next few days - localized amount near 3 inches may be possible. A cold front will pass through the Intermountain West through Saturday morning before tracking across the Northern High Plains and Upper Midwest Sunday into Monday. Additional showers and thunderstorms will spread across the northern tier states this weekend. Heavy rain and flash flooding will be possible Sunday afternoon and evening for portions of southern Minnesota and northern Iowa. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php