Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 355 PM EDT Sun Aug 20 2017 Valid 00Z Mon Aug 21 2017 - 00Z Wed Aug 23 2017 ...Flash flooding and severe thunderstorms will be possible over portions of the Upper Mississippi Valley Sunday evening into Monday... ...The threat for locally heavy rainfall across the Southern Rockies will continue into Monday... A cold front pressing out of the north central U.S. early this week will serve as focus for showers and thunderstorms while it stalls over portions of Upper Mississippi Valley Sunday evening into Monday. An abundance of moisture and instability along the lingering boundary should heighten the risk for flash flooding and severe weather within developing convection, especially from eastern Nebraska into Iowa and northern Missouri. Monday night into Tuesday, an amplifying upper trough should help push the front south and eastward, shifting the focus for heavy rain and thunderstorms into the Upper Great Lakes and Middle Mississippi Valley. The combination of monsoonal moisture and impulses of energy aloft will keep heavy rainfall a threat over the Southern Rockies, with the locations across New Mexico and extreme West Texas expected to see the greatest threat for any flash flooding or local runoff concerns. Farther west, a relatively stagnant upper low centered off California coast should help foster mainly scattered to isolated shower activity across portions of California and the Central Great Basin early this week. Gerhardt Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php