Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Sun Aug 20 2017 Valid 12Z Sun Aug 20 2017 - 12Z Tue Aug 22 2017 ...Heavy rain and flash flooding possible over parts of the Southwest and parts of the Rockies this weekend... ...Heavy rainfall possible along a frontal boundary in the Upper Midwest on Sunday and into Monday... ...Afternoon showers and thunderstorms may linger into Monday across the Southeast and Gulf Coast states... The monsoon will pick up again across the Southwest and southern Rockies into early next week. A surge of moisture into the region will spark afternoon showers and thunderstorms with a focus on southern New Mexico and southeast Arizona on Sunday. Thunderstorm activity could be more widespread across the Southwest on Monday, but the greatest potential for heavy rainfall will be across central New Mexico. Flash flooding will be a concern across southern New Mexico and extreme southwest Texas on Sunday. The flash flood threat will expand on Monday with a another day of heavy rainfall expected across the region. A frontal boundary moving across the northern and central plains will become stalled while the northern portion stretches across the Great Lakes. This boundary will provide a focus for shower and thunderstorm activity into early next week. Scattered showers and thunderstorms are expected ahead of the cold front as it pushes across the central plains and upper Midwest on Sunday. The stalling boundary will allow moisture to pool along the front by Monday, increasing the rainfall potential both in coverage and intensity. More widespread thunderstorms are expected on Monday, with the potential for flash flooding across parts of the upper Midwest. South to southeasterly winds off the Gulf of Mexico carrying rich tropical moisture will spark afternoon thunderstorms across the Southeast into Monday. These thunderstorms will produce locally heavy rainfall but should remain more scattered in nature. Krekeler Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php