Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 402 PM EDT Sat Aug 19 2017 Valid 00Z Sun Aug 20 2017 - 00Z 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... An upper level low across the Southwest U.S. is expected to move very slowly eastward through the rest of the weekend and into early next week. This will continue to trigger diurnally driven showers and thunderstorms the next several days from the Four Corners region into the Central Rockies, as well as back into the higher terrain of the central Intermountain West and California. Heavy rainfall will be possible and WPC has highlighted portions of these areas in a marginal to slight risk for flash flooding. Please refer to the Excessive Rainfall Outlooks issued by WPC for additional details. A cold front moving across the Upper Mississippi Valley and southward through the central Plains tomorrow will allow for the development of showers and thunderstorms along the boundary on Sunday, moving into the Upper Midwest and Great Lakes on Monday. Strong to locally severe thunderstorms and moderate to heavy rainfall will be possible, particularly across portions of the Upper Midwest Sunday and into Monday as the surface front slows and eventually stalls across this region. WPC has highlighted an area across Iowa and into northern Missouri with a slight risk for flash flooding both Sunday and Monday. Afternoon high temperatures behind the front across the Northern Plains should cool to near or slightly below normal for this time of the year. Elsewhere, the tail end of a boundary exiting the Northeast should linger across portions of the Southeast Sunday into Monday keeping showers and thunderstorms in the forecast from the Southeastern states to the Gulf Coast. Across the Northeast and the Northwestern states, surface high pressure should dominate much of the short range period which will allow for mostly clear skies, comfortable temperatures, and little to no rainfall. Santorelli Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php