Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 349 AM EDT Wed Aug 19 2015 Valid 12Z Wed Aug 19 2015 - 12Z Fri Aug 21 2015 ...There is a slight risk of severe thunderstorms over parts of the Great Lakes... ...Temperatures will be 10 to 20 degrees below average over parts of the Upper/Middle Mississippi Valley and Southern Plains... A slow moving front extending from the Upper Great Lakes to the Middle Mississippi Valley then to the Southern Plains will move eastward to the Lower Great Lakes/Central Appalachians then to the Western Gulf Coast by Thursday. The associated surface low over the Upper Mississippi Valley will move northward into East-Central Canada by Thursday morning. The system will produce rain over the Upper Great Lakes/Upper Mississippi Valley on Wednesday that will, likewise, move into Canada by late Wednesday night. Showers and thunderstorms will develop along and ahead of the front from the Great Lakes to the Middle Mississippi Valley/Southern Plains that will march eastward to the Northern/Central Appalachians to the Southeast/Gulf Coast by Thursday evening. In addition, moisture streaming out ahead of the boundary will aid in producing showers and thunderstorms over parts of the Southeast to the Mid-Atlantic on Wednesday into Thursday morning. Additionally, weak monsoonal moisture and diurnal heating will aid in producing showers and thunderstorms over parts of the Southern High Plains/Southern Rockies during the afternoon and evening hours on Wednesday and Thursday. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php