Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 342 AM EDT Tue Aug 18 2015 Valid 12Z Tue Aug 18 2015 - 12Z Thu Aug 20 2015 ...There is a slight risk of severe thunderstorms over parts of the Southern/Central Plains into parts of the Middle Mississippi Valley... ...Heavy rain possible for parts of the Middle Missouri Valley into parts of the Upper Great Lakes and the Tennessee Valley... ...Temperatures will be 10 to 25 degrees below average over parts of the Central/Northern Plains... A wave of low pressure over the Central Plains will move northward to the Upper Great Lakes by Wednesday evening. The associated front will move eastward from the Central Plains to the Great Lakes southwestward to the Tennessee Valley then roughly westward to the Southern Plains by Wednesday. Showers and thunderstorms will develop along and ahead of the boundary from parts of the Northeast to the Central/Southern Plains will likewise advance eastward to the Great Lakes/Tennessee Valley/Southern Plains by Wednesday evening. In addition, moisture moving northward from the Gulf of Mexico over the Central Gulf Coast to the Southeast and northward to Southern Ohio Valley/Central Appalachians will aid in producing showers and thunderstorms over the region on Tuesday. By late Tuesday, the moisture will move into parts of the Mid-Atlantic triggering showers and thunderstorms over parts of the Mid-Atlantic into parts of the Southeast and the Ohio Valley through Wednesday evening. Upper-level energy moving southeastward out of Western Canada will advance to the Upper Mississippi Valley by Wednesday. The energy will trigger rain over parts of the Northern High Plains and Northern Plains that will lift into the Upper Mississippi Valley/Upper Great Lakes by Wednesday evening. Rain will also develop over parts of the Central High Plains on Tuesday night into Wednesday morning. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php