Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 354 AM EDT Tue May 18 2021 Valid 12Z Tue May 18 2021 - 12Z Thu May 20 2021 ...There is a Moderate Risk of excessive rainfall over the Central Gulf Coast to the Southern Plains through Thursday... ...There is a Slight Risk of severe thunderstorms over the Southern Plains through Wednesday morning... The quasi-stationary front extending from the Middle Mississippi/Western Ohio Valleys to the Southern Plains will slowly dissipate by Wednesday night. The dryline oscillation over the Southern Plains will also dissipate ahead of the next system. Showers and thunderstorms will continue to develop in the moist air over the Southern/Central Plains and the Middle/Lower Mississippi Valley through Thursday morning. The WPC has issued a Moderate Risk of excessive rainfall over the Central Gulf Coast to the Southern Plains through Thursday. The showers and thunderstorms will produce heavy rain over the region producing numerous areas of flash flooding. Additionally, the heavy rain may cause many streams and possibly larger rivers to flood. On Wednesday into Thursday morning, the Moderate Risk is mainly over the Southern Plains. Additionally, rain will develop over parts of the Upper Midwest on Tuesday into Wednesday. Meanwhile, a front extending from the Northern Rockies to Northern California will advance eastward to the Upper Midwest westward to the Great Basin by Thursday morning. Rain and highest elevation snow will develop over parts of the Pacific Northwest into parts of the Northern Rockies on Tuesday, ending on Wednesday morning. Behind the front, the snow levels will lower as the rain and higher elevation snow returns to the Pacific Northwest/Northern Rockies later on Wednesday afternoon into Thursday morning. As the front moves onto the Northern High Plains, showers and thunderstorms will develop overnight on Tuesday, moving into the Northern Plains by Wednesday morning. On Wednesday, showers and thunderstorms will develop over parts of the Upper Mississippi Valley/Upper Great Lakes through Thursday morning. Elsewhere, upper-level energy will produce rain over parts of Northern New England through Tuesday evening. Easterly flow off the Atlantic will aid in producing rain with embedded thunderstorms over the east coast of Florida through Thursday morning. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php