Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 458 AM EDT Thu May 21 2020 Valid 12Z Thu May 21 2020 - 12Z Sat May 23 2020 ...There is a moderate risk of excessive rainfall over the Central/Southern Appalachians, heavy rain to drench the southern Mid-Atlantic... ...Daily episodes of severe weather to transpire in the High Plains, critical fire weather conditions linger across portions of the Southwest and Four Corners Region... ...Showers, mountain snow, and below normal temperatures in the Northwest... A slow moving upper-level low over the Ohio Valley travels to the Mid-Atlantic bringing heavy rain over the Central/Southern Appalachians and Mid-Atlantic. Rainfall rates will become excessive within bands of embedded thunderstorms. The storm's seemingly endless supply of moisture, its slow movement, and the region's overly saturated soil are a recipe for significant flooding on Thursday. Flash Flood Watches remain in effect for parts of the Eastern Ohio Valley, Southwest Virginia, and much of the Carolinas. Moderate risks for excessive rainfall are forecast for the Central/Southern Appalachians of Southwest Virginia on Thursday where widespread flooding is likely. Landslides and debris flows are possible within steeper terrain. A few severe storms are possible along the coastal Carolinas and into Southern Georgia this evening and into Thursday. In addition, brisk onshore winds responsible for coastal flooding in the Virginia Tidewater, the lower DelMarVa Peninsula, and North Carolina Outer Banks. In the Heartland, rounds of severe storms are expected to develop up and down the Great Plains this evening and through Saturday. This is due to the combination of a slow progressing frontal boundary to the north and the dry line to the south acting as triggers for thunderstorms up and down the High Plains this evening and again on Thursday. The front's slow progression could also lead to flash flooding concerns in areas impacted by heavy thunderstorms. To the south, dry and windy conditions will prevail across the Southwest, promoting elevated to critical fire weather conditions across much of the Southwest through through Friday. In the West, an upper level trough is swinging through the Northern Rockies this with scattered heavy showers and thunderstorms dotting parts of the Northwest. As this upper low heads north into the Canadian Prairies, another upper low will track into the Pacific Northwest on Thursday. This next storm system will be responsible for ushering in considerably cooler temperatures, numerous showers, and even some mountain snow for both Thursday and Friday. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php