Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 PM EDT Thu Apr 18 2019 Valid 00Z Fri Apr 19 2019 - 00Z Sun Apr 21 2019 ...Severe thunderstorms and flash flooding expected for the Lower Mississippi and Tennessee Valleys through Thursday night, shifting to the Eastern Seaboard on Friday as a strong cold front moves east... ...Precipitation chances will increase in the Northwest as a cold front moves through... An upper-level trough/low that is particularly deep for this time of year will move from the Plains into the Mississippi Valley and into the Ohio Valley over the next couple of days. This trough will drive a cold front through the central and eastern U.S., and widespread rain and thunderstorms are expected along and ahead of it as a plume of moist air from the Gulf of Mexico streams in. Through Thursday night, a Moderate Risk of excessive rainfall/flash flooding is in place for portions of the Lower Mississippi and the Tennessee Valley as heavy rain is expected to continue. In terms of severe weather, an Enhanced Risk of severe thunderstorms is in effect from the Storm Prediction Center for these areas and for the Central Gulf Coast. High winds and tornadoes are both possible in these areas. On Friday and Friday night, the severe and flash flood threats will shift eastward with the cold front. An Enhanced Risk of severe weather is in place for the southern Mid-Atlantic and Southeast, and the Mid-Atlantic region and parts of the Northeast will have a Slight Risk of flash flooding in effect. Heavy rain will remain a possibility in the Northeast on Saturday. A cold front is forecast to move southeastward through the Pacific Northwest Thursday night, the Northern Great Basin on Friday, and into the Northern Rockies and Central Great Basin on Saturday. Light to moderate precipitation will spread across these areas with the front. While the highest elevations could see snow, heavy snow is not expected through Saturday. Rainfall totals are forecast to be a half inch to an inch in lower elevations. Temperature-wise, record high minimum temperatures are expected to be widespread on Friday morning across the Eastern Seaboard ahead of the approaching cold front, and again on Saturday morning in the Mid-Atlantic and Northeast. Behind the cold front on the other hand, high temperatures of 10 to 20 degrees below average are forecast for the Ohio and Tennessee Valleys on Friday, spreading into the Southern Appalachians on Saturday. The West will see much above average temperatures on Friday, with record high minimum temperatures likely there as well, and warm temperatures should spread into the Plains on Saturday. The cold front coming through the northwestern U.S. is expected to cool high temperatures down to a few degrees below average there on Saturday. Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php