Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 426 PM EDT Wed Aug 18 2021 Valid 00Z Thu Aug 19 2021 - 00Z Sat Aug 21 2021 ...Additional flash flooding and severe weather anticipated in the Northeast/Mid-Atlantic associated with Post-Tropical Cyclone Fred.. ...Much cooler and wetter conditions are forecast for the West/Northern Plains over the next couple of days... Fred has finally transitioned to a post-tropical cyclone this morning as it tracks into the Northeast today, shifting the threat of heavy rainfall and severe weather into the Northeast and Mid-Atlantic through Friday. The greatest threat of heavy rain and excessive rain today remains focused over the Moderate Risk area in North Pennsylvania and South-Central New York, where numerous instances of flash flooding can be expected as repeated rounds of thunderstorms fall over the same area. Outside of the Moderate Risk, scattered flash flooding is anticipated over a broad area including much of the Mid-Atlantic and eastern Carolinas given the antecedent heavy rainfall in the region. The same thunderstorms responsible for heavy rain may also produce severe weather today, reflected by a Slight Risk of severe storms across the Northeast and Mid-Atlantic today for a few tornadoes and some gusty winds. By tomorrow, lingering hazardous weather associated with remnants of Fred will migrate into New England, where scattered flash floods and isolated tornadoes are possible with thunderstorm activity over the area. What is left of Fred should exit northern New England on Saturday, leaving scattered thunderstorms and isolated flash flood chances in its wake from the Northeast toward the Tennessee as a front/trough lingers around. In the West, a potent cold front pushed by an upper-level low will meander through the Northern High Plains back into the southern Great Basin through tonight, likely pushing past the Central Rockies later on Thursday. The interaction with the front and associated upper low with monsoonal moisture pooling over the West will lead to showers and thunderstorms across much of the interior regions. Marginal to Slight Risks of excessive rainfall are in place across central parts of the Four Corners states to the Wyoming/Colorado border, and a Marginal Risk extends just north of the Four Corners into the Rockies and Northern Plains tomorrow. Some severe storms capable of producing strong wind gusts are also possible today over Central Utah, before the severe threat shifts to the Central High Plains on Thursday for wind and hail threats. The strong front will provide some much needed relief from the recent brutal heat in parts of the West; high temperatures pushing 30 degrees below average are possible today, particularly today in Montana. Milder than normal temperatures also stretch into the Great Basin and toward the Southwest today, with the Central Rockies seeing cooler temperatures on Thursday as the cold front pushes eastward. The very cool temperatures will moderate slightly going into the weekend, but will generally remain at or below average through the short-range forecast period. Unfortunately, poor air quality persists in portions of the West despite the cooldown. Ahead of the cold front in the Central U.S., hot temperatures in the 90s and nearing 100F in some areas are again expected for the Northern Plains and Upper Midwest. Moreover, shower and thunderstorms ahead of the front could produce some flash flooding on Friday in the Northern Plains where a Slight Risk of excessive rain is in effect. Below average high temperatures can be expected in the Northern Plains on Saturday behind the front. Asherman/Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php