Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Wed Aug 18 2021 Valid 12Z Wed Aug 18 2021 - 12Z Fri Aug 20 2021 ...Fred will bring a Moderate Risk of flash flooding as well as a Slight Risk of severe weather to parts of the East today... ...Much cooler and wetter conditions are forecast for the West over the next couple of days... Tropical Storm Fred is forecast to transition to a post-tropical cyclone today as it moves northward across the Central Appalachians. Tropical moisture associated with the system will continue making its way into the eastern U.S., causing continued rain and thunderstorms. Today into tonight, the heaviest rainfall and the greatest chance of flash flooding (a Moderate Risk of excessive rainfall) are expected over portions of northern Pennsylvania and southern New York. Meanwhile a Slight Risk of excessive rainfall expands southward across much of the Mid-Atlantic region and then across portions of the eastern Carolinas that have received quite a bit of rainfall recently. Thus scattered to numerous flash floods are likely for these portions of the Eastern Seaboard, and Flash Flood Watches are in effect. Another threat today associated with Fred will be severe weather. There is a Slight Risk of severe thunderstorms across parts of the Mid-Atlantic today, with some tornadoes possible as well as gusty winds. In the West, a potent cold front pushed by an upper-level low will continue slowly moving through the Northern High Plains back into the Central Great Basin through tonight, likely pushing past the Central Rockies later on Thursday. The energy provided by this system as monsoonal moisture streams into 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 parts of the Four Corners states and into Wyoming today, and a Marginal Risk could stretch into the Northern Plains by Wednesday. There is also potential for severe weather in the Central High Plains on Thursday for wind and hail threats. Given the strong cold front, much below normal temperatures especially in terms of highs are expected, particularly today in Montana, where highs could be as much as 30 degrees below average. 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. Unfortunately, poor air quality persists in portions of the West despite the cooldown. In the center of the country, hot temperatures in the 90s and nearing 100F in some areas are again expected for the Northern Plains and Upper Midwest ahead of the cold front. Scattered showers and thunderstorms are forecast across the Southern Plains into the Lower Mississippi and Tennessee Valleys, and Marginal Risks of excessive rainfall in place. Below normal high temperatures generally in the 80s to low 90s can be expected there. Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php