Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 345 AM EDT Thu Aug 19 2021 Valid 12Z Thu Aug 19 2021 - 12Z Sat Aug 21 2021 ...Heavy rain and possible flash flooding lingers today in the East as Post-Tropical Cyclone Fred moves offshore... ...Severe thunderstorms and flash flooding are possible as a potent cold front moves through the north-central U.S. and the Intermountain West... Post-Tropical Cyclone Fred is currently moving into the northeastern U.S., and will continue to track northeastward across New England today and tonight before shifting offshore on Friday. Tropical moisture with Fred will continue to cause heavy rain today along its track. A Slight Risk of excessive rainfall and Flash Flood Watches are in effect today into tonight for the Northeast, as heavy downpours could cause scattered flash floods there. Additional showers and thunderstorms are also likely farther south across the Lower Mississippi, Tennessee, and Ohio Valleys into the Mid-Atlantic region over the next couple of days with the moist environment. While storms are not likely to be severe in these areas, isolated flash flooding is possible. More rain today across eastern Kentucky, southwestern Virginia, and southern West Virginia could be particularly problematic, as that area has seen ample rainfall due to Fred's passage over the last couple of days, so there is a Slight Risk of excessive rainfall in place there. More focused rainfall along a front/trough in the eastern Mid-Atlantic tomorrow could create scattered flash flooding issues as well. A strong upper-level trough/low (for August) will continue moving through the Intermountain West today and into central/northern portions of the High Plains on Friday. This feature is forecast to push a potent cold front across these regions, leading to cooler than average temperatures in the western third of the CONUS. High temperatures in particular should be 10 to 20 degrees below normal for the Central Great Basin into the Northern Rockies and Northern High Plains, while ahead of the front, highs will be in the 90s for portions of the Dakotas into Minnesota today. Additionally, the weather pattern and monsoonal moisture inflow will provide support for widespread rain and thunderstorms in portions of the western and central U.S., some of which could be severe. The Central High Plains in particular could see severe weather today and tonight, with a Slight Risk of severe weather in place and tornadoes, wind, and hail all possible. Meanwhile, the better chance for flash flooding today is expected for southwestern Utah into western Colorado today where the Slight Risk of excessive rainfall is delineated, but a Marginal Risk for isolated flash floods stretches north and eastward as well. For Friday, the surface low pressure system deepening in the Northern Plains should lead to a threat for severe storms and flash flooding once again. Slight Risks of both severe weather and flash flooding are in place for portions of the Northern Plains and Upper Midwest. Additionally, given the deep upper-level low, the highest elevations of the West could even see light snow with the precipitation. Unfortunately, poor air quality persists in portions of the West despite the cooldown, and an Elevated Risk of fire weather and Red Flag Warnings are in effect today for portions of northern California. Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php