Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 422 PM EDT Thu Aug 19 2021 Valid 00Z Fri Aug 20 2021 - 00Z Sun Aug 22 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 will continue a northeastward march into New England through tomorrow before exiting offshore by Saturday. Tropical moisture associated with Fred will produce showers and thunderstorms along the way in northern New England, where a Slight Risk of excessive rainfall is in effect through tonight. Isolated severe weather is also possible over eastern New England today (including the Boston Metro) where isolated tornadoes and severe wind gusts are possible. Additional thunderstorm activity atop areas that have recently received ample rain could cause isolated to scattered flash floods from the Mid-Atlantic and further southwest into the Southern Plains through the weekend. Eastern Kentucky, southwestern Virginia, and southern West Virginia could be particularly problematic today given Fred's recent passage, 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. No severe weather is anticipated with this activity. 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 upper-level feature is forecast to push a potent cold front across these regions, leading to much 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 for tornadoes, wind, and hail. Thunderstorm development is already underway over the region, and a Severe Thunderstorm Watch extends over the region through tonight. The heavy rain threat should focus further west today in western Colorado and eastern Utah, as the aforementioned upper-level trough interacts with the moist, unstable airmass in place and thunderstorms train over the same location. Accordingly, Flash Flood Watches are in effect for the area through this evening. The severe weather and heavy rain threat will shift into the Northern Plains/Upper Midwest to begin the weekend as the frontal system migrates east through tomorrow. Slight Risks of both severe weather and flash flooding are in place for portions of the Northern Plains and Upper Midwest for Friday. After the frontal passage, cool temperatures can be expected in the Northern Plains tomorrow, with below average highs in the mid-70's likely before temperatures moderate to around normal beginning Sunday. Moreover, the highest elevations of the West could even see light snow with the precipitation given the strong upper-low in place. Otherwise, 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. Asherman/Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php