Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Mon Aug 20 2018 Valid 00Z Tue Aug 21 2018 - 00Z Thu Aug 23 2018 ...Heavy rain and severe weather expected across the Mississippi Valley through tonight ... ...Active weather returns for the East Coast for the coming days... ...Fire weather and air quality concerns continue for portions of the Western U.S... A very strong low pressure system will continue to lift across the Mid and Upper Mississippi Valley this evening, reaching the Ohio Valley and Lower Great Lakes by overnight. From this will stretch a robust cold front which will drape southward into the Southern plains. Ahead of the frontal system, warm and moist air will be transported from the Gulf of Mexico spawning widespread showers and thunderstorms across much of the eastern U.S. and Southeast. The heaviest rainfall and best thunderstorm potential will be located along the frontal boundary and close to the center of low pressure. The Storm Prediction Center has outlined a portion of the Mid/Lower Mississippi River as being in an enhanced risk of severe thunderstorms through tonight. A slight risk of severe weather is also in effect for the surrounding areas. A Severe Thunderstorm Watch is in effect for northeast Arkansas, Southeast Missouri, and southern Illinois. The Weather Prediction Center has also outlined a large slight risk area for excessive rainfall stretching from the Lower Mississippi River northward to Lake Michigan and westward into Iowa through tonight. Flooding is ongoing along the Missouri River in Nebraska and Iowa, and flash flood watches have been issued across southern Wisconsin and a portion of southern Virginia and north-central North Carolina. As this system continues to progress eastward over the coming days, so to will the severe weather and flash flooding threats. Meanwhile, behind this system, a large area of high pressure will set in across the eastern U.S., resulting in much drier weather to finish out the work week. Fire weather risks will continue to be elevated across the West, especially for the Pacific Northwest, Intermountain West, Great Basin, and portions of the Northern Rockies through Tuesday. Red flag warnings are in effect for parts of these regions due to high winds and low relative humidities. Air quality also remains a concern due to the smoke from ongoing fires. Air Quality Alerts remain in effect for all of Washington, Oregon, northern Idaho, and western Montana. Furthermore, fires burning in British Columbia, Canada are transporting smoke southward into portions of Minnesota, where an Air Quality Alert is also in effect. Monsoonal moisture will surge back into the Southwest by Tuesday and expand across the Great Basin and Southern/Central Rockies, resulting in scattered to widespread showers and thunderstorms through the day. These storms will then shift eastward to encompass a portion of the Central and Southern Plains by mid week. The best shower and thunderstorm potential will be in the afternoon and early evening each day. Some of these storms could produce flash flooding, especially in favorable terrain and urban areas, as well as across burn scar regions. Flash flooding will also be a concern in the high plains, where above normal rainfall has already occurred over the past week. Wix Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php