Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 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 today... ...Active weather returns for the East Coast this week... ...Air quality remains a concern for parts of the Western U.S... A very strong low pressure system will continue to lift across the Mid and Upper Misssipi Valley this evening, reaching the Ohio Valley and Lower Great Lakes by overnight. From this will stretch a robust cold front which will drape soutward 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 perssure. 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 Missippi River northward to Lake Michigan and westward into Iowa through tonight. As this system continues to progress eastward over the coming days, so to will the severe weather and excessive rainfall/flash flooding threats. Meanwhile a strong area of high pressure will move into much of the United States behind this frontal feature. Fire weather risks continue to be elevated across the western U.S., 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 areas due to high winds and low relative humidities. Air quality also remains a concern due to the smoke from ongoing fires. Air Quality Alerts continue to be 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. Late afternoon and early evening thunderstorms will return across the Southwest and Great Basin on Tuesday and Wednesday. Some of these storms could produce flash flooding especially in favorable terrain and urban areas, as well as across burn scar regions. On Tuesday night and into Wednesday, thunderstorms are expected to develop in the High Plains of Colorado and Kansas and move into the southern Plains. Some of these areas have received above normal rainfall in the last week, elevating the chances of localized flash flooding. Additionally, there is a slight risk of severe weather in a small area of southeast Colorado and the Oklahoma Panhandle. Wix Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php