Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 353 AM EDT Sun Aug 19 2018 Valid 12Z Sun Aug 19 2018 - 12Z Tue Aug 21 2018 ...Heavy rainfall and strong thunderstorms expected to impact parts of the Plains and Mississippi Valley... ...Air quality will remain a concern across portions of the Western U.S. and the Upper Midwest... A low pressure system in the southern Plains will lift into the central Plains and middle Mississippi Valley today. Heavy rain already impacting the central and southern Plains will continue to move eastward today across these areas and move into the middle and lower Mississippi Valley by this evening. Farther north, a cold front will press southward along the northern Plains and Upper Mississippi Valley. Showers and thunderstorms are expected to develop along and ahead of the front--which will be capable of producing flash flooding. A slight risk of flash flooding is possible for parts of northern Plains in addition to portions of the central and southern Plains. There is also a marginal risk of severe weather for the southern Plains and into the lower Mississippi Valley. As this system slides from the Mississippi Valley into the Ohio Valley, showers and thunderstorms will develop in Iowa on Monday afternoon and will progress into southern Wisconsin and northern Illinois. By Tuesday morning, showers and thunderstorms will increase throughout the Great Lakes, Ohio Valley southward into the lower Mississippi Valley. Fire weather continues to remain a concern across the western U.S. The combination of high winds, low humidities, and the threat of low precipitating thunderstorms may contribute to igniting wildfires. Due to the ongoing wildfires, Air Quality Alerts remain in place for the Pacific Northwest, northern Montana and a small portion of the Southwest due to smoke pollution. In addition, wildfires in Canada are also advecting smoke southward across the Upper Midwest, resulting in Air Quality Alerts for much of Minnesota as well. Reinhart Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php