Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 406 PM EDT Fri Aug 17 2018 Valid 00Z Sat Aug 18 2018 - 00Z Mon Aug 20 2018 ...Slight risk of severe thunderstorms and flash flooding for the Northeast with heavy rainfall impacting areas from the Mid-Atlantic to the Southern Plains... ...Heavy rainfall will begin impacting portions of the Plains this weekend... ...Air quality will remain a concern this weekend across much of the Northwestern U.S. and also parts of the Upper Mississippi Valley... Active weather will impact locations from the Northeast to the Southern Plains this evening as a frontal boundary drifts slowly eastward. Deep southerly flow ahead of this system will pull anomalous moisture northward to create an environment conducive to heavy rainfall and possible severe weather. Expect widespread scattered showers and thunderstorms to continue all across much of the Eastern states and back into the lower Mississippi Valley and Southern Plains. The best chance for severe weather and excessive rainfall/flash flooding will be in the Northeast as the main surface low moves through this region tonight. While the cold front should exit the Northeast early Saturday, the boundary is forecast to linger across the Mid-Atlantic, the Tennessee Valley, and the Southern Plains. This will continue the threat for showers and thunderstorms, along with localized heavy rainfall and severe weather, across the Mid-Atlantic and much of the southern tier states. Both SPC and WPC have marginal risks highlighted on their convective and excessive rainfall graphics, respectively. Monsoonal moisture will continue across the Southwest with diurnally driven showers and thunderstorms leading to a daily, marginal to slight, threat for heavy to excessive rainfall and flash flooding. To the north, a system pushing into the Central U.S. will increase the heavy rainfall threat for the central and southern high Plains and Plains. With significant moisture in place, excessive rainfall and flash flooding will be a concern, and WPC has portions of the High Plains in a slight risk for Saturday, pushing eastward on Sunday. Out west, dry thunderstorms and active fire weather will continue this evening, with numerous Red Flag Warnings in effect across the northern Intermountain West. Air quality will remain a concern through the weekend as well with heavy smoke from ongoing fires lingering across the Northwest and California. The latest satellite imagery indicates smoke from these fires also propagating downstream into parts of the far northern Plains and the Upper Mississippi Valley with air quality alerts in effect for much of Minnesota. Santorelli Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php