Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 354 AM EDT Tue Jul 27 2021 Valid 12Z Tue Jul 27 2021 - 12Z Thu Jul 29 2021 ...There is a Slight Risk of excessive rainfall over parts of the Southeast through Wednesday morning... ...There is a Slight Risk of excessive rainfall over parts of the Upper Midwest/Upper Great Lakes Wednesday through early Thursday... ...There is a Slight Risk of severe thunderstorms over parts of the Upper Midwest and the Lower Great Lakes through Wednesday morning... ...Excessive Heat Warning over parts of the Northern High Plains; Heat Advisory over parts of the Lower Mississippi Valley/Southern Plains, Northern/Central Plains, and the Northern High Plains... A front extending from the Northeast across the Great Lakes into the Northern High Plains will have multiple waves of low pressure that will travel along the boundary as the front slowly settles southward to the Mid-Atlantic roughly westward to the Northern Rockies by Thursday. Showers and thunderstorms will develop along and near the boundary, some of which may become severe. Therefore, the SPC has issued a Slight Risk of severe thunderstorms over parts of the Upper Midwest and the Lower Great Lakes through Wednesday morning. The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and minimal risk of tornadoes. The severe thunderstorm threat increases on Wednesday into Thursday over the Upper Great Lakes/Upper Mississippi Valley with the SPC hoisting another Slight Risk of severe thunderstorms and the WPC introducing a Slight Risk for flash flooding. Meanwhile, a front extending from the Mid-Atlantic across the Ohio/Tennessee Valleys into the Northern Plains will slowly dissipate this evening. South of the front, tropical moisture will extend from the Southeast to parts of the Lower Mississippi Valley and the Southern Plains. An upper-level impulse over the Southeast will trigger showers and thunderstorms over the region yielding heavy rain. Therefore, the WPC has issued a Slight Risk of excessive rainfall with these thunderstorms through Wednesday morning. The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams. While showers and thunderstorms will continue across the Southeast to the Southern Plains through midweek, the excessive rainfall threat will lessen Wednesday into Thursday. Furthermore, the excessive rainfall threat over the West will diminish as the moisture associated with the monsoon has weakened. Showers and thunderstorms will continue over the Southwest, Central/Southern Rockies, and Great Basin through Thursday, becoming more diurnal. Over the Northwest, there is an Excessive Heat Warning over parts of the Northern High Plains, where temperatures will rise into the 100s. Furthermore, Heat Advisories are currently in effect for portions of the Lower Mississippi Valley/Southern Plains, Northern/Central Plains, and the Northern High Plains. Moreover, several regions have Air Quality Alerts due to wildfires over the Northwest into the Northern Rockies. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php