Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EDT Wed Aug 25 2021 Valid 00Z Thu Aug 26 2021 - 00Z Sat Aug 28 2021 ...Isolated severe thunderstorms and the potential for flash flooding are forecast across the Northern Plains and Upper Midwest... ...Persistent heat and humidity continues throughout much of the central and eastern United States, while dangerously hot temperatures return to the Southwest... Rain has been a hard find this summer throughout much of the Northern Plains and Upper Midwest, but that is expected to change over the next few days as multiple rounds of showers and thunderstorms develop and traverse the north-central United States. The features responsible for the active weather include a slow-moving cold front continuing across the Upper Great Lakes tonight, with the western section of this frontal boundary lifting as a warm front over the Central Plains on Thursday. Meanwhile, an upper-level trough over the Northwest, favorable jet stream dynamics, and a plentiful amount of atmospheric moisture could lead to thunderstorms turning severe and producing several inches of rain. A few thunderstorms forming along the frontal boundary today could contain large hail and damaging wind gusts in the Central/Northern Plains through tonight, with some threat for high winds across parts of the Midwest/Ohio Valley and even across the Central Appalachians (where scattered storms could occur this evening) as well. By Thursday, more widespread thunderstorm activity is expected to be found between the Northern High Plains into the Middle Mississippi Valley, where the Storm Prediction Center has issued Slight Risks (level 2/5) of severe thunderstorms. Even though much of this region is experiencing severe to exceptional drought, multiple inches of rain could fall and lead to flash flooding concerns for both rural and urban areas of the Upper Midwest to Upper Great Lakes on Thursday and Friday. Slight Risks (level 2/4) of excessive rainfall have been issued for eastern North Dakota to central Wisconsin on Thursday and for southeastern Minnesota into much of Wisconsin on Friday in order to highlight the potential hazard. South of the aforementioned frontal boundary, much of the central and eastern U.S. will deal with a few more days of sizzling heat and humidity. An expansive upper-level ridge extending from the Southwest all the way to the East Coast will fuel above average high temperatures and high heat indices, along with air quality issues in mainly urban areas. Widespread high temperatures into the 90s will be found throughout a large section of the country, with triple digits possible over the Central/Southern Plains and Middle Mississippi Valley through Thursday. While only a handful of daily record high temperatures are forecast to fall, dozens of daily record warm minimum temperatures could be broken through the end of this week across the eastern third of the country. These warm overnight temperatures can make it extremely dangerous for those without proper air conditioning. Heat Advisories have been issued across a widespread area extending from eastern sections of the Southern Plains to parts of the Northeast. Meanwhile, dangerous heat is also making a return to the Southwest today and is expected to last through at least Friday. High temperatures here could reach close to 115F, increasing the threat of heat-related illnesses. Excessive Heat Warnings are now in effect between the Low Desert of California and southern Arizona. Elsewhere, scattered thunderstorms are possible across the Southeast and Gulf Coast over the next few days, a few of which could lead to isolated instances of flash flooding especially this evening. Farther west, Air Quality Alerts due to wildfire smoke remain in effect across parts of the Great Basin and Northern/Central Rockies. Red Flag Warnings also remain in effect across much of Wyoming and far northwest Colorado as gusty winds and low relative humidity could contribute to extreme fire behavior. Tate/Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php