Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 350 PM EDT Tue Aug 27 2024 Valid 00Z Wed Aug 28 2024 - 00Z Fri Aug 30 2024 ...Record heat on tap for the Ohio Valley, Tennessee Valley, southern Appalachians and Mid-Atlantic, but relief on the way... ...Active thunderstorms, heavy rains, flash flooding and severe weather possible over large portions of the north central to east central U.S... ...Fire weather threat for portions of the Northwest/Northern Rockies, along with early season high elevation snow... Much above average temperatures will continue over the next few days across a large portion of the nation from the Central to Southern Plains, east into the Mississippi Valley, Ohio Valley, Southeast and Mid-Atlantic. Across much of these areas, high temperatures are forecast to be from 10 to 15 degrees above average. This will result in the potential for record high temperatures across much of the Ohio and Tennessee Valleys into the Southern Appalachians and Mid-Atlantic on Wednesday and across the Ohio and Tennessee Valleys and Southern Appalachians on Thursday. The combination of the much above average temperatures and continued high levels of humidity will produce maximum heat indices on Wednesday and Thursday in the 105 to 110+ degrees F range across these areas, producing major to extreme heat risks through the Ohio/Tennessee Valleys into the Mid-Atlantic. Excessive Heat Warning and Heat Advisories are currently in effect across much of these areas, affecting over 77 million people. Some relief is in store for portions of the U.S. on Wednesday that have had very hot temperatures the past few days. A cold front will be pressing south out of the Upper Great Lakes into the Mid-West tonight, bringing relief to the very hot recent temperatures for southern Michigan into central to southern Wisconsin, northern to central Illinois, eastern Iowa into northeast Missouri. This front will continue to press southeastward Wednesday night bringing relief by Thursday to the heatwave for the Mid-Atlantic region into the Upper Ohio Valley. The trend of shrinking areal extent of major to extreme heat risks will accelerate by the beginning of the holiday weekend across large portions of the nation. The frontal boundary sinking southeastward from the Upper Mississippi Valley/Upper Great Lakes region and a second strong front moving from the Northern Rockies/North High Plains tonight into the Northern to Central Plains/Upper Mississippi Valley region Wednesday into Thursday will be the focus for areas of active thunderstorms. With moisture values expected to be much above average along and ahead of each of these fronts, locally heavy rain and isolated flash flooding is possible from the Great Lakes into the Ohio Valley late this afternoon into early Wednesday, and across the Ohio Valley into the Mid-Atlantic, and portions of the Northern Plains into the Upper Mississippi Valley late Wednesday into Thursday. In addition to the heavy rain/flash flood threats, these thunderstorms may also produce severe weather across these areas, with large hail and high winds the greatest threat, with a lesser threat for tornadoes. The strong front pushing east form the northwest late this afternoon will produce strong gusty winds in its wake over the Northern Great Basin into the Northern Rockies. These windy conditions, combined with low relative humidities will produce fire weather threats into Wednesday , with Red Flag warnings in effect across these areas. The cold temperatures in the wake of this strong front will also support snowfall potential above 5000 feet in the northern Rockies of Montana where snowfall amounts of 3 to 6 inches are possible on Wednesday. Oravec Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php