Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 335 PM EDT Tue Aug 24 2021 Valid 00Z Wed Aug 25 2021 - 00Z Fri Aug 27 2021 ...Stifling heat and humidity throughout much of the central and eastern United States, dangerous heat returning to the Southwest by Wednesday... ...Scattered showers and a few severe thunderstorms possible from the northern and central Plains into the Midwest over the next few days, hit-or-miss showers and storm in the Southeast... Sizzling temperatures look to bake much of the southern tier and eastern half of the Lower 48 through mid-week thanks to an expansive area of upper level ridging that is forecast to stretch from Southern California to the East Coast. Heat Advisories have been posted from the central High Plains to the Ohio Valley while some have also been issued in parts of the Northeast. The hottest conditions are presently located in the ArkLaMiss portion of the Lower Mississippi Valley where Excessive Heat Warnings remain in place through early thins evening. As ridging aloft over the South Central U.S. bleeds into the Desert Southwest, oppressive heat is set to transpire the second half of the week in southern Arizona and far southern California. In advance of this impending heat wave, an Excessive Heat Watch has been issued for these areas beginning Wednesday morning and lasting into Friday. Some parts of the country can expect temperatures to exceed the century mark, most notably in the central High Plains and the Desert Southwest. In fact, afternoon high temps may reach up to 115F both Thursday and Friday in southeast California and southwest Arizona. While only a handful of daily high temperature records are at risk of being broken, a plethora of warm minimum temperature records are likely to fall thanks to high humidity levels keeping overnight temperatures very warm. These warm nighttime temperatures in the 70s and even near 80F can be particularly dangerous for those without access to proper air conditioning. Unfortunately, the large dome of upper level high pressure will continue to deflect cold fronts attempting to usher in cooler and more refreshing air-masses to the north for the time being, forcing much of the South and east-central U.S. to stay hot and steamy through the end of the work-week. Elsewhere, two separate rounds of showers and storms are set to impact the north-central United States over the next few days. The first wave of low pressure and its associated frontal boundaries are already responsible for segments of thunderstorms tracking through the Upper Midwest this afternoon. These thunderstorms may continue to progress east-southeast into the early evening hours and potentially produce damaging wind gusts and tornadoes across the Upper Midwest. A few isolated severe thunderstorms could develop farther south and into the Central Plains as well. By Wednesday, the same frontal boundary is expected to lift north as a warm front over the central High Plains as an approaching upper level trough over the West Coast (storm system number 2) enters the Northern Rockies. This could spell more chances for spotty severe storms throughout the northern and central High Plains. While heavy rain could cause localized flash flooding, much of this section of the country from the northern High Plains to the Upper Midwest is experiencing severe to exceptional drought and will welcome this rainfall. By Thursday however, widespread showers and storms are likely to form over the Dakotas and Upper Mississippi Valley. With recent rainfall saturating more of the ground and a better setup for heavy rainfall coming together, a day 3 Slight Risk for Excessive Rainfall has been issued for parts of these regions on Thursday. Farther south and east, typical widely scattered summer thunderstorms are anticipated across the Southeast and Gulf Coast with the main hazard associated with heavy rain. The slow movement of these pop-up thunderstorms could lead to localized instances of flash flooding. Mullinax Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php