Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Thu Aug 24 2023 Valid 12Z Sun Aug 27 2023 - 12Z Thu Aug 31 2023 ***Still remaining hot and humid for the Gulf Coast region through early next week with some places likely recording the warmest August on record*** ...Synoptic Overview... Welcomed relief from the extreme heat is in store for the north-central U.S. by the weekend as the ongoing major late summer heatwave abates and the upper ridge is suppressed to the south. The areal coverage of excessive and record-breaking heat will shrink with it, becoming more limited to the Gulf Coast states by the weekend where additional daily record highs are likely. The upper trough that is forecast to amplify over the northeastern quadrant of the country next week not only will be responsible for bringing the cooler temperatures but also a threat of heavy rain for the central High Plains this weekend, followed by the Carolinas during the first half of next week. ...Guidance Evaluation/Predictability Assessment... The 00Z model guidance suite remains in very good agreement across the continental U.S. through Sunday with generally above average forecast confidence on the synoptic scale. Therefore a multi-deterministic model blend suffices as a starting point in the forecast process for fronts/pressures through Monday night. Looking ahead to Tuesday and Wednesday, the model guidance is still in overall decent agreement, and the guidance has converged on timing for the strong upper trough developing over the Great Lakes/Interior Northeast by Wednesday, and there is improved model consensus for Franklin as this system remains well off the East Coast. Ensemble means accounted for about 40% of the model blend by next Thursday, whilst still keeping sizable portions of the GFS/ECMWF solutions. ...Weather/Hazards Highlights... Showers and thunderstorms are expected to be prevalent from eastern Colorado and extending into portions of eastern New Mexico and northwestern Texas Sunday and into Monday as a couple of convective complexes are likely to develop. A Marginal Risk area is in effect for both of these days where some slow moving storms could develop and produce localized instances of flooding. Across the eastern U.S., the cold front will intercept a moist and unstable airmass across the Carolinas with scattered to numerous showers and storms expected to develop, and a Marginal Risk area is in effect from the southern Appalachians to the South Carolina coast. Unsettled weather conditions are likely to continue across portions of the Southeast U.S. going into the middle of next week, with convection increasing across much of Florida. Tropical convection appears to stream toward the Florida Peninsula from the southwest as the National Hurricane Center is monitoring the potential for a tropical system to develop over the eastern Gulf of Mexico early next week, but for now a Marginal Risk is valid for roughly the southern third of Florida on Monday to account for this potential. Elsewhere, showers and a few storms are likely from the Great Lakes to New England for the first half of the week, and Washington state may also get some beneficial rainfall by Tuesday and Wednesday. Although the heatwave will have concluded across the Midwest and Ohio Valley, it will still be quite hot and uncomfortable from Texas to South Carolina this weekend, with widespread 100+ degree highs expected on Sunday along and south of the Interstate 20 corridor. This may establish additional daily record highs and probably secure the hottest August on record for many Gulf Coast and Deep South cities. The heat finally abates a little across the Gulf Coast region going into Tuesday and Wednesday with mainly 90s for highs expected for these same areas, but still remaining a few degrees above average with no sign of fall-like weather anytime soon. Unfortunately heat builds again across the lower elevations of the Desert Southwest with some 110s likely by the weekend and early next week, but this should also abate some by Wednesday and beyond. Elsewhere, temperatures will be pleasant across much of the northeastern quadrant of the nation with highs mainly in the 70s and 80s and comfortable humidity levels, and 60s closer to the Canadian border. Hamrick Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw