Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 PM EDT Thu Aug 24 2023 Valid 12Z Sun Aug 27 2023 - 12Z Thu Aug 31 2023 ***Hot and humid conditions will persist for the Gulf Coast region through early next week with some places likely recording the warmest August on record*** ...Synoptic Overview... Relief from ongoing record-breaking heat wave will finally arrive this weekend for much of the Central U.S. as the upper level ridge is suppressed to the southwest. Hot and humid conditions will linger longer along the Gulf Coast, lasting through Monday, and multiple daily record high max and min temperatures will be possible. Upper level troughing will strengthen over the eastern half of the nation, driving several frontal systems that will create a heavy rainfall threat in parts of the Central High Plains, Mid-Mississippi Valley, and the Carolinas. Rain will also return to the Pacific Northwest mid-next week as an upper level low moves onshore. The National Hurricane Center is also monitoring a disturbance in the Caribbean that may bring heavy rainfall to parts of the Southeast late next week. ...Guidance Evaluation/Predictability Assessment... Model guidance remains in good agreement on the synoptic pattern over the period, especially the ensemble means. Slight differences in the positions and tracks of low pressure systems appear in the deterministic solutions, but are relatively minor. A pure deterministic model blend with nearly even amounts of the CMC/GFS/ECMWF/UKMET was used for the first half of the period to produce a middle of the road solution, and ensemble means were blended with the deterministic GFS/ECMWF for the second half of the period. ...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 of Excessive Rainfall is in effect for both of these days where some slow moving storms could develop and produce localized instances of flooding. In the East, a stalled frontal boundary along the Southeast and Gulf Coasts and an approaching cold front from the north will create rain chances early next week in the Mid-Mississippi Valley on Sunday and in the Carolinas Sunday and Monday. There are Marginal Risks of Excessive Rainfall in effect for these areas as well. The National Hurricane Center is monitoring the potential development of a tropical system that could bring a heavy rain threat to parts of the Southeast mid-next week. There is still a significant amount of uncertainty concerning the heavy rainfall potential, but we will be monitoring the situation closely. Tropical moisture ahead of the system will reach South Florida on Monday, and there is a Marginal Risk of Excessive Rainfall in effect. The rainfall threat is forecast to spread north through mid-week. 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 as a frontal system moves onshore. 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. This may establish additional daily record highs and probably secure the hottest August on record for many Gulf Coast and Southern cities. The heat finally abates a little across the Gulf Coast region going into Tuesday and Wednesday with near to just above normal highs expected. Unfortunately, heat is forecast to build 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. Dolan/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