268 FXUS02 KWBC 251947 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 347 PM EDT Thu Jun 25 2026 Valid 12Z Sun Jun 28 2026 - 12Z Thu Jul 02 2026 ***Significant, dangerous heat wave begins Sunday across much of the central to eastern U.S.*** ...Pattern Overview... An anomalous upper low digging into the northwestern states will put an end to the heat wave across the Southwest and even lead to some higher elevation snow for the Montana and Idaho Rockies. This trough will spur surface cyclogenesis across the Plains with an occluded low lifting north across south-central Canada. In contrast, a building downstream upper ridge across the east-central U.S. will result in increasingly dangerous heat and humidity going into much of next week with widespread 90s across the eastern half of the country. Showers and thunderstorms will be most likely across the Gulf Coast region, the southern Rockies, and the Upper Midwest. ...Guidance/Predictability Assessment... The latest 00/12 UTC model guidance is fairly agreeable on the overall pattern through the first part of the period. Guidance indicates the upper-flow will amplify further as an upper-trough that will be digging southward over the western U.S. early this weekend is then complemented by an upper-high building over the Mississippi Valley to Southeast late weekend and into early next week. The guidance is also now well clustered depicting an initial upper-level shortwave rounding the trough and lifting northward on the western side of the ridge, leading to deep lee cyclogenesis over the northern/central Plains. Guidance agrees the progress of this system will generally be rather slow given the potent upper- high/ridge to the east through early next week. The guidance then notably diverges into the later part of the period with the evolution of this system as the 00Z ECMWF (and ECMWF AIFS) shows the upper-energy/surface low lifting northward while the 12Z GFS/CMC progress eastward and generally shear out while rounding the top of the upper-ridge, the GFS first then the CMC. Details are not surprisingly less clear in the ensemble means though they do tend to support a middle ground similar to the GFS as opposed to the other deterministic guidance. The CMC has also tended to trend weaker with the upper-high expanding over the Miss/Ohio Valleys and Southeast compared to the other guidance and the means. The updated WPC forecast initially used a composite blend of the 00Z ECMWF/ECMWF AIFS/UKMET and 12Z GFS/CMC given the good overall agreement. The contribution from the deterministic guidance was significantly reduced aside from the GFS for the latter half of the period and replaced by a contribution from the GEFS/ECens/CMC means given the noted diverging solutions from the ECMWF/ECMWF AIFS/CMC. ...Weather/Hazards Highlights... There should be an overall decrease in rainfall coverage going into Sunday across most of the country compared to the short range forecast period. There will likely be some showers and storms near the coastal Carolinas as a weak wave of low pressure develops offshore. Rain and mountain snow over central and western Montana should still be ongoing, with several inches of snow accumulation possible for the highest mountain ranges. Looking ahead to Monday/Tuesday, a corridor of showers and storms, some of which could be heavy, are forecast to develop from Nebraska to the Upper Peninsula of Michigan ahead of the cold front crossing the Upper Midwest. Elsewhere across the country, some thunderstorms are likely to develop in the vicinity of the dryline across western Texas and eastern New Mexico for the first half of the week, with a higher trend compared to previous forecasts. Scattered showers and thunderstorms are expected from the central Gulf Coast to the Florida Peninsula with moisture increasing south of the upper ridge, with most of these happening during the afternoon and evening hours. A temperature dichotomy will exist across the country starting this weekend as the deep upper trough heralds the arrival of much cooler conditions starting across the Pacific Northwest and northern Rockies, with highs running on the order of 15-25 degrees below late June averages. This will likely be cold enough to come close to some new daily record low temperatures. The opposite will hold true across much of the Plains, Midwest, Southeast, and Mid- Atlantic as the building upper-ridge brings a significant, dangerous heat wave beginning Sunday. Highs in the 90s are expected as far north as the Great Lakes and Minnesota, and 100s for much of Texas. Some 100+ degree readings are also possible for portions of the Southeast by Thursday. Heat indices approaching 110-115 degrees are possible from the Mid-South to the central Gulf Coast where the combination of heat and high dewpoints will be greatest. Overnight lows will also be quite warm, with some record high minimums possible, bringing little to know relief from the heat. Putnam/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 $$