FXUS02 KWNH 240729 PREEPD Preliminary Extended Forecast Discussion NWS Weather Prediction Center College Park MD 328 AM EDT Mon Aug 24 2026 Valid 12Z Thu Aug 27 2026 - 12Z Mon Aug 31 2026 ...Hazardous Heat continues from the Desert Southwest to the Southern Plains... ...Overview... The upper level pattern will feature troughing in the Northwest and East with a strong ridge anchored over the Southwest. The ridge will flatten late this week as upper level troughing strengthens over the Northwest, resulting in some areas seeing relief from the ongoing heat wave, but hazardous heat will persist for the Desert Southwest and southern Plains. Moisture on the western periphery of the ridge will continue to support daily monsoonal convection across the Intermountain West. Meanwhile, several frontal systems will push through the upper troughs, bringing showers/thunderstorms from the northern/central Plains to the East/Southeast U.S.. ...Guidance/Predictability Assessment... Guidance agrees that an ongoing upper pattern highlighted by a strong Southwest U.S. to southern Plains high/ridge anchored by mean troughs near the Pacific Northwest and the east-central U.S. will persist over the next week. This will continue to support a protracted heatwave with Hazardous Heat threats from the South- Central to Southwest U.S.. Along the ridge's periphery monsoonal moisture may promote scattered convection from the Southwest to the Rockies, with convection also working into the north-central U.S.. Shortwaves will maintain upper troughing over the east-central U.S. to favor wavy and temperature moderating frontal surges. Expect unseasonally well organized rain/thunderstorms daily as wavy fronts push into and stall over the East/Southeast and pool deep moisture and instability. A broad model/ensemble mean and machine learning guidance blend seems to provide a solid forecast basis with good product and messaging continuity given favorable clustering trends that have further improved with the latest 00 UTC guidance. ...Weather/Hazards Highlights... Still under the influence of the upper high/ridge, daily maximum temperatures across the southern Plains will continue to rise into the 90s and 100s with oppressive heat indices. Record- breaking warm overnight temperatures across the southern tier will further limit recovery from the heat, especially given heatwave longevity which may result in heat related illnesses. Conditions will improve this week for the Lower Mississippi Valley, but widespread Major to Extreme HeatRisk will persist in the southern Plains. For the Desert Southwest, daytime max temperatures are forecast to soar into the 110s, which will create heat concerns this week. Pre- frontal areas of the Southeast may be a few degrees above normal, but forecast precipitation and cloud cover will help keep heat in check. Please see WPC's Key Messages for more extreme heat details. Monsoonal moisture streaming northward on the periphery of the upper ridge will fuel scattered, diurnally driven convection from the Southwest to the Rockies. Individual cells may lead to isolated instances of flash flooding for sensitive locations such as burn scars, favored terrain like slot canyons, and urban areas. There is a Marginal Risk for parts of these areas in the WPC Day 4/Thursday and Day 5 Friday Excessive Rainfall Outlooks (EROs). Shortwaves rounding the top of the ridge to the east-central U.S. mean upper trough will periodically trigger showers and some strong thunderstorms from the northern and central Plains to the Midwest this week. A Marginal Risk ERO covers this threat. Downstream, elongated ERO Marginal Risk areas are highlighted for portions of the Southeast and Mid-Atlantic that may see repeated rounds of locally heavy precipitation as wavy frontal boundaries approach and ultimately stall over these regions. Later period, a stronger frontal system will push across an unsettled Northwest and north-Central U.S., bringing increasing precipitation chances and potentially heavy rainfall to the Plains and Midwest. Warm, southerly flow on the southern side of the system may increase heat for the south-central U.S. next weekend. Schichtel 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 $$