393 FXUS02 KWBC 230718 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 318 AM EDT Sun Aug 23 2026 Valid 12Z Wed Aug 26 2026 - 12Z Sun Aug 30 2026 ...Hazardous heat to continue from the Lower Mississippi Valley across the Southern Plains to the Desert Southwest... ...Overview and Guidance/Predictability Assessment... Guidance maintains an amplified and well clustered larger scale upper pattern highlighted by a strong Southwest U.S. high anchored and mean troughs near the Pacific Northwest and the east-central U.S. through this period. This pattern will not change very much this week, and as such 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 will promote scattered convection across the eastern Intermountain West and Rockies, with convection also working into the central U.S.. Shortwaves will maintain upper troughing over the east-central U.S. to favor wavy and temperature moderating frontal surges. Expect organized rain/thunderstorms as wavy fronts push into and stall over the East/Southeast and pool deep moisture and instability. A broad guidance blend seems to provide a solid forecast basis with good product and messaging continuity given favorable clustering trends further followed with latest 00 UTC guidance. ...Weather/Hazards Highlights... Under the influence of the main 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 continue to heat related illnesses. Widespread Major to Extreme HeatRisk will persist in the Southern Plains and Lower Mississippi Valley. For the Desert Southwest day maximums may easily soar to/above the 110s which could also cause heat concerns this week. Pre-frontal areas of the Southeast may be a few degrees above normal, albeit with moist dewpoints and high heat indices. Please see WPC's Key Messages for more extreme heat details. Meanwhile, lingering monsoonal moisture will stream northward on the periphery of the upper ridge to help trigger scattered, diurnally driven convection to the eastern Intermountain West and 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. WPC maintains a Marginal Risk for excessive rainfall Day 4/Wednesday and Day 5/Thursday. Shortwaves rounding the top of the ridge will trigger showers and thunderstorms across parts of the central U.S.. Some storms will be strong to severe, however the exact location/timing remains uncertain. Frontal proximity and pooling moisture/instability focus over the Central Plains prompted a WPC Marginal Risk for excessive rainfall. Expect organized rain/thunderstorm chances for the Midwest/Great Lakes midweek. Lead wavy frontal pushes will also focus widespread activity over a hot/moist/unstable East/Southeast through next weekend. WPC Marginal Risk areas Wednesday/Thursday cover parts of the Southeast and expand far up the Eastern Seaboard Thursday and seem likely to persist into 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 $$