684 FXUS02 KWBC 280610 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 210 AM EDT Fri Aug 28 2026 Valid 12Z Mon Aug 31 2026 - 12Z Fri Sep 04 2026 ...Dangerous heat to broadly expand from the central and southern Plains to the Midwest, Southeast, and Deep South next week... ...Pattern Overview... An intensifying late summer heat wave will bring extreme temperatures to the central/southern Plains before expanding to the Midwest and South next week. Meanwhile, surges of monsoonal moisture will continue to support daily showers and thunderstorms across portions of the Southwest and the Intermountain West/Rockies with localized flash flooding possible. Farther north, a progressive series of storm systems will bring active weather to the Pacific Northwest, along with the potential for severe weather and heavy rain threats farther downstream from the northern Plains and Upper Midwest to the Northeast. ...Guidance/Predictability Assessment... The latest available model guidance continues to have a relatively good handle on the overall large scale pattern through the medium range period, featuring several bouts of troughing across the Pacific Northwest, a potent shortwave/closed low tracking eastward along the U.S./Canada border, and an elongated upper ridge centered over the Central and Southeast U.S. (with an upper low trapped underneath along the Gulf Coast). Timing and positional differences start to increase beyond Day 5, so the WPC forecast utilized a composite blend of deterministic and machine learning guidance (with a preference toward the EC/EC-AIFS) before then. After Day 5, the blend gradually shifted more weighting (up to 50%) towards the EC/GEFS ensemble means to mitigate the spread for Days 6 and 7. ...Weather/Hazards Highlights... A sprawling upper ridge expanding from the Central U.S. to the Southeast U.S. will focus an intensifying and long-lasting late summer heat wave from the central/southern Plains to the Midwest, Southeast, and Deep South next week. High temperatures climbing well into the 90s and 100s combined with high humidity and very warm overnight lows in the 70s to near 80 will result in widespread areas of Major to Extreme HeatRisk, increasing the threat of heat related illnesses. Please see WPC's Key Messages for more details. Surges of monsoonal moisture ahead of persistent Pacific Northwest upper troughing and Central/Eastern U.S. upper ridging will continue to fuel daily scattered afternoon and evening showers and thunderstorms across portions of the Southwest, Intermountain West, and Rockies through most of next week. Some thunderstorms are likely to produce heavy rainfall which may lead to isolated instances of flash flooding for more vulnerable areas like burn scars, slot canyons, and urban areas. A series of disturbances tracking into the Pacific Northwest and along the U.S./Canada border will highlight a period of active weather across the northern half of the country over the course of next week. A potent shortwave/closed upper low moving from south- central Canada eastward to northern New England and vicinity will lead to the development of a strengthening surface low and frontal system with the potential to bring heavy rainfall and severe weather across parts of the northern Plains, Upper Midwest, Lower Great Lakes, Ohio Valley and the Northeast. Meanwhile, persistent troughing and reinforcing shortwaves crashing into the Pacific Northwest coupled with a possible atmospheric river may result in a period of heavier rainfall for coastal and mountain regions of Washington and Oregon mid to late next week. Additionally, some snow can't be ruled out across the highest elevations of the Cascades as a pocket of colder air aloft moves overhead. Elsewhere, dissipating frontal boundaries and a slow-moving upper low will likely contribute to a lingering threat for locally heavy rainfall and isolated flash flooding concerns over portions of the Gulf Coast, Southeast, and Florida next week. Miller 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 $$