663 FXUS02 KWBC 030711 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 311 AM EDT Thu Sep 3 2026 Valid 12Z Sun Sep 06 2026 - 12Z Thu Sep 10 2026 ...Dangerous late-summer heat continues from the central/southern Plains to the Mid/Lower Mississippi Valley into next week... ...Overview... A strong upper ridge will continue to be the focus for a long- lasting heat wave across the south-central U.S. while a slow-moving upper low will keep much of the western U.S. cooler than normal into next week. Meanwhile, monsoonal and glancing tropical moisture may lead to briefly heavy rainfall and isolated flash flooding Sunday into Monday across parts of the Southwest. Heavy rainfall potential may also increase across the north-central U.S. early next week as a strengthening low pressure system moves across the region. ...Guidance/Predictability Assessment... Models remain in good overall agreement to start the medium range period with continued troughing across the western U.S. and eastern U.S. with strong ridging in between. Towards the middle of next week, models favor the trough/upper low over the Pacific Northwest to eject eastward into the northern Plains and south-central Canada, leading to surface cyclogenesis just north of the U.S./Canada border while also suppressing and expanding the central U.S. ridge farther to the south and east. There remains some questions as to the degree of troughing that lingers downstream over the eastern U.S. as this all occurs, but current consensus seems to favor rising heights and more zonal flow over the Northeast. Upstream, models are advertising another trough/upper low developing along or just off the West Coast by Wednesday and Thursday as more energy digs into the eastern Pacific. Some uncertainty remains with the precipitation forecast across southern California and parts of the Southwest and Intermountain West Sunday into Monday as the degree of influence from tropical moisture remains in question. Models generally agree with a more westward track of Hurricane Marie, losing most of the last remaining bit of support for a more northerly track towards southern California. However, despite a more westerly track, models do still suggest at least some glancing tropical moisture associated with Marie may get drawn up into the monsoonal plume late this weekend into early next week. What models don't yet agree on is just how much of that moisture will translate to significant precipitation, as some are fairly wet and others nearly completely dry. Given the uncertainty and a recent drier trend, decided to keep the forecast more conservative for now. This allows for a lower end PoPs and precipitation amounts but with the caveat that locally heavier and more widespread amounts are not completely ruled out. ...Weather/Hazards Highlights... An unrelenting and intense late-summer heat wave will continue to bring extremely hot temperatures to much of the central/southern Plains and Mid/Lower Mississippi Valley through the weekend into next week. High temperatures well into the 90s and low 100s combined with high humidity and very warm overnight lows in the mid 70s will result in widespread areas of Major to Extreme HeatRisk and a concern for heat-related illnesses. See WPC's Key Messages for more details. Meanwhile, cooler temperatures and lower humidity in the wake of a seasonably strong cold front will continue to settle into parts of the Ohio Valley, Mid-Atlantic, and Southeast heading into Labor Day. Cooler than normal temperatures will also persist for much of the western U.S. into early next week as unsettled weather associated with a slow-moving upper low lingers over the region. In between the upper low across the Pacific Northwest and the strong ridge over the central U.S., southwesterly flow will draw monsoonal moisture into parts of the Southwest and Intermountain West this weekend into early next week. There may be a brief and glancing tropical enhancement to the monsoonal moisture courtesy of Hurricane Marie prior to tracking farther out to sea, which could lead to a low but non-zero flash flooding threat with any showers and thunderstorms that develop. With that being said, there still remains a fair amount of spread between forecast precipitation amounts, and recent trends have been drier. As a result, a more conservative forecast approach is prudent until details become clearer in the coming days. The potential for widespread showers and thunderstorms with locally heavy rainfall is becoming more likely for parts of the northern Rockies, northern Plains and Upper Midwest late this weekend into early next week as a low pressure system moves northeast across the region. A severe weather threat is also becoming more likely across portions of the northern Plains and Upper Midwest thanks to increasing moisture and instability ahead of this strengthening storm system. 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 $$