889 FXUS02 KWBC 020816 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Wed Sep 2 2026 Valid 12Z Sat Sep 05 2026 - 12Z Wed Sep 09 2026 ...Dangerous late-summer heat wave will shift into the south- central U.S. this weekend into early next week... ...Overview... The focus for intense late-summer heat will shift into the south- central U.S. this weekend into next week while a cold front brings relief to the southern Mid-Atlantic and Southeast after one more hot day and potential severe weather on Saturday. In contrast, a slow-moving upper low spinning over the Pacific Northwest should keep much of the region cooler then normal and unsettled through early next week. Meanwhile, surging monsoonal moisture and a possible tropical connection may lead to heavier rainfall and localized flash flooding this weekend across parts of the Southwest. ...Guidance/Predictability Assessment... Models are generally in good agreement with the large scale pattern through most of the weekend, featuring persistent troughing and a slow-moving upper low over the West Coast/Pacific Northwest, stout ridging across the central U.S., and lingering troughing across the Northeast and along the East Coast. This general pattern mostly persists into next week, though guidance begins to differ on the evolution of the troughing/upper low in the Northwest and whether or not it reinforces itself or advances eastward and helps suppress the central U.S. ridge. The WPC forecast continues to favor a non-NCEP blend given some lingering influences of Tropical Storm Marie tracking a little too far north compared to consensus, as well as being too strong with a digging shortwave over south-central Canada which suppresses the central U.S. ridge too quickly. The initial preferred blend was a mix of non-NECP deterministic guidance and AI guidance led by the EC-AIFS and the AI-GFS. Later on the period, more weighting was placed on the EC and GEFS ensemble means which preserved large scale features while smoothing smaller scale differences. ...Weather/Hazards Highlights... A dangerous late-summer heat wave will continue to bring extremely hot temperatures to the central U.S. through the weekend into next week as a large mid/upper ridge remains centered over the region. 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. Hot conditions are also forecast across the southern Mid-Atlantic and Southeast for one more day on Saturday, but a cold front will bring some relief behind a passing cold front Sunday into next week. Please continue to see WPC's Key Messages for more details on this long lasting heat wave. Meanwhile, cooler than normal temperatures will remain in place across the Northwest through early next week as persistent clouds and showers associated with deep troughing and a slow-moving upper low remain entrenched across the region. High temperatures will mostly top out in the 50s, 60s, and 70s, which is roughly 10-15 degrees below seasonal norms. The frontal system that will bring relief from the heat across parts of the eastern U.S. this weekend will first interact with sufficient moisture and instability to produce locally heavy rainfall and possible severe weather across the southern Mid- Atlantic into the Carolina Piedmont on Saturday. The strongest storms will be capable of producing damaging winds, with hail and perhaps an isolated tornado not ruled out. Storms could also contain heavy rain rates that could lead to localized flash flooding, mainly in urban areas. In between the upper low across the Pacific Northwest and ridge over the central U.S., southwesterly flow will usher in surges of monsoonal moisture across parts of the Southwest and Intermountain West this weekend into early next week. This highly anomalous moisture will support the development of showers and thunderstorms, with some possible tropical connection to Tropical Storm Marie leading to a low but non-zero flash flooding threat. While the current thinking still favors a track for Marie that stays far away from southern California, there is still a threat of tropical moisture enhancing monsoonal rainfall and thus leading to additional concerns for flash flooding. See the latest Day 4 and 5 EROs for more details and stay tuned to NHC and WPC for future updates. 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 $$