688 FXUS02 KWBC 090642 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Wed Sep 9 2026 Valid 12Z Sat Sep 12 2026 - 12Z Wed Sep 16 2026 ...Prolonged late-summer heat wave lingers for the southern Plains into early next week... ...Overview... A shortwave will push a cold front from the Upper Midwest to the Northeast this weekend, with increasing rain chances along and ahead of it. Behind this, a compact closed low will move into the Northwest by Saturday, progressing eastward into the Northern Plains by Monday. Moderate to heavy rainfall looks increasingly likely across the Upper Mississippi Valley to Great Lakes Sunday and Monday, with some winter weather potential for the Northern Rockies. Meanwhile, upper level ridging will persist across the southern tier, maintaining hot conditions for mainly the Southern Plains and monsoonal moisture for the Southwest. Another potentially deeper shortwave moves into the Northwest next Tuesday or Wednesday. ...Guidance/Predictability Assessment... The latest model guidance continues to show good overall agreement on the large scale pattern and evolution through most of the period, but plenty of uncertainty in the details. The most impactful system will be a closed low over the Northwest this weekend, moving over the Northern Rockies and Plains Sunday into Monday. This pushes a strong cold front through the northern tier, with guidance generally showing better agreement on the timing compared to prior runs. A general deterministic model compromise seemed to work well for this. Downstream, a shortwave clipping the Great Lakes continues to show more amplification over the Northeast and off the East Coast this weekend in CMC runs (and to some extent the EC-AIFS as well) than the consensus/ensembles would suggest. By next Tuesday or Wednesday, another shortwave drops in the Pacific Northwest with notably more uncertainty. Both the GFS and ECMWF are stronger showing possible closed lows next Wednesday over Washington, vs the CMC and EC-AIFS are a bit more progressive and open with the wave. The WPC forecast blend trended more towards the ensemble means by Days 6 and 7 to help mitigate these differences will may take days to fully resolve. ...Weather/Hazards Highlights... The long duration heat wave is expected to linger over the Southern Plains and at times into the Mid-Mississippi Valley through the medium range with widespread Major to Extreme HeatRisk. Key Messages remain in effect with several record minimum and maximum temperatures in the forecast. This southern ridge will also help support monsoonal moisture and daily shower and thunderstorm chances for the Four Corners region much of the period. There looks to be an uptick in the influx of moisture early next week as the southern ridge shifts eastward with a greater chance for locally heavy rainfall/flash flooding. A lingering front over the Southeast and Mid-Atlatic states will continue a daily threat for showers and thunderstorms, with locally heavy rain. Another front will bring rain from the Central U.S. into the Northeast, with some elevated flash flood threat across parts of the Central Plains to Mid-Mississippi Valley on Saturday. The main focus for precipitation during the period though will be across the Northwest into the Northern U.S. this weekend and early next week as an upper low moves through. A strong cold front will enhance rainfall chances ahead of it, with moderate to heavy rainfall potential increasing especially into Sunday and Monday across portions of the Plains into the Midwest. Wintry weather will also be possible in the northern Rockies this coming weekend as cooler air moves in behind the cold front. Showers will move with the front into the Ohio Valley and Northeast early next week. Santorelli 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 $$