122 FXUS02 KWBC 091943 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 343 PM 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... While the guidance was generally agreeable on the overall pattern through the period there were some notable timing/evolution differences on the main features. An initial upper-trough over south-central Canada and along the northern tier of the U.S. will progress eastward towards the East Coast through the weekend. The guidance is initially agreeable on the progression before the CMC and to a lesser degree the AI guidance shows the upper-trough amplifying along the East Coast. The GFS/ECMWF/UKMET and ECens/GEFS means do not show this amplification and maintained broader ridging across the southeastern U.S. into the southwest Atlantic. Meanwhile, upstream, guidance agrees another upper-wave will drop southward into the Interior West and amplify as a closed low develops into the weekend. All guidance is also in agreement the upper-low will then lift northeastward across the central/northern Plains and open into a wave over the Midwest early to mid-next week. However, the same guidance camps that differed on the amplification to the east also differ on the evolution of this feature. The GFS/ECMWF/UKMET are more amplified over the western U.S. and then bring the opening wave/accompanying surface system across the Plains and through the Midwest faster than the CMC and AI guidance. The GEFS/ECens means favor the faster progression of the GFS/ECMWF/UKMET initially before slowing as the system progresses into Canada. All guidance also agrees another upstream upper-wave will follow into the northwestern U.S. by mid- week though again diverge on progression with the CMC faster than the GFS/ECMWF. The updated WPC forecast favored a blend of the GFS/ECMWF/UKMET through the early part of the period given their solutions better fell within the envelope of the means and maintained better WPC forecast continuity. A 50% contribution of the ECens/GEFS means is included for the latter part of the period as the time-limited UKMET is removed and the ECMWF/GFS start to progress a bit faster with the system over the Midwest as it moves into Canada. The NBM looked like a reasonable starting point with only minimal adjustments made to lower temperatures a bit following preferred frontal progression over the Interior West and then along the northern tier. The QPF forecast also looked reasonable with the footprint/amounts in line with the preferred ensemble means and deterministic guidance, particularly with respect to heavier rainfall expected over the Upper Midwest during the Sunday to Monday timeframe. ...Weather/Hazards Highlights... Heat will remain in the forecast into the Medium Range period across much of the southern tier of the country with broad upper- ridging in place. The greatest coverage of Moderate to Extreme Heat Risk will focus on the southern Plains/Texas into the Lower Mississippi Valley. 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 possible particularly across the Piedmont Saturday. 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. Additional heavy rainfall is likely to the west under the core of the upper-low across the northern High Plains of Montana Sunday. 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. Putnam/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 $$