389 FXUS02 KWBC 081850 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Tue Sep 8 2026 Valid 12Z Fri Sep 11 2026 - 12Z Tue Sep 15 2026 ...Prolonged late-summer heat wave lingers for the southern Plains through next weekend... ...Overview... A shortwave will push a cold front from the Northern Plains to the Northeast Friday to Sunday, with increasing rain chances along and ahead of it. Behind this, consensus is increasing for a compact closed low to 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. Upper level ridging will meanwhile persist across the southern tier, maintaining hot conditions for the south-central U.S. and monsoonal moisture for the Southwest. Another shortwave moves into the Northwest next Tuesday. ...Guidance/Predictability Assessment... The latest model guidance remains generally well clustered with a pattern featuring a progressive northern stream this weekend and and into early next week. Following the departure of an initial upper-trough/surface cold front off the East Coast mid- to late week, another upper-wave is expected to pass across southern Canada and the northern tier bringing a cold front through the norther/central Plains and Midwest and to the Northeast late this week and through the weekend. The progression of this feature is well captured on a broader scale by all the guidance. Thereafter, guidance begins to diverge a bit handling the next upper-wave upstream dropping southward from the northeastern Pacific and amplifying/closing off over the northwestern U.S. The UKMET was more progressive and the AIGFS slower while the ECMWF/GFS/ECMWF AIFS/CMC initially remain better clustered late weekend. The progression of the ECMWF/GFS/ECMWF AIFS/CMC begin to diverge a bit more as the system moves out onto the Plains and to the Midwest, though remain reasonably well clustered into early next week and within the envelope of the means especially at this later time range. Smaller-scale differences on boundary placement will impact the timing/footprint of QPF though much of the guidance was in agreement on potentially very heavy rainfall. Meanwhile, the upper- wave downstream begins to amplify along/off the East Coast by Tuesday particularly in the CMC but also somewhat in the ECMWF AIFS, which would potentially bring cooler temperatures down the East Coast, though the GFS/ECMWF and ensemble means don't show such a degree of amplification. The updated WPC forecast used a composite blend of the deterministic and AI guidance through the first part of the period given the noted good agreement. The UKMET and then AIGFS and CMC are removed as their solutions diverge relative to the second noted upper-wave as well as the downstream amplification of the first upper-wave along the East Coast. A contribution from the ECens and GEFS means replaced this guidance with the other deterministic guidance falling within this envelope. The NBM was a good starting point for the forecast grids with only some minor modifications made to reduce some higher QPF amounts in the late Saturday to late Sunday time frame where only the GFS was particularly aggressive with amounts early in the approach of the northern tier system this weekend. ...Weather/Hazards Highlights... The long duration heat wave is expected to linger over the Mid/Lower Mississippi Valley and southern Plains into the medium range period with widespread Major to Extreme HeatRisk. Key Messages remain in effect with several record minimum and maximum temperatures in the forecast. There continues to be a trend for relief to northern areas by the weekend, confining the greatest heat threat to the southern Plains. Above normal heat may also build briefly across the Southwest and parts of California into late week as upper level ridging extends into the region. 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 cold front will be exiting the Northeast by Friday, but lingers across the Southeast supporting daily showers and thunderstorms, with locally heavy rainfall possible. Behind this, another front will bring rain to the Midwest and into the Northeast Friday- Sunday. Severe weather will be possible with storms from the central Plains to the Upper Midwest Friday. The main focus for precipitation during the period 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 by Saturday but 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. 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 $$