439 FXUS02 KWBC 071741 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 PM EDT Mon Sep 7 2026 Valid 12Z Thu Sep 10 2026 - 12Z Mon Sep 14 2026 ...Prolonged late-summer heat wave lingers for the southern Plains through next weekend... ...Overview... An upper level trough will push across the Northeast late this week, accompanied by a cold front that will bring precipitation chances from the Northeast to the Mid-Mississippi Valley. Upper level troughing will also extend into the Northwest late this week and be reinforced by shortwave energy next weekend. This feature will gradually push east through early next week, resulting in unsettled weather from the Northwest to the Plains, with some winter weather potential for the northern Rockies. Meanwhile, upper level ridging will persist across the southern tier, maintaining hot conditions across the south-central U.S. ...Guidance/Predictability Assessment... Model guidance remains in good agreement on the synoptic scale pattern through the end of the week, with relatively flat/zonal upper level flow leading to some minor timing differences. Model spread increases significantly next weekend into early next week as the models struggle to resolve upper level interactions between various lows and troughs extending from Canada into the northern tier of the lower 48 states. These interactions will ultimately determine the evolution of the upper level trough/shortwave in the Northwest next weekend. Agreement among model solutions has somewhat improved since the overnight forecast, now reflecting the most likely solution to be slower with less interaction with energy in Canada. The 06Z runs of the AI-GFS and EC-AIFS highlighted this trend and were even slower than the other deterministic solutions, though the 12Z AI-GFS is a bit too dramatic with this trend. The GFS runs have remained consistently too progressive, but the 12Z run showed a significant slow down and falls closer to the consensus. Ensemble means also showed a large spread of solutions, further highlighting the uncertainty surrounding the Northwestern trough evolution. Given good agreement, a near even blend of the deterministic guidance was used as a starting point for the forecast through the end of this week. Ensemble means from the ECENS and GEFS were added in increasing amounts through the weekend to help smooth out model differences, and the GFS was phased out since it was too progressive. This blend maintained continuity with the overnight forecast and the National Blend of Models. ...Weather/Hazards Highlights... The long duration heat wave is expected to linger over the Mid/Lower Mississippi Valley and southern Plains through much of the week with widespread Major to Extreme HeatRisk. Key Messages remain in effect with several record minimum and maximum temperatures in the forecast. The pattern becomes more uncertain by the weekend, but there is some trend for relief to northern areas, confining the greatest heat threat to the southern Plains. Above normal heat may also build briefly across the Southwest and parts of California mid-week as upper level ridging extends into the region. A low pressure system moving through eastern Canada will push a cold front across the Midwest and Northeast, which will trigger showers and thunderstorms from the Northeast and Mid-Atlantic to the Ohio and Mississippi Valleys Wednesday into Thursday. Locally heavy rainfall will be possible, especially in the Ohio Valley where the front will encounter an anomalously moist air mass and in the central Appalachians where terrain may enhance precipitation totals. This frontal boundary should move relatively quickly, which will help to limit flash flood potential. The focus for precipitation will shift to the Northwest late this week into next weekend as upper level troughing strengthens. This trough will push a cold front south across the Northwest and northern Plains late this week, which will bring unsettled weather to these regions. Early next week, the front will continue to move south across the Great Basin and Intermountain West while low pressure strengthens along the boundary over the northern/central Plains. Wintry weather will be possible in the northern Rockies next weekend as cooler air moves in behind the cold front, and heavy rainfall potential may develop over eastern Plains into the Upper Midwest ahead of the strengthening low early next week. Daily rounds of diurnal showers and thunderstorms are expected to continue in the Southeast and Southwest. A couple of weak frontal boundaries will move into the Southeast and dissipate, which will focus moisture and instability across the region. In the Southwest, monsoonal moisture will continue focus showers and thunderstorms in the Four Corners region. Dolan/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 $$