149 FXUS02 KWBC 190733 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 AM EDT Wed Aug 19 2026 Valid 12Z Sat Aug 22 2026 - 12Z Wed Aug 26 2026 ...Hazardous heat will continue across the southern Plains and Lower Mississippi Valley... ...Overview... A strong and persistent upper high will be in place over the Four Corners states to southern/central Plains this weekend into next week, maintaining hazardous heat that will last the longest across the southern Plains and Lower Mississippi Valley. Monsoonal moisture is forecast to stream north under the ridge for scattered convection across the West, while rounds of rain dive through portions of the central U.S. as well. Meanwhile, multiple shortwaves should maintain troughing in the East, leading to rain and thunderstorms across the Eastern Seaboard into the weekend. ...Guidance/Predictability Assessment... Model guidance remains agreeable on a fairly stagnant pattern, with the anchoring upper high and troughing in the East. The multiple shortwaves within the trough and its evolution/depth from day to day are less certain. Most dynamical/AI models are showing relatively good agreement with a closed upper low center near the Great Lakes and adjacent Canada Sunday-Monday, though the GFS (including the new 00Z run) is farther north and more progressive. Upstream, AI and dynamical model guidance agree on a shortwave moving from the eastern Pacific into the Northwest Saturday, but timing differences remain a challenge. GFS runs including the 00Z as still a bit faster than consensus as the shortwave moves quickly across southern Canada Sunday-Monday and toward the Upper Midwest Tuesday. This shortwave could serve to deepen the trough in the East again by midweek as it dives into the Midwest/Great Lakes, after the trough becomes shallower Monday-Tuesday. The 00Z GFS even creates a closed low over the Upper Great Lakes from this feature, which seems possible, but it is stronger than other models. Then a trough/low is forecast to dive from the northeastern Pacific nearing the Pacific Northwest for midweek. Models are agreeable with this, except for the CMC (12Z and 00Z), which shows a much faster track across Canada and the U.S. northern tier than consensus, becoming out of phase with central North American troughing where other models have ridging by Wednesday. Thus, the WPC forecast used a multi-model blend early in the period, and then leaned away from the GFS and CMC in favor of the ECMWF, AIFS/AIGFS, and increasing proportions of the ensemble means. ...Weather/Hazards Highlights... Hot temperatures well into the 100s, with oppressive heat indices, are forecast across the south-central U.S. for the weekend and into much of next week under the strong upper high. Record-breaking warm overnight temperatures across the southern tier will further limit recovery from the heat, especially since several consecutive days of heat will occur. Widespread Major to Extreme HeatRisk will persist in the southern Plains and Lower Mississippi Valley. Several consecutive days of high heat stress can lead to heat- related illnesses. The West should also see warm to hot temperatures primarily Saturday when the upper ridge reaches the farthest north. The Southeast should see some minor relief over the weekend as the trough aloft and weak cold fronts lessen the magnitude and scope of the heat, but could gradually warm again as next week progresses. Over the weekend, combining energies and frontal systems will allow for widespread rain and thunderstorms across the East. Rain amounts should generally stay light to moderate, but some heavier amounts are possible in coastal areas of the Mid-Atlantic Saturday, with isolated flash flooding possible. By Sunday rain chances are forecast to focus in the Great Lakes/Appalachians/Northeast as the surface low/frontal systems move through, and some could linger Monday for the Interior Northeast on the backside of the low. Scattered showers and thunderstorms remain possible for Florida through the period. Monsoonal moisture is forecast to bring scattered, diurnally driven showers and thunderstorms to the Intermountain West through the period. Localized flash flooding is possible especially across sensitive areas like burn scars, favored terrain like slot canyons, and urban areas. A round of rain is also possible with a shortwave in the Pacific Northwest and into the northern Rockies, likely peaking Saturday. Areas of rain and storms are also possible in the central U.S. as shortwaves round the northeast side of the ridge and dive southeast. Placement of these shortwaves and thus the rain chances are uncertain, but generally the northern/central Plains and the Mississippi Valley could be impacted, reaching the Southeast into the workweek. Tate 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 $$