035 FXUS02 KWBC 200736 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 336 AM EDT Thu Aug 20 2026 Valid 12Z Sun Aug 23 2026 - 12Z Thu Aug 27 2026 ...Hazardous heat will continue across the Southern Plains and Lower Mississippi Valley... ...Overview... A strong and persistent upper high will maintain hazardous heat across the southern tier through next week, particularly across the Southern Plains and Lower Mississippi Valley. Monsoonal moisture is forecast to stream north under the ridge for scattered convection across the Intermountain West and Rockies, while rounds of rain dive through portions of the central U.S. as well. Meanwhile, multiple shortwaves should maintain troughing in the East. Rain is likely for the Northeast early next week as a first low pulls away, and then rain and thunderstorms are forecast to overspread parts of the eastern U.S. again Tuesday and Wednesday. ...Guidance/Predictability Assessment... Model guidance remains agreeable on a fairly stagnant pattern, with the anchoring upper high and troughing in the East. Dynamical/AI models are showing relatively good agreement with a closed upper low center near the Great Lakes and adjacent Canada Sunday-Monday, with some minor surface low position differences. Upstream, a potent shortwave will round the northern side of the ridge, tracking across southern Canada early in the week. This shortwave looks to dive southeast into the Midwest/Great Lakes by midweek, potentially serving to deepen the trough in the East. However, models are variable with its evolution, as there are remaining questions with energy diving south through Canada that could interact with it. So the details of the eastern trough are uncertain especially by Wednesday-Thursday. Meanwhile, a trough/low is forecast to dive from the northeastern Pacific and track near the Pacific Northwest by midweek. 00Z model guidance is even more variable with the timing of this feature moving east compared to the previous cycle. The ECMWF/CMC now spin the low farther west/well offshore, while the GFS takes it inland quickly through British Columbia. The 00Z EC-AIFS seems to be a good middle ground with the timing, while the 00Z AIGFS is similar to the GFS. So will not favor the very slow EC/CMC unless the AI models trend that way too. The WPC forecast used a multi-model blend of the dynamical and AI guidance early in the forecast period, and increased the proportion of the ensemble means as the period progressed and model spread increased. ...Weather/Hazards Highlights... Hot temperatures well into the 100s, with oppressive heat indices, are forecast across the south-central U.S. into 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. Farther west, highs near and above 110 in the Desert Southwest could also cause heat concerns next week. Areas of the Southeast may reach a few degrees above normal at times with moist dewpoints. See WPC's Key Messages for more on the extreme heat. Elsewhere, most areas will be close to average for temperatures, with the Ohio Valley and vicinity a bit below average early in the week under upper troughing. An upper/surface low in southeast Canada pulling away will bring rain chances to the Northeast on Sunday, potentially lasting across the Interior Northeast for Monday-Tuesday. Through the period, monsoonal moisture is forecast to bring scattered, diurnally driven showers and thunderstorms to the Intermountain West/Rockies. Isolated flash flooding is possible especially across sensitive areas like burn scars, favored terrain like slot canyons, and urban areas. 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 rainfall positions and amounts are uncertain, but generally the northern/central Plains and the Mississippi Valley could be impacted early in the week. Rain chances are forecast to push into the Midwest/Great Lakes and Southeast Tuesday and could overspread much of the Eastern Seaboard by midweek. 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 $$