547 FXUS21 KWNC 231853 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 23 2026 SYNOPSIS: Model ensembles favor a continuation of extreme heat already under way across much of the persisting into week-2 tied to anomalous mid-level high pressure near the Four Corners increasing the chances of above-normal temperatures across southern Contiguous U.S. (CONUS), which when combined with Gulf moisture is likely to produce high heat indices east of the Rockies. Mid-level high pressure is favored to shift eastward and weaken early in the forecast period, slightly reducing the potential for extreme heat over the Desert Southwest. Antecedent dryness, combined with little precipitation favored over the next two weeks supports a Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and Lower Mississippi Valley and southern areas of the Middle Mississippi Valley. HAZARDS High risk of extreme heat for much of the Southern Plains and Lower Mississippi Valley and southern portions of the Central Plains and Middle Mississippi Valley, Mon-Tue, Aug 31-Sep 1. Moderate risk of extreme heat for the Southern Plains and Lower Mississippi Valley, Central Rockies, and Desert Southwest, as well as portions of the Central Rockies, Central Plains, Middle Mississippi Valley, Tennessee Valley, and Southeast U.S., Mon-Wed, Aug 31-Sep 2. Slight risk of extreme heat across the southern CONUS as well much of the Central Plains and Middle Mississippi Valley and portions of the Mid-Atlantic and California, Mon-Sat, Aug 31-Sep 5. Rapid Onset Drought (ROD) risk for much of the Southern Plains and Lower Mississippi Valley and adjacent portions of the Central Plains, Tennessee and Middle Mississippi Valleys, and Southeast U.S. DETAILED SUMMARY FOR WEDNESDAY AUGUST 26 - SUNDAY AUGUST 30: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR MONDAY AUGUST 31 - SUNDAY SEPTEMBER 06: Dynamical model guidance remains in good agreement regarding subtropical ridging persisting across the southwestern U.S. through week-2. The 0z ECMWF, GEFS, and Canadian ensembles depict a 594 dm 500-hPa height maximum at the start of the forecast period over the Four Corners region. Today's model solutions indicate a slight weakening, as well as a slight shift eastward of the ridge axis by the middle of week-2. Despite this weakening however, the synoptic pattern favors a continuation of a late summer heat wave across much of the southern half of the Lower 48. The potential for extreme heat is also well-indicated by a variety of forecast tools. The Probabilistic Extremes Tools (PETs) from the ECMWF and GEFS both indicate at least a 60% chance of maximum temperatures to exceed the 85th percentile at the outset of week-2, and a 40% chance of exceeding the same criteria into the middle of the forecast period. Daily computed heat indices above 100F are indicated across much of the south-central CONUS through the middle of the forecast period. As noted earlier, there are some indications of a weakening of the ridge during week-2 but despite this the signal for potential extreme heat remains robust. Therefore a high risk of extreme heat is maintained across much of the Southern Plains and Lower Mississippi Valley and surrounding regions, valid Aug 31-Sep 1. The high risk of extreme heat has been discontinued for the Desert Southwest but a moderate risk of extreme heat remains posted, valid Aug 31-Sep2 for the Desert Southwest, as well adjacent regions surrounding the high risk area highlighted above. Finally, a slight risk of extreme heat remains in place surrounding the moderate risk highlighted, as well as much of the Southeast U.S. and southern portions of the Mid-Atlantic, valid Aug 31-Sep 5. A Rapid Onset Drought (ROD) risk remains designated for much of the Southern Plains and Lower Mississippi Valley and adjacent portions of the Central Plains, Tennessee and Middle Mississippi Valleys, and Southeast U.S. This ROD area continues to register 30-day precipitation deficits greater than 2 inches, with little rainfall forecast during the next two weeks. Much of this ROD area is also included within the moderate risk of extreme heat as the potential for increased evapotranspiration rates also looks to reinforce this risk later in August. FORECASTER: Danny Barandiaran $$