776 FXUS21 KWNC 111809 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 11 2026 SYNOPSIS: A major, long duration period of extreme heat continues to be predicted across portions of the south-central contiguous U.S. (CONUS) and Southeast persisting into week-2 tied to anomalous mid-level high pressure combined with high humidity levels. Model guidance has continued to support a very strong heat event across the south-central and southeastern CONUS. 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 Middle and Lower Mississippi Valley. Enhanced monsoonal activity continues to be indicated across the Four Corners, although with less certainty with downstream progression across the Midwest as some of the stronger signals have now shifted into week-1. HAZARDS High risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi Valley, and Southeast, Wed-Fri, Aug 19-21. Moderate risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi and Tennessee Valleys, Southeast, and southern Mid-Atlantic, Wed-Sat, Aug 19-22. Slight risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi and Tennessee Valleys, Southeast, and southern Mid-Atlantic, Wed-Tue, Aug 19-25. Slight risk of heavy precipitation for portions of the Four Corners, Wed-Sun, Aug 19-23. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley. DETAILED SUMMARY FOR FRIDAY AUGUST 14 - TUESDAY AUGUST 18: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY AUGUST 19 - TUESDAY AUGUST 25: Dynamical model guidance remains in good agreement regarding subtropical ridging persisting across the south-central and southeastern U.S. into week-2. The 0z ECMWF, GEFS, and Canadian ensembles depict a 594-596 dm 500-hPa height maximum slowly retrograding from the Southeast to the Southern Plains throughout the period, with its amplitude steady or even increasing slightly. As a result, confidence remains high for a long duration heat event, with many tools indicating the potential for oppressive conditions lingering well into late August. Both the GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict at least a 60 percent chance of maximum temperatures exceeding the 85th climatological percentile at the start of week-2 centered across the Central Gulf Coast states, and remaining above 40 percent through the middle of week-2. The ECMWF and GEFS both continue to indicate a retrogression of the ridge axis during week-2, although the GEFS is more bullish in this scenario than the ECMWF, which was more aggressive yesterday. These discrepancies are minor though and in sum the forecast confidence remains high with a consistent trend in model guidance. A large contribution from increased humidity is expected, with a strong signal in the calibrated skill-weighted GEFS-ECMWF heat risk guidance, particularly across the Central and Southern Plains and adjacent Mississippi Valley where probabilities exceed 60 percent for maximum heat index values to exceed the 95th climatological percentile. A high risk of extreme heat is forecast for the Central Plains, Middle Mississippi Valley, and the Southeast, where heat index values may exceed 110 deg F, and is valid Aug 19-21. In addition, the National Blend of Models (NBM) also depicts a number of locations with nighttime lows nearing and/or breaking daily records, resulting in little overnight relief from the daytime heat. The moderate risk for extreme heat remains valid through Aug 22 and continues to extend into the Central Plains where there is increased potential for heat index values to exceed 105 deg F. A slight risk surrounds the moderate risk area and continues for all of week-2. Troughing initially near the West Coast of the CONUS favors an influx of moisture across much of the western U.S., and enhanced Southwest Monsoon activity continuing over the Four Corners where the GEFS and ECMWF PETs depict at least a 20 percent chance 3-day precipitation exceeds the 85th climatological percentile and a half-inch early in week-2. The ECMWF maintains this signal through the forecast period, while the GEFS drops below these thresholds by midweek. With model solutions generally indicating a weakening of troughing along the West Coast a gradual reduction in monsoon activity seems more likely. Therefore, a slight risk of heavy precipitation is posted for portions of the Desert Southwest, Great Basin, and the Southern and Central Rockies, valid Aug 19-23. This region is prone to flash flooding even with relatively small precipitation accumulations especially along dry creek beds (arroyos) and in canyons. Caution should always be exercised in such areas should thunderstorm activity initiate nearby. Toward the middle of week-2, troughing along the West Coast is favored to retreat with rising heights across the West tied to expansion of the ridging over the south-central CONUS. This evolution would decrease the moisture advection into the West, and also promote an increase in above-normal temperatures and possibly extreme heat across portions of the Interior West where the GEFS PET depicts increasing coverage of probabilities greater than 20 percent for maximum temperatures to exceed the 85th climatological percentile. However, due to lower probabilities in the ECMWF PET, no related extreme heat hazards are posted across the West at this time. A Rapid Onset Drought (ROD) risk remains designated across portions of the Central and Southern Plains and Middle and Lower Mississippi Valley. 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 $$