125 FXUS21 KWNC 121816 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 12 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 with enhanced chances for heavy precipitation extended into parts of the Northern and Central Plains and Upper Mississippi Valley. HAZARDS High risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi Valley, and Southeast, Thu-Fri, Aug 20-21. Moderate risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi and Tennessee Valleys, and Southeast, Thu-Sun, Aug 20-23. Slight risk of extreme heat for portions of the Central and Southern Plains, Mississippi, Ohio, and Tennessee Valleys, Southeast, and southern Mid-Atlantic, Thu-Wed, Aug 20-26. Slight risk of heavy precipitation for portions of the Four Corners, Northern and Central Plains, and the Upper Mississippi Valley, Thu-Sat, Aug 20-22. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley. DETAILED SUMMARY FOR SATURDAY AUGUST 15 - WEDNESDAY AUGUST 19: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY AUGUST 20 - WEDNESDAY AUGUST 26: 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 over the Southeast, Lower Mississippi Valley, and Southern Plains through the middle of the period before slowly deamplifying. As a result, confidence remains high for a continuation of the long duration heat event through the middle of week-2. By the end of week-2, the mid-level pattern becomes more uncertain with weaker anomalies. This may just be a function of increased spread among the ensemble guidance and continuation of the heat into week-3 remains possible. 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. 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. 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. A high risk of extreme heat is forecast for the Central and Southern Plains, Lower Mississippi Valley, and the Southeast, where heat index values may exceed 110 deg F, and is valid Aug 20-21. The strongest signal is reduced over the southern Atlantic states and the high risk is correspondingly pulled back from South Carolina and Georgia. The moderate risk for extreme heat is valid for an additional day relative to prior forecasts, through Aug 23, and extends into the Central Plains and Middle Mississippi Valley where there is increased potential for heat index values to exceed 105 deg F. A slight risk, for all of week-2, surrounds the moderate risk area and continues extends into the Upper Mississippi Valley where some tools are suggesting at least a brief chance of extreme heat. 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. Most of the guidance suggests a reduction in the chances for heavy precipitation across the Four Corners by the middle of week-2. However, some physical and machine learning guidance favors elevated chances for heavy precipitation into portions of the Plains and Mississippi Valley. Therefore, the slight risk is expanded towards the Great Lakes region from the Southwest. Most tools suggest the heavy precipitation risk times off by the middle of week-2. Therefore, a slight risk of heavy precipitation is posted for portions of the Desert Southwest, Great Basin, the Southern and Central Rockies, Central and Northern Plains, and Upper Mississippi Valley, valid Aug 20-22. 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 western Canada tied to the weakening of the mid-level ridge over the southeastern U.S. At this time, tools do not favor elevated extreme heat chances over the West but will be monitored. 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: Ryan Bolt $$