210 FXUS21 KWNC 141821 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 14 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 near the Four Corners combined with Gulf moisture to produce high heat indices. Mid-level high pressure is favored to spread westward, increasing the risk for extreme heat in 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 Middle and Lower Mississippi Valley. HAZARDS Moderate risk of extreme heat for portions of the Southern Plains, Lower Mississippi and Tennessee Valleys, and Southeastern U.S., Sat-Sun, Aug 22-23. Slight risk of extreme heat for portions of the Central and Southern Plains, Middle and Lower Mississippi and Tennessee Valleys, and Southeastern U.S., Sat-Thu, Aug 22-27. Slight risk of extreme heat for portions of the Desert Southwest, Sat-Wed, Aug 22-26. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley. DETAILED SUMMARY FOR MONDAY AUGUST 17 - FRIDAY AUGUST 21: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY AUGUST 22 - FRIDAY AUGUST 28: 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 594-596 dm 500-hPa height maximum retrograding into the Intermountain West early in 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 40 percent chance of maximum temperatures exceeding the 85th climatological percentile through the middle of week-2 centered across the Central Gulf Coast states. The ECMWF and GEFS continue to depict a ridge retrogression, now mostly in week-1, with the ridge axis established over the Four Corners by the start 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 some locations. 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 moderate risk for extreme heat remains valid through Aug 23 and continues to extend into the Southern Plains where there is increased potential for heat index values to exceed 105 deg F. A slight risk surrounds the moderate risk area and covers Aug 22-27. 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. However over the last several days a reduction in signal strength has been noted. With model solutions generally indicating a weakening of troughing along the West Coast, a gradual reduction in monsoon activity seems increasingly likely. Therefore the slight risk of heavy precipitation from yesterday’s outlook has been discontinued. However, isolated areas of heavy rain remain possible and 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. Finally, as monsoon moisture declines, any continued convective activity may result in relatively little rainfall while still being capable of generating lightning, which can pose a risk of wildfire initiation. 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. Daily maximum temperatures from multiple model ensembles exceed 105F across the Sonoran and Mojave deserts through the middle of week-2, after which indicated maximum temperatures moderate somewhat. Increased humidity from the monsoon is likely to result in relatively muggy conditions for the area. Therefore a slight risk of extreme heat is posted for much of the Desert Southwest and extending into central New Mexico, valid Aug 22-26. 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 $$