700 FXUS21 KWNC 161807 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 16 2026 SYNOPSIS: A major, long duration period of extreme heat is expected to persist into week-2 across the central CONUS and a large part of the Nation's southern tier. Models converge most strongly on the Red River (South) Valley, most of Oklahoma, and some adjacent areas early in the period, where a high risk for extreme heat is posted. At least a slight risk of extreme heat covers most of the southern tier of the Nation from the Desert Southwest to the South Atlantic Coast. Anomalous mid-level high pressure near the Four Corners is forecast in concert with an incursion of Gulf moisture, producing high heat index values. This mid-level high pressure is favored to drift slowly westward or southwestward while deamplifying, ending the extreme heat risk late week-2. Meanwhile, given antecedent dryness, the above-normal temperatures and subnormal rainfall expected for next two weeks support a Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and Middle and Lower Mississippi Valley. HAZARDS High risk of extreme heat for the Red River (South) Valley, much of Oklahoma, and some adjacent areas, Mon-Tue, Aug 24-25. Moderate risk of extreme heat for much of the Central and Southern Plains, parts of the Lower Mississippi and Tennessee Valleys, and adjacent Southeast, Mon-Wed, Aug 24-26. Slight risk of extreme heat for portions of the Southwest, Southern Rockies, Central and Southern Plains, Lower Mississippi and Tennessee Valleys, and Southeastern CONUS, Mon-Fri, Aug 24-28. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley. DETAILED SUMMARY FOR WEDNESDAY AUGUST 19 - SUNDAY AUGUST 23: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR MONDAY AUGUST 24 - SUNDAY AUGUST 30: Dynamical models remain in good agreement regarding subtropical ridging across the south-central to southwestern U.S. through most of week-2. The 0z European ensemble (ECENS), GEFS, and Canadian ensemble (CMCE) means all start the period with a 596 dm 500-hPa height maximum centered near the south-central CONUS or eastern Four Corners region. The ECENS and GEFS are in excellent agreement placing the center of this feature over northern or eastern New Mexico while the CMCE mean depicts this feature over the Red River (South) Valley, but the slightly farther west placement is favored since it is the majority solution, and more consistent with earlier runs. Meanwhile, ensemble means depict a somewhat stronger and more persistent mid-level trough over the northeastern CONUS relative to yesterday. The CMCE mean is strongest with this feature and the ECENS mean the weakest, with the GEFS mean splitting the difference. The GEFS mean, which approximately equals the average of all three ensemble means, is favored with this mid-level trough. Over the course of week-2, the 500-hPa height center remains roughly in place over the central and southwestern CONUS while slowly flattening and deamplifying. Today's model consensus shows this process happening more slowly than depicted yesterday, and also starts the period with a slightly more amplified mid-level ridge. As a result, the forecast of a long-duration heat event is maintained. The longer-lived and more-amplified mid-level ridge depicted today, along with good agreement among the Probabilistic Extremes Tools (PETs), prompted posting a high risk of extreme heat where model guidance converges most strongly, namely the Red River (South) Valley, much of Oklahoma, and some adjacent areas early week-2 (Mon-Tue Aug 24-25). The moderate risk of extreme heat is longer-lasting and slightly more expansive than yesterday, covering the southern halves of the Plains and Mississippi Valley, the Tennessee Valley, and the adjacent Southeast. After shifting westward yesterday, the ensemble means support a shift back toward the east today. This is especially true in the European ensemble (ECENS) mean, which lets the center of the 500-hPa ridge drift eastward into the southern Plains before it weakens and sinks toward the Mexico/New Mexico Border. The Canadian ensemble (CMCE) and the GEFS maintain the center of the mid-level ridge farther west, consistent with yesterday's GEFS and ECENS mean. Since the GEFS mean has been most consistent over the past few runs, and because it is the majority solution, the official forecast favors less of a jog to the east than forecast by the ECENS mean, but it has moved slightly in that direction. This scenario supports expanding the slight risk area farther up the East Coast than yesterday, through most of Georgia and South Carolina. The slight risk is removed after Fri Aug 28, in concert with the deteriorating mid-level ridge. Both the GEFS and ECENS PETs depict at a 40 to 70 percent chance of maximum temperatures exceeding the 85th climatological percentile early week-2 over the Red River (South) Valley, Oklahoma, and some adjacent areas. This coincides with the posted high risk of extreme heat, and is slightly more robust in the ECENS PET than yesterday. The PETs show progressively decreasing odds for extreme heat with time, but the ECENS PET keeps higher chances for extreme heat farther east after the first day of the period. Again, the GEFS PET is favored, but some credence has been given to the ECENS since it resembles the consensus from a couple days ago. Increased humidity is expected to contribute to extreme heat index values from the Southern Plains eastward, with a strong signal in the calibrated skill-weighted GEFS-ECMWF heat risk guidance, particularly across the Lower Mississippi Valley and parts of the Southeast, where the heat index may exceed the actual temperature by 10 deg F or more, according to internal heat index guidance from both the GEFS and ECENS. Probabilities for heat index values to top out at 105 deg F or higher exceed 70 percent in parts of this region, and the chances for maximum heat index values over 110 deg F exceed 50 percent in South Texas and the Lower Colorado Valley, and ranges from 20 to 40 percent across Oklahoma, southernmost Kansas, Louisiana, Mississippi, Arkansas, northern Texas, and some areas near the Gulf Coast. In addition, the National Blend of Models (NBM) depicts nighttime lows nearing or breaking daily records early week-2 from southern Florida to southern California, resulting in little overnight relief from daytime 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 over the Four Corners, especially the higher elevations of Colorado. Confidence in a healthy monsoon remains high, but conditions do not appear robust enough to reach hazards thresholds, so no hazards are posted. Still, isolated areas of heavy rain remain possible, and this region is prone to flash flooding even with relatively low rainfall totals along dry creek beds (arroyos) and in canyons. Caution should always be exercised in such areas if thunderstorm activity is initiated nearby. Also, some convective activity may result in little or no rainfall while still being capable of generating lightning, which poses a risk of wildfire initiation. 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 (near or under half of normal), with little rainfall expected during the next two weeks. Furthermore, much of this ROD area is within the moderate risk of extreme heat. This could potentially increase evapotranspiration rates and accelerate surface moisture depletion. FORECASTER: Rich Tinker $$