640 FXUS21 KWNC 281822 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 28 2026 SYNOPSIS: Broad mid-level ridging is forecast to persist across the southeastern and south-central contiguous U.S. (CONUS) into week-2 favoring a continuation of anomalous warmth and extreme heat centered across the Central and Southern Plains into the Middle and Lower Mississippi Valley. Mid-level low pressure forecast across the northwestern CONUS early in the period favors early season frosts or freezes, particularly across higher elevations. The abnormally hot and dry conditions over the past few weeks are expected to continue through much of week-2, supporting a Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley. HAZARDS Moderate risk of extreme heat for parts of the Central and Southern Plains, Middle and Lower Mississippi Valley, western portions of the Tennessee and Ohio Valleys, and the Southeast, Sat-Sun, Sep 5-6. Slight risk of extreme heat for parts of the Great Plains, Mississippi, Ohio, and Tennessee Valleys, Southeast, and Mid-Atlantic, Sat-Wed, Sep 5-9. Slight risk of much below normal temperatures for parts of the northern Great Basin, Northern Rockies, and Northern High Plains, Sat-Sun, Sep 5-6. 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 31 - FRIDAY SEPTEMBER 04: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY SEPTEMBER 05 - FRIDAY SEPTEMBER 11: The 0z ECMWF, GEFS, and Canadian ensembles are in good agreement regarding mid-level ridging across the south-central and southeastern CONUS at the start of week-2. However, the models indicate a decrease in amplitude of this feature compared to week-1 and an overall flattening of the ridge as it retrogrades slightly. This evolution supports a continuation of anomalously warm temperatures (upwards of +10 deg F above normal) continuing across the Central and Southern Plains and adjacent areas of the Mississippi Valley into Labor Day Weekend. The GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict at least a 40 percent chance of maximum temperatures exceeding the 90th climatological percentile early in the period, with a very strong signal also being depicted in the GEFS-ECMWF skill-weighted calibrated heat risk guidance. Actual temperatures in the upper 90s deg F to 100s deg F are likely with heat index values near 110 deg F in the more humid areas of eastern Texas and the Lower Mississippi Valley and 105 deg F farther north. As a result, the moderate risk for extreme heat remains posted Sep 5-6 across parts of the Central and Southern Plains, Middle and Lower Mississippi Valley, western portions of the Tennessee and Ohio Valleys, and the Southeast. The slight risk continues through Sep 9 and extends throughout much of the Midwest, and also into the Southeast and Mid-Atlantic. The slight risk is removed from most of the Florida Peninsula due to weaker signals in the heat risk guidance as well as the potential for an influx of tropical moisture tied to the remnants of Tropical Storm Dolly which may reduce temperatures. While positive 500-hPa height anomalies are forecast throughout the period, the declining temperature climatology and shortening daylight hours reduce confidence regarding extreme heat heading into mid-September. The continued extreme heat risks during week-2 are likely being reinforced by feedback processes associated with rapidly drying soils and drought within many of the highlighted regions. The hot and dry conditions favored are also expected to elevate the risk of fire weather conditions during the period. In addition, a Rapid Onset Drought (ROD) risk is designated across portions of the Central and Southern Plains and Middle and Lower Mississippi Valley. This area has registered 30- to 45-day precipitation deficits greater than 2 inches below normal and/or under half of normal, with less than an inch expected during the next two weeks. Amplified ridging forecast across the Gulf of Alaska results in downstream troughing developing over the northwestern CONUS. This favors enhanced onshore flow and moisture advection leading to above-normal precipitation over much of the West. The ECMWF and Canadian ensembles are quicker to weaken this feature early in week-2 compared to the GEFS, with a faster retrogression of the upstream ridge leading to rising heights over the West by day-10. While precipitation amounts are unlikely to reach hazards thresholds, cold air advection is forecast across portions of the Northwest, with both ECMWF and GEFS ensembles showing increased chances for nighttime minimum temperatures falling below 40 deg F (32 deg F in the higher elevations) supportive of the first frost and/or freezes. In addition, both GEFS and ECMWF PETs are in agreement indicating at least 20 percent chances of these temperatures falling below the 15th climatological percentile over some areas, thus a slight risk of much below normal temperatures is posted for parts of the northern Great Basin, Northern Rockies, and Northern High Plains for Sep 5-6. Even if any frost and/or freezes do not occur, the prospect of anomalously cold air is expected to alleviate fire weather conditions, as this part of the country has been embattled by ample wildfire activity this summer. Across the eastern and central Pacific, there has been a pronounced uptick in tropical activity during the past week. Tropical Storms Karina and Lowell are located near 115 deg W and 135 deg W respectively. The National Hurricane Center (NHC) forecasts Karina to strengthen into a major hurricane as it tracks west-northwestward. Karina along with a potential additional area highlighted with a high chance for tropical cyclone development in the same area may lead to enhanced moisture advection across the southwestern U.S. Both of these systems are forecast to be moving farther away from the U.S. by the start of week-2. However, the ECMWF ensembles depict another system potentially developing offshore Mexico with a similar track. While the slight risk of heavy precipitation is discontinued over the Desert Southwest in today's outlook, this potential third system will need to be monitored as it could trigger a renewed Gulf surge event in mid to late week-2. Tropical Storm Lowell is forecast to strengthen into a hurricane as it moves westward across the Pacific. This system will need to be monitored as some GEFS and ECMWF ensemble members turn the system more north toward the Hawaiian Islands early in week-2. Although there is ample uncertainty associated with this disturbance, heavy precipitation and other adverse impacts to Hawaii cannot be ruled out during week-2, with both the GEFS and ECMWF PETS depicting at least a 20 percent chance of 3-day precipitation values exceeding the 85th climatological percentile across the state. Across the Atlantic, Tropical Storm Dolly has opened up into a wave. There is some potential for regeneration if the remnants of this system make it into the western Atlantic where there is notably less wind shear. The timing and exact location are uncertain, but some individual GEFS and ECMWF ensemble members depict low pressure close to the southeastern U.S. coast early in week-2 which could have some implications for the extended outlook. Enhanced onshore flow may bring periods of heavy precipitation and gusty winds across southern Alaska late in week-1 into the start of week-2, although tools do not indicate hazards thresholds being reached. Snow cannot be ruled out across portions of the Brooks Range and the higher elevations of southeastern Alaska. FORECASTER: Thomas Collow $$