457 FXUS21 KWNC 271837 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 27 2026 SYNOPSIS: Today's models are in better agreement compared to yesterday regarding mid-level ridging persisting across the south-central CONUS at least into the Labor Day Weekend. This favors a continuation of a stretch 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. Enhanced moisture advection favored over the southwestern CONUS increases chances for heavy precipitation across parts of the Desert Southwest. 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 Lower and Middle 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, Fri-Sun, Sep 4-6. Slight risk of extreme heat for parts of the Great Plains, Mississippi, Ohio, and Tennessee Valleys, Southeast, and Mid-Atlantic, Fri-Tue, Sep 4-8. Slight risk of much below normal temperatures for parts of the northern Great Basin, Northern Rockies, and Northern High Plains, Fri-Sat, Sep 4-5. Slight risk of heavy precipitation for parts of southern Arizona and southwestern New Mexico, Fri-Mon, Sep 4-7. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Lower and Middle Mississippi Valley. DETAILED SUMMARY FOR SUNDAY AUGUST 30 - THURSDAY SEPTEMBER 03: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR FRIDAY SEPTEMBER 04 - THURSDAY SEPTEMBER 10: While yesterday's ECMWF ensemble hinted at a potential break in the extreme heat across the central U.S., today's 0z ECMWF has jumped back to a more persistent mid-level ridge across the region, agreeing with the 0z GEFS. This favors anomalously warm temperatures (upwards of +10 deg F above normal) continuing across the Central and Southern Plains and adjacent areas of the Mississippi Valley through at least Labor Day Weekend. The GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict probabilities of 40-60 percent for maximum temperatures exceeding the 90th climatological percentile early in the period, with a very strong signal also being depicted in 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 is nudged slightly northward compared to yesterday and is now valid for Sep 4-6. While tools are marginally supportive of a high risk, it was not included due to the varying ECMWF guidance, as well as consideration of the 0z Canadian ensemble which continues to be more robust with troughing moving across the north-central CONUS and resultant decrease in heights across the Plains during week-2. The slight risk is now valid through Sep 8 and extends throughout much of the Midwest, and also into the Southeast and Mid-Atlantic. While positive 500-hPa height anomalies are forecast throughout the period, the declining temperature climatology and shortening daylight hours reduce confidence regarding extreme heat. 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 Lower Mississippi Valley, and is expanded farther north into the Middle 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 leads to increased onshore flow and moisture advection favoring above-normal precipitation over much of the West. 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, and 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 4-5. 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, with the National Hurricane Center (NHC) monitoring four separate areas of additional development in the next week. One area currently located near 135 deg E has a 90 percent chance of development (as of 11am PDT) where both ensembles and probabilistic tools show this potential system tracking westward to the south of Hawaii much in the same manner as Lala and Moke. 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 3-day precipitation values exceed the 85th climatological percentile across the state. Two other watch areas are being monitored closer to Mexico with high chances of development, with these disturbances tracking northwestward. As a result, there is some potential for a Gulf Surge event and moisture advention into the Desert Southwest. While tools are fairly weak with a heavy precipitation potential, there is still some support in the raw tools depicting increased precipitation amounts, and the PETs depict increased chances for 3-day amounts exceeding the 85th climatological percentile and a half-inch during the first half of week-2. Therefore, a slight risk of heavy precipitation is posted for portions of southern Arizona and New Mexico for Sep 4-7. Tropical Storm Dolly has formed across the Atlantic Main Development Region (near 40 deg W). However, NHC favors a weakening of this system as it approaches the Leeward Islands. Colder temperatures are also predicted for the Brooks Range in Northern Alaska during week-2. Though precipitation amounts are not expected to reach hazardous criteria, the region may experience its first snowfall of the season. FORECASTER: Thomas Collow $$