979 FXUS21 KWNC 261822 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 26 2026 SYNOPSIS: A lingering area of mid-level high pressure over the southern tier of the contiguous U.S. (CONUS) supports a continued risk of excessive heat, with the greatest risk focused over the Southern Plains and Lower Mississippi Valley early in the period. Tied to a strengthening area of mid-level high pressure over the northeastern Pacific, there is growing support for strong cold air advection to bring much below normal temperatures over parts of the northwestern CONUS. Enhanced moisture advection favored over the southwestern CONUS towards the later part of next week 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 Middle and Lower Mississippi Valley. HAZARDS Moderate risk of extreme heat for parts of the Southern and Central Plains, Lower and Middle Mississippi Valley, western portions of the Tennessee and Ohio Valleys, and the Southeast, Thu, Sep 3. Slight risk of extreme heat for parts of the Great Plains, Mississippi, Ohio, and Tennessee Valleys, Southeast, and Mid-Atlantic, Thu-Sun, Sep 3-6. Slight risk of much below normal temperatures for parts of the northern Great Basin, Northern Rockies, and Northern High Plains, Thu-Sat, Sep 3-5. Slight risk of heavy precipitation for parts of southern Arizona and southwestern New Mexico, Sat-Mon, Sep 5-7. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains, the Lower Mississippi Valley and adjacent areas. DETAILED SUMMARY FOR SATURDAY AUGUST 29 - WEDNESDAY SEPTEMBER 02: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY SEPTEMBER 03 - WEDNESDAY SEPTEMBER 09: Over the past week or so, dynamical models have been consistent in favoring a fairly stable 500-hPa height pattern, with the main height features consisting of enhanced subtropical ridging over the Southern Tier of the CONUS with an anomalous ridge axis extending northward into Canada, bookended by a pair of mean troughs over the northwestern and northeastern CONUS. However, since yesterday, both the GEFS and ECMWF have fallen more out of phase with one another. While both models are in agreement in amplifying a secondary amplified ridge center over the northeastern Pacific, the ECMWF is more progressive with a mean trough being forced downstream, which erodes much of above-normal heights that have persisted throughout the western and central CONUS, while also shifting the ridge axis into the eastern CONUS towards the middle of the period. The GEFS, on the other hand, favors a much more stable pattern, maintaining the mean troughing established over the northwestern and northeastern CONUS, with some suppression of the enhanced subtropical ridging over the Southern Tier of the U.S. As a result of these discrepancies, there is increased uncertainty in the updated hazard outlook, particularly by the middle of the period, with implications on the duration of a long lived heat event that has affected much of the southern U.S. for much of August. Based on declining support in the temperature tools with much of the hottest temperatures timing off, the high risk of extreme heat is discontinued in the updated outlook. However, a moderate risk of extreme remains issued for day 8 (Sep 3), where both the GEFS and ECMWF Probabisitic Extreme Tools (PETs) agree in featuring at least 30% chances for daytime temperatures exceeding the 90th percentile, along with continued support in the calibrated heat tools indicating elevated chances for heat index values reaching the 90th percentile. Based on the eastward expansion of signals in percentile space in these tools, the moderate risk area is adjusted to include portions of the Tennessee and Ohio Valleys and the Southeast, with coverage removed over the Southern High Plains associated with cooler temperatures being favored. Within the highlighted moderate risk area, there continues to be good model support for double digit temperature anomalies, translating to daytime temperatures likely exceeding 95 and 100 deg F in many locations, with heat index values reaching 110 deg F where higher dewpoints are expected across parts of southern Texas and the Lower Mississippi Valley. Surrounding the moderate risk area, a slight risk of extreme heat remains posted for much of the south-central and southeastern CONUS through Sep 6. With more troughing over the West Coast, coverage of the slight risk is removed over much of the Desert Southwest, and is no longer valid for the entirety of week-2 due to the aforementioned model differences associated with how the troughing evolves from the West. In the absence of exceptionally strong subtropical ridging in early September (ensembles maintain low chances for heights exceeding 594 dm by day 11), chances for extreme heat being realized are reduced given shortening daylight hours, even in the lower latitudes. 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 (and parts of 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. The amplifying ridge over the northeastern Pacific also introduces the potential for stronger cold air advection into the northwestern CONUS early in week-2. Both ECMWF and GEFS ensembles show 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% 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 3-5. 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, where the National Hurricane Center (NHC) is currently eyeing two active Tropical Cyclones (Lala and Iselle), along with four watch areas for development in the Tropical Weather Outlook (TWO). One watch area currently located near 135E has 70% chances 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. Two other watch areas in the TWO are located closer to Mexico, and regardless of formation during the next week, a low tracking near the Gulf of California may trigger a surge event and bring enhanced moisture into the Desert Southwest. While tools are fairly tenuous with a heavy precipitation potential, there is still some support in the raw tools depicting increased precipitation amounts, and calibrated PETs show a northward expanding area with increased chances for 3-day amounts exceeding the 85th percentile during the middle of week-2. Therefore, a slight risk of heavy precipitation is posted for portions of southern Arizona and New Mexico for Sep 5-7. Elsewhere, ensembles point to marginal heavy precipitation risks over parts of the Midwest and along parts of the northern eastern Seaboard early in the period, however neither the GEFS and ECMWF PETs are in agreement in these regions, precluding any corresponding hazards. 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: Nick Novella $$