789 FXUS21 KWNC 251835 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 25 2026 SYNOPSIS: A persistent area of strong mid-level high pressure over the southern tier of the contiguous U.S. (CONUS) supports above-normal late summertime temperatures and a continued risk of excessive heat, with the greatest risk focused over the Southern Plains early in the period before mid-level high pressure gradually eases with time. 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 High risk of extreme heat for the Central and Southern Plains, and portions of the Lower and Middle Mississippi Valley, Wed, Sep 2. Moderate risk of extreme heat for the parts of the Desert Southwest, Southern and Central Plains, Lower and Middle Mississippi Valley, and some adjacent areas, Wed-Thu, Sep 2-3. Slight risk of extreme heat for southern parts of California, the southern Great Basin, Rockies, Great Plains, Mississippi, Tennessee, and Lower Ohio Valleys, eastern Gulf Coast region, and southern portions of the Eastern Seaboard, Wed-Tue, Sep 2-8. Slight risk of heavy precipitation for parts of southern Arizona and southern New Mexico, Fri-Sun, Sep 4-6. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains, the Lower Mississippi Valley and adjacent areas. DETAILED SUMMARY FOR FRIDAY AUGUST 28 - TUESDAY SEPTEMBER 01: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY SEPTEMBER 02 - TUESDAY SEPTEMBER 08: Over the past week or so, dynamical models continue to favor a fairly stable 500-hPa height pattern for the week-2 period. The main mean height features consist of enhanced subtropical ridging overspreading the southern tier of the U.S. with an anomalous ridge axis extending northward into Canada, bookended by a pair of mean troughs over the northwestern and northeastern CONUS, all of which are favored to persist into early September. Accompanying the strong subtropical ridging, there continues to be good support for the continuation of a long duration late summer heat wave, though both the GEFS and ECMWF ensembles have become slightly less amplified with this height feature over the past several days, resulting in a slightly decreased risk of extreme heat in the updated outlook. While the subtropical ridge center has been shown to meander, shifting zonally between the lower Four Corners and the Lower Mississippi Valley since last week, models are in agreement with the position and strength of the ridge center over the Southern High Plains by the outset of the period, where the greatest risk of extreme heat is expected to be initially focused. Over time, there are lowering chances for 500-hPa heights exceeding 594 dm ridge center, with a large dispersion of weak height exceedance signals throughout the southern tier of the U.S.. As a result, there is more uncertainty as to where the ridge center will migrate next, and whether the heat event will persist into and beyond Labor Day weekend. Underneath the subtropical ridge center, a high risk of extreme heat is posted with coverage now limited from eastern New Mexico eastward into portions of Oklahoma and Texas, and adjacent parts of the Central Plains and Mississippi Valley. This high risk is supported by calibrated heat tools indicating elevated chances (>50%) for daytime temperatures and/or heat index values exceeding the 90th climatological percentile, elevated maximum temperature signals in percentile space among the Probabisitic Extreme Tools (PETs), and the National Blend of Models showing a number of locations with daytime highs nearing and/or breaking daily records over the Southern High Plains. The high risk remains valid through Sep 2 before the same NBM analysis shows a reduction to zero locations, which is also supported by 24-hour temperature changes in the ECMWF and GEFS ensembles depicting a slight daytime cooling trend over the highlighted high risk area by the middle of next week. Within the highlighted high risk area, daytime temperatures are likely to exceed 100 deg F in many locations (except for the higher elevations), with heat index values possibly exceeding 110 deg where dewpoint temperatures are higher. Surrounding the high risk area, a moderate risk of extreme heat remains posted where temperature and heat tools maintain lesser, but increased chances for temperatures exceeding the upper climatological percentiles through Sep 3. Coverage of the moderate risk area is removed over the Desert Southwest, and along the Rio Grande Valley and Gulf Coast based on cooler temperatures favored in the region and where there is less support for positive temperature anomalies exceeding 5 deg F in the raw model tools. A broad slight risk area of extreme heat remains posted across the southern tier of the U.S, with coverage added over parts of the Tennessee and Ohio Valleys and Mid-Atlantic based on an uptick in temperature signals in the latest tools early in the period. While the mid-level pattern looks to become more zonal late in week-2, the slight risk remains valid for the entirety of week-2 due to PETs maintaining increased chances for maximum temperatures exceeding the 85th percentile for much of the southern tier. The persistent, elevated chances for extreme heat is 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. Across the eastern and central Pacific, there has been pronounced uptick in tropical activity during the past week, where the National Hurricane Center (NHC) is currently eyeing tree active Tropical Cyclones (Lala, Iselle, and Julio), 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. While 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. With troughing also favored to persist over the West Coast to help pull moisture into the southwestern CONUS early in week-2, the ECMWF ensemble favors an increase in anomalous precipitable water reflective of enhanced moisture advection favorable for locally heavy precipitation. While tools are fairly tenuous with a heavy precipitation potential, there is growing support in the raw and calibrated ECMWF PET towards the middle of week-2 with increased chances for 3-day amounts exceeding the 85th percentile. Therefore, a slight risk of heavy precipitation is posted for portions of southern Arizona and New Mexico for Sep 4-6. Episodes of high winds are also possible at the base and ahead of the trough axis across portions of the West Coast. However, no corresponding high wind hazards are issued due to the deamplification of the troughing by the middle of next week, and a lack of support in the tools. Colder temperatures are 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 $$