062 FXUS21 KWNC 221922 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 22 2026 SYNOPSIS: Models continue to favor a long-duration extreme heat event from the southern tier of the contiguous U.S. (CONUS) northward into the Central Plains and the Tennessee, Middle Mississippi, and Lower Ohio Valleys. The greatest risks are focused from the Desert Southwest into the Great Plains, Lower Mississippi Valley, and some adjacent areas under amplified and long-lived mid-level high pressure. Some areas may experience heat more typical of mid-summer into the first week of September. Meanwhile, unusually hot and dry conditions over the past few weeks are expected to continue through much of week-2, creating 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 much of the Desert Southwest, Southern Rockies, Southern and Central Plains, and Lower Mississippi Valley, Sun-Mon, Aug 30-31. Moderate risk of extreme heat for the Desert Southwest, Southern Rockies, Southern and Central Plains, Lower Mississippi Valley, and some adjacent areas, Sun-Tue, Aug 30-Sep 1. Slight risk of extreme heat for southern portions of California, the southern Great Basin, the Central and Southern Rockies, the Central and Southern Plains, the Middle and Lower Mississippi Valley, the Tennessee and Lower Ohio Valleys, the eastern Gulf Coast region, and southern portions of the Eastern Seaboard, Sun-Sat, Aug 30-Sep 5. Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains, the Lower Mississippi Valley and adjacent areas of the Middle Mississippi Valley. DETAILED SUMMARY FOR TUESDAY AUGUST 25 - SATURDAY AUGUST 29: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SUNDAY AUGUST 30 - SATURDAY SEPTEMBER 05: On day 8 (Aug 30), the 0z ECENS and 0z GEFS solutions predict a maximum mid-level height of 596-dm associated with the subtropical ridge near the Arizona-New Mexico border. The 0z CMCE solution depicts a regional height maximum of the same intensity, though displaced eastward over the Texas Panhandle. The GEFS and ECENS show standardized 500-hPa height anomalies topping out at 1.5-3.0 standard deviations above climatology on day 8. This is consistent with a long-duration, major heat wave over much of the central and southern CONUS through at least the first half of week-2, and perhaps well into early September in some areas. Concurrently, the 0z GEFS and 0z ECENS model runs forecast a mid-level trough off the West Coast, with the 588-dm height contour just north of San Francisco Bay. Over the course of week-2, the 588-dm contour is forecasted to shift southward to near Los Angeles by the end of the period, while the subtropical ridge weakens and shifts slightly eastward. The mid-level ridge is bookended by a pair of mean troughs over the eastern Pacific and over the northeastern CONUS. The National Blend of Models (NBM) depicts 8 stations with near-record or record-breaking daytime high temperatures scattered throughout the Southwest on day 8 (Aug 30), decreasing to 4 stations by day 10 (Sep 1). On day 8, Yuma is forecast to peak in the low 110's deg F, which ties the record set back in 1998. The NBM forecasts Tucson may reach 106 deg F on this same day, which is 1 deg F shy of the record set just 3 years ago in 2023. An even larger number of stations are predicted to experience near-record or record-breaking high minimum temperatures, which provides little in the way of overnight relief from the heat. According to the NWS historical Heat Risk tool, actual temperatures across the Central Valleys of California are predicted to range from about 99-100 deg F in the Sacramento Valley to 106-108 deg F in the southern San Joaquin and Tulare Valleys. The 105 deg F threshold was used as the cutoff between moderate (orange-level) and high (red-level) heat risk values. With a mid-level trough forecast to work its way southward across the state during the week-2 period, the northernmost extent of the slight risk of extreme heat in California was trimmed slightly compared to yesterday, now including just the Tulare and southern San Joaquin Valleys. Underneath the amplified ridge, a high risk of extreme heat remains posted early in week-2 (Sun-Mon, Aug 30-31) from the Desert Southwest eastward through the Lower Mississippi Valley, excepting some of the higher elevations in the Rockies. The ECENS Probability of Extremes Tools (PET) depicts a better than 60 percent chance for maximum temperatures to exceed the 85th historical percentile across the lower Four Corners region early in week-2, while the GEFS PET shows a stronger signal for more of week-2, as it has much of this summer, depicting better than 60 percent chances for daily highs to exceed the 85th percentile from the Four Corners region to the Southern Plains. Similar to yesterday, the high risk area for extreme heat is extended eastward from what the GEFS PET strictly indicates. This is due to the expectation that high dew points will elevate heat index values considerably above actual temperatures from the Lower Mississippi Valley eastward. The high risk area also covers a substantial portion of the Desert Southwest, where the ECENS and GEFS PETs start the period showing at least a 20 percent chance for temperatures to exceed 110 deg F. In fact, the 0z operational European model (ECMWF) and GFS model forecasts temperatures ranging from 115-120 deg F near the Salton Sea. A moderate risk of extreme heat is posted across a larger area surrounding the high risk area, and continues for one additional day (Sun-Tue, Aug 30-Sep 1). These time frames are consistent with most guidance derived from the GEFS and ECENS. Given the continuing model tendency to slow down deamplification and maintain more ridging with time near the end of week-2, a slight risk of extreme heat is extended for the duration of week-2 (through Sat Sep 5) across a large part of the central and southern CONUS. Temperatures in the Mid-Atlantic region are forecast to rise earlier in the period, then fall later in week-2, making for a difficult transition to predict. There is some support for a moderate risk of extreme heat east of the central Gulf Coast region, but models have not been consistent with themselves nor with each other in handling the mid-level trough stretching southward along the East Coast. This introduces considerable uncertainty in this region, precluding a moderate risk of extreme heat any farther east than the central Gulf Coast region. The episode of extreme heat is being exacerbated 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 with the possible exception of southern Louisiana. Nearly all of this ROD area is within the moderate and high risk areas of extreme heat, and the resulting increase in evapotranspiration rates are likely to accelerate surface moisture depletion. Tropical Storm Moke in the Central North Pacific is expected to pass south of Hawaii as a tropical storm during the next 1-3 days. The National Hurricane Center (NHC) is anticipating heavy rainfall in association with this system across portions of the state, likely exacerbating saturated ground conditions due to heavy precipitation from the passage of Hurricane Lala last week. The NHC is also following an area of disturbed weather much farther east (around 110W-115W as of 22 Aug), assessing an 80 percent chance of it becoming at least a tropical depression a week from now. There is a considerable amount of ensemble member spread in the forecast track of this feature, but there is the potential for this system to become the third tropical cyclone in a 3- to 4-week period to bring locally heavy to excessive rain and other impacts to the state. FORECASTER: Anthony Artusa $$