405 FXUS21 KWNC 081754 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT August 08 2026 SYNOPSIS: Mid-level high pressure is forecast across the south-central and southeastern contiguous U.S. (CONUS) during week-2 favoring a persistence of the extreme heat risk over these areas. Antecedent dryness, combined with little precipitation favored over the next two weeks supports a Rapid Onset Drought (ROD) risk for portions of the Southern and Central Plains and Lower Mississippi Valley. A weak but broad area of mid-level low pressure across eastern Canada favors enhanced northwesterly mid-level flow and relatively cooler weather across the northeastern CONUS. This set-up also favors a progression of enhanced moisture and frontal activity from the Four Corners to the Midwest and Eastern Seaboard where periodic heavy precipitation is possible early in week-2. HAZARDS Moderate risk of extreme heat for portions of the Southern Plains, Lower Mississippi Valley, and Southeast, Sun-Tue, Aug 16-18. Slight risk of extreme heat for much of the south-central and southeastern CONUS, Sun-Sat, Aug 16-22. Slight risk of heavy precipitation for portions of the Four Corners, Northern and Central Plains, Midwest, Tennessee Valley, Northeast, and Mid-Atlantic, Sun-Tue, Aug 16-18. Rapid Onset Drought (ROD) risk for portions of the Southern and Central Plains and the Lower Mississippi Valley. DETAILED SUMMARY FOR TUESDAY AUGUST 11 - SATURDAY AUGUST 15: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SUNDAY AUGUST 16 - SATURDAY AUGUST 22: Dynamical model guidance is in good agreement regarding subtropical ridging rebuilding across the south-central and southeastern U.S. late in week-1 and persisting into week-2. The 0z ECMWF, GEFS, and Canadian ensembles depict a 595-596 dm 500-hPa height maximum across the central Gulf Coast states early in the period, with weakening of the ridge likely later in week-2. This evolution favors anomalously warm temperatures across the region, with both the ECMWF and GEFS Probabilistic Extremes Tools (PETs) depicting at least a 20 percent chance maximum temperatures exceed the 90th climatological percentile. The key difference is that the GEFS focuses higher probabilities across the Southern Plains and Lower Mississippi Valley, while the ECMWF indicates these elevated chances across the Southeast. Given the large contribution from increased humidity and broadly enhanced signals in skill weighted heat risk guidance, which indicates probabilities of at least 40 (20) percent for heat index values to exceed 105 (110) deg F, a moderate risk of extreme heat is continued for Aug 16-18 from the Southern Plains eastward through the Lower Mississippi Valley and Southeast. In addition, the National Blend of Models (NBM) also depicts a number of locations with nighttime lows nearing and/or breaking daily records, where little overnight relief to daytime heat is expected. A slight risk surrounds the moderate risk area and continues for all of week-2. The progression of frontal activity adds some uncertainty across the southern Mid-Atlantic states. While the ECMWF would favor a warmer outcome and extreme heat concerns into the Carolinas, the GEFS is more progressive with relatively cooler air arriving from the north, keeping the greatest heat risk farther south. Troughing near the West Coast of the CONUS favors an influx of moisture across much of the western U.S., and expanding through the Midwest and Eastern Seaboard as evidenced by anomalous precipitable water values in the 0z ECMWF and GEFS ensembles. This is also tied to broad troughing over eastern Canada leading to enhanced westerly to northwesterly mid-level flow across the Midwest into the East, and a general progression of frontal waves or Mesoscale Convective Systems (MCSs) overtop the ridge axis situated across the south-central and southeastern states. Therefore, a slight risk of heavy precipitation is posted extending from the Four Corners, through portions of the Plains, and into the Midwest, Lower Northeast, and Mid-Atlantic. The GEFS and ECMWF PETs continue to depict at least a 20 percent chance 3-day precipitation totals exceed the 85th climatological percentile and a half-inch across the Four Corners. This region is still prone to flash flooding even with relatively small precipitation accumulations especially along dry creek beds (arroyos) and in canyons. Caution should always be exercised in such areas should thunderstorm activity initiate nearby. Pattern recognition and enhanced signals in the uncalibrated 0z ECMWF ensembles (at least a 20 percent chance 3-day precipitation exceeds 1-inch over some areas) supports the extension of the slight risk into portions of the central and eastern U.S. Later in week-2, ridging may expand into the west-central CONUS, with today's 0z ECMWF ensemble shifting the ridge center position farther west compared to yesterday, aligning more with the 0z GEFS, which depicts a 593 dm 500-hPa height maximum across the southern High Plains on day-13. This evolution would decrease the moisture advection into the West, and also promote an increase in above-normal temperatures and possibly extreme heat across portions of the Interior West and High Plains, while persisting near- to below-normal temperatures downstream across the Great Lakes and Northeast. However, uncertainty remains high given the fluctuating model guidance, as well as little to weak signals for extreme heat across the West in the PETs. A Rapid Onset Drought (ROD) risk remains designated and includes parts of Oklahoma, northeastern Texas eastward through northern Mississippi. This ROD area continues to register 30-day precipitation deficits greater than 2 inches, with little rainfall forecast during the next two weeks. Much of this ROD area is also included within the moderate risk of extreme heat as the potential for increased evapotranspiration rates also looks to reinforce this risk later in August. Across the eastern Pacific, the National Hurricane Center (NHC) is monitoring three areas located near 140 deg W, 120 deg W, and 115 deg W, with 70 percent, 40 percent, and 20 percent chances of tropical cyclone (TC) development, respectively, during the next seven days (as of 11am PDT). For the western watch area near 140 deg W, both dynamical model and Google AI guidance have been consistently favoring a mean low tracking near the Hawaiian Islands. While there continues to be much uncertainty associated with this potential TC at this lead, tools continue to indicate elevated chances for above-normal precipitation, with the ECMWF PET maintaining 20-30 percent chances for 3-day precipitation totals exceeding the 85th climatological percentile. For more info on this potential system, please refer to: https://www.nhc.noaa.gov/. FORECASTER: Thomas Collow $$