776
FXUS21 KWNC 111809
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 11 2026

SYNOPSIS: A major, long duration period of extreme heat continues to be
predicted across portions of the south-central contiguous U.S. (CONUS) and
Southeast persisting into week-2 tied to anomalous mid-level high pressure
combined with high humidity levels. Model guidance has continued to support a
very strong heat event across the south-central and southeastern CONUS.
Antecedent dryness, combined with little precipitation favored over the next
two weeks supports a Rapid Onset Drought (ROD) risk for portions of the Central
and Southern Plains and Middle and Lower Mississippi Valley. Enhanced monsoonal
activity continues to be indicated across the Four Corners, although with less
certainty with downstream progression across the Midwest as some of the
stronger signals have now shifted into week-1.

HAZARDS

High risk of extreme heat for portions of the Central and Southern Plains,
Middle and Lower Mississippi Valley, and Southeast, Wed-Fri, Aug 19-21.

Moderate risk of extreme heat for portions of the Central and Southern Plains,
Middle and Lower Mississippi and Tennessee Valleys, Southeast, and southern
Mid-Atlantic, Wed-Sat, Aug 19-22.

Slight risk of extreme heat for portions of the Central and Southern Plains,
Middle and Lower Mississippi and Tennessee Valleys, Southeast, and southern
Mid-Atlantic, Wed-Tue, Aug 19-25.

Slight risk of heavy precipitation for portions of the Four Corners, Wed-Sun,
Aug 19-23.

Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains
and the Middle and Lower Mississippi Valley.

DETAILED SUMMARY

FOR FRIDAY AUGUST 14 - TUESDAY AUGUST 18:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY AUGUST 19 - TUESDAY AUGUST 25: Dynamical model guidance remains
in good agreement regarding subtropical ridging persisting across the
south-central and southeastern U.S. into week-2. The 0z ECMWF, GEFS, and
Canadian ensembles depict a 594-596 dm 500-hPa height maximum slowly
retrograding from the Southeast to the Southern Plains throughout the period,
with its amplitude steady or even increasing slightly. As a result, confidence
remains high for a long duration heat event, with many tools indicating the
potential for oppressive conditions lingering well into late August. Both the
GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict at least a 60 percent
chance of maximum temperatures exceeding the 85th climatological percentile at
the start of week-2 centered across the Central Gulf Coast states, and
remaining above 40 percent through the middle of week-2. The ECMWF and GEFS
both continue to indicate a retrogression of the ridge axis during week-2,
although the GEFS is more bullish in this scenario than the ECMWF, which was
more aggressive yesterday. These discrepancies are minor though and in sum the
forecast confidence remains high with a consistent trend in model guidance. A
large contribution from increased humidity is expected, with a strong signal in
the calibrated skill-weighted GEFS-ECMWF heat risk guidance, particularly
across the Central and Southern Plains and adjacent Mississippi Valley where
probabilities exceed 60 percent for maximum heat index values to exceed the
95th climatological percentile. A high risk of extreme heat is forecast for the
Central Plains, Middle Mississippi Valley, and the Southeast, where heat index
values may exceed 110 deg F, and is valid Aug 19-21. In addition, the National
Blend of Models (NBM) also depicts a number of locations with nighttime lows
nearing and/or breaking daily records, resulting in little overnight relief
from the daytime heat. The moderate risk for extreme heat remains valid through
Aug 22 and continues to extend into the Central Plains where there is increased
potential for heat index values to exceed 105 deg F. A slight risk surrounds
the moderate risk area and continues for all of week-2.



Troughing initially near the West Coast of the CONUS favors an influx of
moisture across much of the western U.S., and enhanced Southwest Monsoon
activity continuing over the Four Corners where the GEFS and ECMWF PETs depict
at least a 20 percent chance 3-day precipitation exceeds the 85th
climatological percentile and a half-inch early in week-2. The ECMWF maintains
this signal through the forecast period, while the GEFS drops below these
thresholds by midweek. With model solutions generally indicating a weakening of
troughing along the West Coast a gradual reduction in monsoon activity seems
more likely. Therefore, a slight risk of heavy precipitation is posted for
portions of the Desert Southwest, Great Basin, and the Southern and Central
Rockies, valid Aug 19-23. This region is 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.



Toward the middle of week-2, troughing along the West Coast is favored to
retreat with rising heights across the West tied to expansion of the ridging
over the south-central CONUS. 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
where the GEFS PET depicts increasing coverage of probabilities greater than 20
percent for maximum temperatures to exceed the 85th climatological percentile.
However, due to lower probabilities in the ECMWF PET, no related extreme heat
hazards are posted across the West at this time.



A Rapid Onset Drought (ROD) risk remains designated across portions of the
Central and Southern Plains and Middle and Lower Mississippi Valley. 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.

FORECASTER: Danny Barandiaran

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