210
FXUS21 KWNC 141821
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 14 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 near
the Four Corners combined with Gulf moisture to produce high heat indices.
Mid-level high pressure is favored to spread westward, increasing the risk for
extreme heat in the Desert Southwest. 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.

HAZARDS

Moderate risk of extreme heat for portions of the Southern Plains, Lower
Mississippi and Tennessee Valleys, and Southeastern U.S., Sat-Sun, Aug 22-23.

Slight risk of extreme heat for portions of the Central and Southern Plains,
Middle and Lower Mississippi and Tennessee Valleys, and Southeastern U.S.,
Sat-Thu, Aug 22-27.

Slight risk of extreme heat for portions of the Desert Southwest, Sat-Wed, Aug
22-26.

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

DETAILED SUMMARY

FOR MONDAY AUGUST 17 - FRIDAY AUGUST 21:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY AUGUST 22 - FRIDAY AUGUST 28: Dynamical model guidance remains in
good agreement regarding subtropical ridging persisting across the southwestern
U.S. through week-2. The 0z ECMWF, GEFS, and Canadian ensembles depict a
594-596 dm 500-hPa height maximum retrograding into the Intermountain West
early in 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 40 percent chance of maximum temperatures exceeding the 85th
climatological percentile through the middle of week-2 centered across the
Central Gulf Coast states. The ECMWF and GEFS continue to depict a ridge
retrogression, now mostly in week-1, with the ridge axis established over the
Four Corners by the start of week-2. 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 in
some locations. 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. A moderate risk for
extreme heat remains valid through Aug 23 and continues to extend into the
Southern Plains where there is increased potential for heat index values to
exceed 105 deg F. A slight risk surrounds the moderate risk area and covers Aug
22-27.



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. However over the last several days a
reduction in signal strength has been noted. With model solutions generally
indicating a weakening of troughing along the West Coast, a gradual reduction
in monsoon activity seems increasingly likely. Therefore the slight risk of
heavy precipitation from yesterdays outlook has been discontinued. However,
isolated areas of heavy rain remain possible and 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. Finally,
as monsoon moisture declines, any continued convective activity may result in
relatively little rainfall while still being capable of generating lightning,
which can pose a risk of wildfire initiation.



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.
Daily maximum temperatures from multiple model ensembles exceed 105F across the
Sonoran and Mojave deserts through the middle of week-2, after which indicated
maximum temperatures moderate somewhat. Increased humidity from the monsoon is
likely to result in relatively muggy conditions for the area. Therefore a
slight risk of extreme heat is posted for much of the Desert Southwest and
extending into central New Mexico, valid Aug 22-26.



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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