700
FXUS21 KWNC 161807
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 16 2026

SYNOPSIS: A major, long duration period of extreme heat is expected to persist
into week-2 across the central CONUS and a large part of the Nation`s southern
tier. Models converge most strongly on the Red River (South) Valley, most of
Oklahoma, and some adjacent areas early in the period, where a high risk for
extreme heat is posted. At least a slight risk of extreme heat covers most of
the southern tier of the Nation from the Desert Southwest to the South Atlantic
Coast. Anomalous mid-level high pressure near the Four Corners is forecast in
concert with an incursion of Gulf moisture, producing high heat index values.
This mid-level high pressure is favored to drift slowly westward or
southwestward while deamplifying, ending the extreme heat risk late week-2.
Meanwhile, given antecedent dryness, the above-normal temperatures and
subnormal rainfall expected for next two weeks support a Rapid Onset Drought
(ROD) risk for portions of the Central and Southern Plains and Middle and Lower
Mississippi Valley.

HAZARDS

High risk of extreme heat for the Red River (South) Valley, much of Oklahoma,
and some adjacent areas, Mon-Tue, Aug 24-25.

Moderate risk of extreme heat for much of the Central and Southern Plains,
parts of the Lower Mississippi and Tennessee Valleys, and adjacent Southeast,
Mon-Wed, Aug 24-26.

Slight risk of extreme heat for portions of the Southwest, Southern Rockies,
Central and Southern Plains, Lower Mississippi and Tennessee Valleys, and
Southeastern CONUS, Mon-Fri, Aug 24-28.

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

DETAILED SUMMARY

FOR WEDNESDAY AUGUST 19 - SUNDAY AUGUST 23:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR MONDAY AUGUST 24 - SUNDAY AUGUST 30: Dynamical models remain in good
agreement regarding subtropical ridging across the south-central to
southwestern U.S. through most of week-2. The 0z European ensemble (ECENS),
GEFS, and Canadian ensemble (CMCE) means all start the period with a 596 dm
500-hPa height maximum centered near the south-central CONUS or eastern Four
Corners region. The ECENS and GEFS are in excellent agreement placing the
center of this feature over northern or eastern New Mexico while the CMCE mean
depicts this feature over the Red River (South) Valley, but the slightly
farther west placement is favored since it is the majority solution, and more
consistent with earlier runs. Meanwhile, ensemble means depict a somewhat
stronger and more persistent mid-level trough over the northeastern CONUS
relative to yesterday. The CMCE mean is strongest with this feature and the
ECENS mean the weakest, with the GEFS mean splitting the difference. The GEFS
mean, which approximately equals the average of all three ensemble means, is
favored with this mid-level trough.



Over the course of week-2, the 500-hPa height center remains roughly in place
over the central and southwestern CONUS while slowly flattening and
deamplifying. Today`s model consensus shows this process happening more slowly
than depicted yesterday, and also starts the period with a slightly more
amplified mid-level ridge. As a result, the forecast of a long-duration heat
event is maintained. The longer-lived and more-amplified mid-level ridge
depicted today, along with good agreement among the Probabilistic Extremes
Tools (PETs), prompted posting a high risk of extreme heat where model guidance
converges most strongly, namely the Red River (South) Valley, much of Oklahoma,
and some adjacent areas early week-2 (Mon-Tue Aug 24-25). The moderate risk of
extreme heat is longer-lasting and slightly more expansive than yesterday,
covering the southern halves of the Plains and Mississippi Valley, the
Tennessee Valley, and the adjacent Southeast. After shifting westward
yesterday, the ensemble means support a shift back toward the east today. This
is especially true in the European ensemble (ECENS) mean, which lets the center
of the 500-hPa ridge drift eastward into the southern Plains before it weakens
and sinks toward the Mexico/New Mexico Border. The Canadian ensemble (CMCE) and
the GEFS maintain the center of the mid-level ridge farther west, consistent
with yesterday`s GEFS and ECENS mean. Since the GEFS mean has been most
consistent over the past few runs, and because it is the majority solution, the
official forecast favors less of a jog to the east than forecast by the ECENS
mean, but it has moved slightly in that direction. This scenario supports
expanding the slight risk area farther up the East Coast than yesterday,
through most of Georgia and South Carolina. The slight risk is removed after
Fri Aug 28, in concert with the deteriorating mid-level ridge.



Both the GEFS and ECENS PETs depict at a 40 to 70 percent chance of maximum
temperatures exceeding the 85th climatological percentile early week-2 over the
Red River (South) Valley, Oklahoma, and some adjacent areas. This coincides
with the posted high risk of extreme heat, and is slightly more robust in the
ECENS PET than yesterday. The PETs show progressively decreasing odds for
extreme heat with time, but the ECENS PET keeps higher chances for extreme heat
farther east after the first day of the period. Again, the GEFS PET is favored,
but some credence has been given to the ECENS since it resembles the consensus
from a couple days ago.



Increased humidity is expected to contribute to extreme heat index values from
the Southern Plains eastward, with a strong signal in the calibrated
skill-weighted GEFS-ECMWF heat risk guidance, particularly across the Lower
Mississippi Valley and parts of the Southeast, where the heat index may exceed
the actual temperature by 10 deg F or more, according to internal heat index
guidance from both the GEFS and ECENS. Probabilities for heat index values to
top out at 105 deg F or higher exceed 70 percent in parts of this region, and
the chances for maximum heat index values over 110 deg F exceed 50 percent in
South Texas and the Lower Colorado Valley, and ranges from 20 to 40 percent
across Oklahoma, southernmost Kansas, Louisiana, Mississippi, Arkansas,
northern Texas, and some areas near the Gulf Coast. In addition, the National
Blend of Models (NBM) depicts nighttime lows nearing or breaking daily records
early week-2 from southern Florida to southern California, resulting in little
overnight relief from daytime heat.



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 over the Four Corners, especially the higher elevations of Colorado.
Confidence in a healthy monsoon remains high, but conditions do not appear
robust enough to reach hazards thresholds, so no hazards are posted. Still,
isolated areas of heavy rain remain possible, and this region is prone to flash
flooding even with relatively low rainfall  totals along dry creek beds
(arroyos) and in canyons. Caution should always be exercised in such areas if
thunderstorm activity is initiated nearby. Also, some convective activity may
result in little or no rainfall while still being capable of generating
lightning, which poses a risk of wildfire initiation.



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
(near or under half of normal), with little rainfall expected during the next
two weeks. Furthermore, much of this ROD area is within the moderate risk of
extreme heat. This could potentially increase evapotranspiration rates and
accelerate surface moisture depletion.

FORECASTER: Rich Tinker

$$