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

$$