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

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