351
FXUS21 KWNC 191828
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 19 2025

SYNOPSIS: Mid-level high pressure forecast over the northwestern contiguous
U.S. (CONUS) early next week is expected to bring above-normal temperatures
with an increased risk of extreme heat conditions possible for parts of the
Pacific Northwest, Northern Intermountain, and Northern High Plains. An
accompanying risk of high winds is also favored with coverage extending
southwestward into northern California. Increased moisture into the
southwestern CONUS and Great Plains brings a threat of heavy rainfall over the
Desert Southwest and over portions of the Plains and Mississippi Valley.
Possible surface low formation off the coast of the Carolinas supports an
increased risk of heavy precipitation and high winds for portions of the
Southeast and the Mid-Atlantic.

HAZARDS

Moderate risk of extreme heat for parts of the Northern Intermountain, Wed-Thu,
Aug 27-28

Slight risk of extreme heat for many parts of the Pacific Northwest, Northern
Intermountain, and Northern High Plains, Wed-Sat, Aug 27-30.

Slight risk of episodic high winds for parts of northern California, Pacific
Northwest, and the Northern Intermountain, Wed-Fri, Aug 27-29.

Slight risk of heavy precipitation for portions of the Southeast and
Mid-Atlantic, Thu-Sun, Aug 28-31

Slight risk of high winds for the Southeast and Mid-Atlantic, Thu-Sun, Aug
28-31.

Slight risk of heavy precipitation for the Desert Southwest, Wed-Fri, Aug 27-29.

Slight risk of heavy precipitation for parts of the Central and Southern
Plains, and Lower and Middle Mississippi Valley, Wed-Thu, Aug 27-28.

Rapid Onset Drought risk for parts of the Lower Mississippi and Tennessee
Valleys.

DETAILED SUMMARY

FOR FRIDAY AUGUST 22 - TUESDAY AUGUST 26:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY AUGUST 27 - TUESDAY SEPTEMBER 02: Dynamical models continue to
feature a mean ridge/trough pattern over North America, though an eastward
shift of the mean 500-hPa ridge anomaly center into western Canada, as well as
increased mean troughing expanding southwestward into Plains and Mississippi
Valley in the updated guidance is beginning to fall more in line with a
positive Pacific North America (+PNA) autumn pattern. Consequently, there is a
larger coverage of cooler temperatures favored for much of the country, with
the exception of the northwestern CONUS where temperature tools have trended
much warmer since yesterday tied to the shifted mid-level ridge center. Both
the GEFS and ECMWF Probabilistic Extreme Tools (PET) indicate elevated chances
(>40%) for daytime temperatures exceeding the 85th percentile and 95 degrees F
to support the addition of a moderate risk of extreme heat for Aug 27-28
focused over the Northern Intermountain region. A broader slight risk area of
extreme heat is posted, following the predicted positive 500-hPa height
departure fields, and valid through Aug 30 before the ridging deamplifies.
Within the highlighted area, the National Blend of Models (NBM) indicates
several locations with daytime highs or nighttime lows approaching daily
records early in week-2. With surface low pressure favored within the
highlighted region, and strong surface high pressure situated in the eastern
Pacific, periods of gusty winds are possible and a slight risk of high winds is
also posted for Aug 27-29 with coverage extending into northern California
based on tight pressure gradients favored in the ensembles. In conjunction with
dryness and above-normal temperatures favored, the wind risk is also expected
to increase the wildfire risk in the region. Later in week-2, the GEFS PET
shows increasing warm signals across the southern tier of the U.S. associated
with a strengthening subtropical ridge. However, the ECMWF maintains more
mid-level troughing and colder temperatures east of the Rockies throughout
week-2, resulting in no additional temperature related hazards being posted.



In the wake of Hurricane Erin, the National Hurricane Center (NHC) is eyeing
another potential area with 60% chances for development during the next seven
days over the western Atlantic and eastern Caribbean. Compared to yesterday,
there is less support in the deterministic and ensemble member solutions
favoring a westward track nearing the southeastern CONUS. This is likely due to
weaker mean subtropical ridging favored, allowing for this disturbance to
recurve over the Atlantic. However, these solutions are also beginning to point
to a secondary surface low potentially forming off the coastal Carolinas by
days 9 and 10, which looks to keep some risk of heavy precipitation and high
winds over the Southeast and Mid-Atlantic, albeit slightly later in the week-2
period. Based on the GEFS and ECMWF PETs, a slight risk of heavy precipitation
is posted over the lower Eastern Seaboard for Aug 28-31 where there are at
least 20% chances for 3-day rainfall amounts exceeding the 85th percentile and
1 inch. An accompanying slight risk of high winds also remains posted, valid
for the same period, with its coverage removed over the coastal Gulf of
America.



Model guidance and tools continue to favor an approaching mid-level trough over
the eastern Pacific, as well as a renewed potential for tropical cyclone
activity in the eastern Pacific early in week-2. These features are expected to
be favorable for increased moisture advection across much of the southwestern
CONUS, which is well reflected in the GEFS and ECMWF PETs. A slight risk of
heavy precipitation remains posted (Aug 27-29) where there are increased
chances for 3-day precipitation amounts exceeding the 85th percentile with
pockets of total amounts exceeding a half an inch consistent with monsoonal
thunderstorm activity. Any locally heavy monsoonal rainfall may lead to flash
flooding in the highlighted area.



With increased tropospheric moisture also favored further east over the Great
Plains, surface low pressure development and/or stalled frontal forcing on the
backside of a mean surface high situated over the Midwest is expected to bring
enhanced precipitation amounts late in week-1 and heading into week-2.
Consistent with previous guidance, the ECMWF is stronger with the heavy
precipitation threat, but both raw and calibrated tools remain supportive of a
continued slight risk of heavy precipitation over portions of the Plains and
Mississippi Valley, remaining valid through Aug 28. Relative to yesterday, this
slight risk is shifted further southward to include portions of Oklahoma and
Texas where there are higher chances for 3-day rainfall amounts exceeding an
inch. Further east, a Rapid Onset Drought (ROD) risk remains designated over
the parts of Tennessee, Mississippi, Arkansas where soil moisture content is
registering in the lowest percentiles and comparatively drier conditions are
favored during the next two weeks.



No hazards are issued over Alaska. A strong trough/ridge pattern oriented north
to south is expected to bring above-normal, but non hazardous precipitation
amounts for much of the Mainland, with drier conditions favored across the
Southeast.

FORECASTER: Nick Novella

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