616
FXUS21 KWNC 201818
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 20 2025

SYNOPSIS: Forecast mid-level high pressure over the northwestern contiguous
U.S. (CONUS) 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, Thu, Aug
28.

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

Slight risk of extreme heat for many parts of the Pacific Northwest, Northern
Intermountain, and Northern High Plains, Thu-Sat, Aug 28-30.

Slight risk of episodic high winds for parts of northern California, Pacific
Northwest, and the Northern Intermountain, Thu-Sat, Aug 28-30.

Slight risk of heavy precipitation for parts of the Central and Southern
Plains, and Lower and Middle Mississippi Valley, Thu-Fri, Aug 28-29.

Slight risk of heavy precipitation for the Desert Southwest, Thu-Fri, Aug 28-29.

Slight risk of heavy precipitation for portions of the Southeast and
Mid-Atlantic, Thu-Mon, Aug 28-Sep 1

Slight risk of high winds for the Southeast and Mid-Atlantic, Thu-Mon, Aug
28-Sep 1

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

DETAILED SUMMARY

FOR SATURDAY AUGUST 23 - WEDNESDAY AUGUST 27:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY AUGUST 28 - WEDNESDAY SEPTEMBER 03: Towards the middle of next
week, the 0z ECMWF and 0z GEFS ensemble mean 500-hPa height forecasts appear in
fair agreement, with both featuring an amplified ridge center over western
Canada, shallow troughing off the West Coast of the U.S., and anomalous
troughing overspreading the northeastern quarter of the CONUS. By Labor Day
weekend, these mean solutions begin to diverge, where the GEFS generally favors
a more progressive and deamplified pattern over the CONUS. By contrast, the
ECMWF maintains a more amplified ridge center over western Canada, with deeper
mean troughing downstream persisting over eastern North America that results in
colder temperature solutions compared to the GEFS over the course of the
period. Therefore, forecast confidence is greatest early in week-2, as the
updated outlook focuses on a number of potential temperature and precipitation
hazards that are favored to linger from week-1 into the week-2 period.



Tied to the amplified ridging over the northwestern CONUS, a moderate risk of
extreme heat remains issued, and valid through Aug 28, where the Probabilistic
Extreme Tools (PETs) continue to depict elevated chances (30-40%) for maximum
daytime temperatures exceeding the 90th climatological percentile and 95
degrees F. A broader slight risk area of extreme heat is posted through Aug 30,
and is expanded eastward into the Northern Plains in deference to the more
progressive ridging favored in the GEFS. With the hot temperatures driving
deeper thermal low pressure over eastern Washington, and mean surface high
pressure situated in the eastern Pacific, periods of gusty winds are possible
and a slight risk of high winds remains posted for Aug 28-30. Given antecedent
dryness and above-normal temperatures favored in the region, any episodes of
high winds are also expected to increase wildfire activity. Multiple wildfires
are currently ongoing within the highlighted wind risk area that have yet to be
fully contained.



An approaching mid-level trough over the eastern Pacific, as well as an
increased potential for tropical cyclone activity to the southwest of Mexico
early in the period, looks to provide a favorable setup for increased moisture
advection across much of the southwestern CONUS. Based on raw and calibrated
precipitation tools, much of the heavy precipitation threat has begun to time
off in week-1, however the ECMWF PET maintains at least 20% chances for amounts
exceeding the 85th percentile and a half inch over the Desert Southwest early
in week-2. With elevated surface dewpoints also favored in the ECMWF over
southern Arizona conducive for monsoonal thunderstorms late next week, this
supports the continuation of the slight risk of heavy precipitation for Aug
28-29. Any locally heavy monsoonal rainfall may lead to flash flooding in the
highlighted area.



Increased tropospheric moisture is also favored east of the Rockies, where
stalled frontal forcing on the backside of a mean surface high situated over
the Midwest is expected to bring enhanced precipitation amounts over parts of
the Plains and Mississippi Valley late in week-1 and heading into week-2.
Consistent with previous PET guidance, the ECMWF remains more robust with the
heavy precipitation threat than the GEFS, indicating 30-40% chances for 3-day
amounts exceeding the 85th. In consideration of WPC QPF favoring over 2 inches
of precipitation in Kansas and Oklahoma on days 6 and 7, and increased signals
in the uncalibrated ECMWF for additional amounts exceeding an inch, likely due
to stronger surface high pressure shifting eastward to induce more return flow
from the Gulf into the Plains early in the period, a moderate risk of heavy
precipitation is introduced in the updated outlook for Aug 28. A broader slight
risk area of heavy precipitation remains designated and is extended through Aug
29. Further east, Rapid Onset Drought (ROD) risk remains valid for week-2 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.



Behind Hurricane Erin in the tropical Atlantic, the National Hurricane Center
(NHC) continues to monitor another disturbance with 60% chances for development
during the next seven days over the western Atlantic and eastern Caribbean. The
latest NHC Tropical Weather Outlook continues to advertise a recurving track
associated with this potential system, however model solutions also point to a
secondary surface low potentially forming off the coastal Carolinas early in
week-2, which looks to keep some risk of heavy precipitation and high winds
over the Southeast and Mid-Atlantic. Based on the GEFS and ECMWF PETs, a slight
risk of heavy precipitation is posted over the lower Eastern Seaboard for Aug
28-Sep 1 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.



No hazards are issued over Alaska. Anomalous mean troughing predicted over the
Bering Strait and resultant onshore flow is likely to keep much of the Mainland
above normal in regards to precipitation. This is reflected in the PETs with
increased chances for amounts exceeding the 85th percentile, though odds remain
low that any totals reach hazard thresholds.

FORECASTER: Nick Novella

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