083
FXUS21 KWNC 181818
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 18 2025

SYNOPSIS: Lingering mid-level high pressure forecast over the northwestern
contiguous U.S. (CONUS) early next week is expected to bring above-normal
temperatures with extreme heat conditions possible for parts of the Pacific
Northwest and Northern Intermountain region. An accompanying risk of high winds
is also favored with coverage extending southwestward into Northern California.
Increased moisture into the southwestern CONUS brings a threat of heavy
rainfall over the Desert SW early in week-2. Wetter conditions and an increased
risk of heavy rainfall is also favored over portions of the Plains and
Mississippi Valley, limiting the risk of Rapid Onset Drought to portions of
Tennessee, Mississippi, and Arkansas. In the wake of Hurricane Erin, another
tropical disturbance tracking westward may bring high winds to parts of the
Southeast.

HAZARDS

Slight risk of extreme heat for many parts of the Pacific Northwest and
Northern Intermountain, Tue-Wed, Aug 26-27.

Slight risk of episodic high winds for parts of California, Pacific Northwest,
and the Northern Intermountain, Tue-Wed, Aug 26-27.

Slight risk of high winds for the Southeast, Tue-Fri, Aug 26-29.

Slight risk of heavy precipitation for the Desert Southwest, Tue-Thu, Aug 26-28.

Slight risk of heavy precipitation for parts of the Central and Southern
Plains, and Lower and Middle Mississippi Valley, Tue-Thu, Aug 26-28.

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

DETAILED SUMMARY

FOR THURSDAY AUGUST 21 - MONDAY AUGUST 25:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY AUGUST 26 - MONDAY SEPTEMBER 01: Based on 2-day 500-hPa height
trends, dynamical models are favoring stronger anomalous mid-level troughing
overspreading the eastern CONUS by early next week. The prevailing mean
northwesterly flow, along with a broad area of surface high pressure behind a
large frontal boundary late in week-1 is likely to bring a rush of cooler,
fall-like temperatures for many areas east of the Rockies. While this looks to
quell any extreme heat potential, above-normal 500-hPa heights upstream across
the Interior West are favored to keep daytime temperatures on the warm side, at
least through early week-2. Based on both raw and calibrated temperature tools,
the GEFS is most aggressive with the warmth throughout much of the western
CONUS, with its Probabilistic Extremes Tool (PET) depicting a broad area of at
least 20% chances for daytime temperatures exceeding the 85th percentile.
However, both the ECMWF and Canadian PETs are considerably cooler, and instead
favor any heat potential confined to the northwestern CONUS closer to the
anomalous ridge center. Both the uncalibrated and calibrated ECMWF tools show
increased chances for temperatures approaching heat risk advisory levels, and a
slight risk of extreme heat is posted for parts of the Northern Intermountain
and Pacific Northwest through Aug 27 before much of the ridging deamplifies.
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 26-27 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 also increases the wildfire risk in the
region. Later in week-2, PETs show increasing warm signals across the southern
tier of the U.S. associated with a strengthening subtropical ridge. It is
unclear whether temperatures will exceed hazard thresholds at this lead, and
this potential will be reassessed in the upcoming hazard outlooks.



As evidenced by the formation of tropical cyclone Erin and its rapid
intensification to Major Hurricane strength during the past week, the tropical
Atlantic is heating up. The National Hurricane Center (NHC) is eyeing another
potential area with 60% chances for development during the next seven days in
the wake of Erin over the western Atlantic and eastern Caribbean. Compared to
previous guidance with Erin, both GEFS and ECMWF show an increased number of
ensemble members with a more westward solution of this disturbance closer to
the southeastern U.S. There still remains a significant amount of uncertainty
in regards to any landfall potential given the aforementioned mean surface high
center that is favored to overspread this part of the country. While the GEFS
PET depicts some signal of heavy precipitation risk over the coastal Carolinas
tied to this disturbance, the ECWMF is less supportive of this risk and keeps
much of the highest rainfall totals well offshore, precluding any precipitation
hazards at this time. However, a slight risk of high winds is issued (Aug
26-29) where there is better agreement in the PETs indicating increased chances
for wind speeds exceeding the 85th percentile over eastern Gulf and the
Southeast. Both high wind and heavy precipitation potential associated with
this tropical disturbance will continue to be closely monitored this week.



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
that is expected to be favorable for increased moisture advection across much
of the southwestern CONUS. A slight risk of heavy precipitation is posted where
the GEFS and ECMWF PETs show 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 moisture also established over the Great Plains, the uncalibrated
ECMWF shows 20-40% chances of 3-day amounts exceeding an inch across parts of
Kansas, Oklahoma, Missouri, and Arkansas. Although the GEFS is drier by
comparison, both today`s 0z and 6z ensembles have trended wetter over this
region, supporting the addition of a slight risk of heavy precipitation for Aug
26-28. Due to this increased risk of heavy precipitation during week-2, as well
as increased precipitation amounts favored in the Weather Prediction Center
(WPC) week-1 QPF, coverage for the Rapid Onset Drought (ROD) risk is reduced
considerably, but remains valid for parts of the Lower Mississippi and
Tennessee Valleys in the updated outlook.



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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