730
FXUS21 KWNC 051823
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 05 2025

SYNOPSIS: The favored development of mid-level high pressure across central
North America next week is anticipated to result in a pattern change, with
above-normal temperatures returning across portions of the central contiguous
U.S. (CONUS), and possible extreme heat conditions emerging across parts of the
Mississippi, Tennessee, and Ohio Valleys during week-2.  Lingering mid-level
low pressure is forecast over the western third of the CONUS early in the
period favoring enhanced wind speeds over parts of the Southwest and extending
through the Great Plains. A stalled frontal boundary remains forecast across
the southeastern U.S. bringing an increased likelihood for enhanced
precipitation and high winds. Surface low pressure is forecast to bring
increased chances of elevated wind speeds to southern and southeastern coastal
Alaska.

HAZARDS

Slight risk of extreme heat across portions of the Central Plains, Middle
Mississippi Valley, and Ohio Valley, Sat-Tue, Sep 13-16.

Slight risk of high winds over parts of the southwestern U.S. into the Central
and Southern Rockies and Great Plains, Sat, Sep 13.

Slight risk of heavy precipitation across the Florida Peninsula and coastal
Southeast, Fri-Sun, Sep 13-15.

Slight risk of high winds across Florida, the eastern Gulf Coast, and portions
of the Mid-Atlantic and Southeast coasts, Sat-Mon, Sep 13-15.

Slight risk of high winds across coastal portions of southern and southeastern
Alaska, Sat-Wed, Sep 13-17.

Rapid Onset Drought risk across portions of the Lower Mississippi and Tennessee
Valleys.

DETAILED SUMMARY

FOR MONDAY SEPTEMBER 08 - FRIDAY SEPTEMBER 12:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY SEPTEMBER 13 - FRIDAY SEPTEMBER 19: Mean 500-hPa height anomaly
forecasts from the 0z GEFS and ECMWF ensembles show the week-2 period starting
off with an amplified ridge center over southcentral Canada, bookended by a
pair of weak troughs over the western and northeastern CONUS.  These two latter
mid-level features remain favored to weaken over time, where there is fair
model agreement featuring anomalous ridging building back into the western
CONUS later in the period.  Such a pattern evolution would look to keep
temperatures on the warm side, with mostly tranquil weather for much of the
CONUS heading towards the autumn equinox. Further north though, stronger mean
troughing favored in the dynamical models over the Gulf of Alaska would favor
more unsettled weather over western Canada and into Alaska during week-2.



In response to the mid-level ridge axis extending from central Canada into the
Midwest late next week, both raw and calibrated temperature tools continue to
highlight elevated chances for above-normal temperatures focused over the
Middle Mississippi, Tennessee, and Ohio Valleys. Probabilistic Extreme Tools
(PETs) from the GEFS and ECWMF depict at least 20% chances for daytime
temperatures exceeding the 90th percentile and 90 degrees F, supporting the
continuation of a slight risk of extreme heat, remaining valid through Sep 16.
Based on increased temperature signals in the PETS over the Ohio and Tennessee
Valley, the slight risk area is expanded northeastward closer towards the
Appalachians in the updated outlook.  For many areas within the highlighted
region, this would mark a swift return of summer-like temperatures following a
fall-like cooldown favored during week-1. PETs also show heat signals further
south into the Southern Plains and Mississippi Valley, however, temperatures
are not expected to reach the higher heat thresholds for this part of the
country for mid-September. The combination of above-normal temperatures and
below-normal precipitation forecast also supports a Rapid Onset Drought (ROD)
risk posted mainly over parts of Mississippi and Alabama where many local areas
are registering less than half their normal rainfall accumulation over the past
60 days.



At the base and ahead of the aforementioned troughing predicted over western
CONUS early in week-2, a slight risk of high winds remains posted over portions
of the California Coast, Great Basin, Southwest, and the Central and Southern
Rockies and Plains for Sep 13. Although this troughing is favored to deamplify
by the outset of week-2, any additional episodes of high winds could prolong
the risk for wildfire development due to very low soil moisture values being
registered for many parts of the West.  The mid-level feature is also likely to
bring enhanced precipitation amounts for much of the northwestern CONUS, where
the ECMWF PET maintains considerably high (40-60%) signals for 3-day amounts
exceeding the 85th percentile, with 20% chances of amounts exceeding an inch
over the Pacific Northwest early in week-2. The GEFS PET is comparatively more
subdued with this potential, and given that any increased signals in percentile
space are the result of low precipitation climatologies for this time of year,
with actual amounts remaining below hazardous thresholds, no corresponding
hazards are issued. If anything, any rainfall above climatology would provide
needed relief to many areas in the northwestern CONUS that are experiencing
moderate to extreme drought conditions based on the latest U.S. drought
monitor.



Over the southeastern CONUS, stalled frontal activity predominately favored
during week-1 looks to persist into week-2, serving as a focus for continued
enhanced precipitation. Compared to previous guidance, both the uncalibrated
and calibrated ECMWF shunt the highest precipitation amounts further south and
offshore of Florida, whereas the GEFS maintains more of a northerly solution of
the heavy precipitation potential. Due to the persistence of this surface
forcing feature, with continued signs of weak troughing aloft, a slight risk of
heavy precipitation along with a slight risk of high winds remains issued, both
now valid through Sep 15.  Consistent with previous thinking, surface low
formation along the frontal boundary cannot be ruled out which could bring a
lingering risk of precipitation and high winds to parts of the Eastern Seaboard
and eastern Gulf coast.



Across the Main Development Region (MDR) of the tropical Atlantic, the National
Hurricane Center (NHC) continues to eye a tropical disturbance (Invest 91L)
with 40% (70%) for development during the next 48 hours (seven) days, as of 2pm
EDT. While there has been more of a westward trend in the ensemble member low
tracks since yesterday, this morning`s 0z deterministic and ensemble solutions
now struggle to maintain much deepening as the low approaches the lesser
Antilles next week. Still, this is a novel development, and it is far too early
to determine if any impacts will occur, and this potential system will continue
to be closely monitored in the upcoming outlooks.



Likely tied to tropical cyclone Peipah in the western Pacific becoming absorbed
in the extratropical westerlies, stronger mid-level troughing and associated
mean surface low pressure looks to bring enhanced precipitation with
potentially hazardous high winds to parts of south-central and southeastern
coastal Alaska during week-2. The ECMWF PET depicts 20% to 40% chances of wind
speeds exceeding the 85th climatological percentile and 40-mph across southern
and southeastern coastal Alaska during the early and middle parts of the
period. Therefore, a slight risk of  high wind is highlighted across this area,
Sep 13-17. No associated precipitation related hazards are posted due to the
PETs showing little to no signal for accumulated amounts reaching hazardous
thresholds in percentile space.

FORECASTER: Nick Novella

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