199
FXUS21 KWNC 291804
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 29 2025

SYNOPSIS: Late in week-1 into the outset of week-2, dynamical models are in
good agreement regarding a robust area of mid-level low pressure developing
across the Great Lakes and Northeast. This feature is likely to bring weather
more typical of early Fall. As surface high pressure builds over the Northeast,
enhanced easterly flow is favored across the Southeast, with a wavering frontal
system contributing to periods of unsettled weather across the Gulf and
Southeast Coasts including Florida. Over the Southwest, potential tropical
cyclone development west of Mexico could enhance tropical moisture, increasing
the potential for episodes of locally heavy precipitation for the region early
in the period.

HAZARDS

Slight risk of heavy precipitation across Florida, the Gulf Coast, and coastal
portions of the Carolinas and Southeast, Sat-Fri, Sep 6-12.

Slight risk of heavy precipitation across parts of the Desert Southwest,
Sat-Mon, Sep 6-8.

Slight risk of high winds across portions of the Great Lakes, Ohio Valley, and
Northeast, Sat, Sep 6.

Slight risk of high winds across portions of eastern California and central
parts of Washington and Oregon, Sat-Sun, Sep 6-7.

Slight risk of high winds across portions of the coastal Southeast, Florida,
and the Gulf Coast,  Sat-Wed, Sep 6-10.

Slight risk of much below normal temperatures across portions of the Upper
Mississippi Valley and Great Lakes, Sat-Sun, Sep 6-7.

DETAILED SUMMARY

FOR MONDAY SEPTEMBER 01 - FRIDAY SEPTEMBER 05:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY SEPTEMBER 06 - FRIDAY SEPTEMBER 12: Late in week-1, a highly
amplified 500-hPa height pattern is predicted across North America, with strong
ridging across the Gulf of Alaska and western Canada, and troughing downstream
over the eastern U.S. These features are forecast to persist into the beginning
of week-2 before slowly weakening. The ridging over western North America
favors anomalous warmth across the Northwest, with extreme heat concerns prior
to the start of week-2. While above-normal temperatures are still likely during
week-2, the signals for extreme heat diminish compared to the late week-1
timeframe, with most areas having probabilities less than 20 percent for
temperatures above 95 deg F in the ECENS and GEFS Probabilistic Extremes Tools
(PETs). Therefore, the extreme heat risk is discontinued. However, the
above-normal temperatures still support thermal low pressure forming across the
West Coast states, with adjacent surface high pressure over the Northeast
Pacific leading to an enhanced pressure gradient. Therefore, a slight risk of
high winds is posted for parts of eastern California and central parts of
Washington and Oregon, Sep 6-7. Anticipated hot and dry conditions may lead to
enhanced wildfire risk across interior portions of the Northwest and northern
California.



Downstream over the north-central and northeastern CONUS, the big story is
predicted to be an early Fall-like weather pattern associated with an amplified
trough moving across the region. The initial front and associated precipitation
is likely to move through prior to week-2. However, behind this front, gusty
winds are anticipated over the Great Lakes, Ohio Valley, and Northeast. The
ECENS PET depicts a 20-40 percent chance wind speeds exceed the 85th
climatological percentile over these areas. While the highest wind speeds are
favored on the eastern shores of the Great Lakes and the Northeast coastal
waters, the entire area is highlighted with a slight risk for high winds on
day-8 (Sep 6). The temperature forecast is more uncertain given that the PETs
are significantly colder compared to the uncalibrated guidance. In particular,
the ECENS PET depicts probabilities exceeding 20 percent for minimum
temperatures in the lowest 15th climatological percentile and below 40 deg F
over much of the Upper Mississippi Valley, Great Lakes, and into parts of the
Interior Northeast. However, the uncalibrated 0z GEFS and ECENS indicate
minimum temperatures remaining in the 40s deg F over most areas. The
deterministic 0z ECMWF and 6z GFS are generally in line with their warmer
uncalibrated ensemble solutions, with the 0z GFS being on the colder side of
the envelope. Todays forecast maintains the slight risk of much below normal
temperatures over portions of the Upper Mississippi Valley and Great Lakes, Sep
6-7, where the coldest temperatures are predicted. While it is uncertain the
extent of areas that get below 40 deg F, any isolated areas that dip into the
30s deg F could be at risk for frost over susceptible vegetation. A quick
moderation is forecast by the second half of week-2, with above-normal
temperatures becoming more likely as the mid-level flow pattern becomes more
zonal.



The aforementioned front is forecast to become quasi-stationary across the Gulf
Coast and Southeast during week-2, with surface high pressure over the
Northeast also favoring enhanced easterly flow across the Southeast. As a
result, unsettled weather is likely over these areas throughout the period, in
the form of episodic heavy precipitation and potentially elevated wind speeds.
Uncalibrated guidance from the 0z ECENS and GEFS generally depicts the heaviest
precipitation amounts just offshore, but it would not take much of an
adjustment to bring these higher totals to the coast. The GEFS and ECENS PETs
depict at least a 20 percent chance 3-day precipitation totals exceed the 85th
percentile and 1-inch along the Gulf and Southeast coasts throughout week-2.
Initially the strongest signals are depicted across southern Texas, the Lower
Mississippi Valley, and the coastal Southeast, before becoming consolidated
across the entire Gulf Coast by the middle of the period. Therefore, a slight
risk of heavy precipitation is posted over all of these areas for the entire
period. Additionally, the ECENS PET depicts parts of the Southeast and central
Gulf coasts having at least a 20 percent chance wind speeds exceed the 85th
percentile and 25-mph supporting a slight risk of high winds, Sep 6-10.



Tropical cyclone development is likely across the East Pacific during the next
week, with the potential of at least one system to track northwestward, with
the ECENS tracking closer to Baja California and the GEFS farther offshore. A
more northerly component of the track is likely to enhance moisture over parts
of the Southwest leading to elevated chances of heavy precipitation. Despite
high uncertainty of the timing and possible impact of enhanced moisture from
possible tropical cyclones, a slight risk of locally heavy precipitation is
highlighted for parts of Arizona and southwestern New Mexico, Sep 6-8,
primarily based on guidance from the PETs.



Mid-level positive 500-hPa height departures are predicted for the mean week-2
pattern for Alaska, supporting above normal temperatures for much of the state.
Although anomalously warm temperatures are anticipated, actual temperatures are
not forecast to reach hazardous thresholds.

FORECASTER: Thomas Collow

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