059
FXUS21 KWNC 171832
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 17 2026

SYNOPSIS: Mid-level low pressure situated offshore of the West Coast, as well
as lingering frontal activity and potential surface low development in the Gulf
supports an increased risk of heavy precipitation over the parts of the Four
Corners, eastern Great Plains, and the southeastern CONUS early in week-2. A
continuation of enhanced, and possibly heavy precipitation from week-1 into
week-2 may lead to flooding across parts of the Four Corners.

HAZARDS

Slight risk of heavy precipitation for portions of the lower Mid-Atlantic,
Southeast and Lower Mississippi Valley, Fri-Thu, Sep 25-Oct 1.

Slight risk of heavy precipitation for parts of the Southwest, southern
Rockies, and Southern High Plains, Fri-Sat, Sep 25-26.

Flooding possible for portions of the Four Corners region.

DETAILED SUMMARY

FOR SUNDAY SEPTEMBER 20 - THURSDAY SEPTEMBER 24:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY SEPTEMBER 25 - THURSDAY OCTOBER 01: Relative to previous ensemble
guidance, dynamical models have come into better agreement in the regards to
the shape and evolution of the 500-hPa pattern later next week. A strong
mid-level ridge center is favored to be established over southcentral Canada
with an amplified ridge axis overspreading much of central North America,
bookended by a pair of troughs over the eastern Pacific and eastern U.S.
Concurrent with a favored weakening of the mean eastern Pacific troughing,
models show much of the eastern U.S. troughing become more amplified early in
week-2. With a deepening trough axis situated along the eastern Seaboard,
cooler and drier conditions are favored for many areas over the northeastern
CONUS, however frontal activity as well as surface low development looks to
remain a factor in regards to heavy precipitation risks mainly across the
southeastern CONUS during the period. Upstream, rising heights over the
southwestern CONUS supports the development of drier surface conditions over
the Four Corners, however multiple tools continue to show a lingering
likelihood for enhanced moisture advection possibly tied to Tropical Cyclone
(TC) activity in the eastern Pacific. Later in week-2, ensembles indicate a
continuation of the Omega-like pattern gradually deamplifying over time, though
the GEFS maintains stronger mean troughing over the eastern U.S. than the ECENS
with lowering heights over the Gulf supportive of continued unsettled weather.




Tied to the deepening trough over the eastern U.S., the GEFS and ECENS differ
in regards to the position of the mean frontal boundary early in the period.
The GEFS maintains an increased heavy precipitation risk over the coastal Gulf
and Eastern Seaboard, whereas the ECENS favors a more offshore focused solution
of the mean boundary with comparably lower precipitation amounts onshore. By
the middle of week-2, however, both the raw and calibrated ECENS depict
increasing signals for heavy precipitation  across the Gulf through late
September, possibly associated with surface low development on the trailing end
of the mean frontal boundary extending from the Gulf into the western Atlantic.
While this pattern is less supported in the GEFS PET, its uncalibrated tools
also favor an uptick in precipitation amounts in the Gulf, which is supported
by lowering mid-level heights in the model. Therefore, to reconcile these model
differences and to capture an evolving heavy precipitation threat, a slight
risk of heavy precipitation remains posted for the entirety of week-2. Based on
a convergence of evidence in the tools, the slight risk area now covers the
central Gulf Coast, with coverage removed over much of the Mid-Atlantic in the
updated outlook. Due to antecedent dryness and drought conditions being
registered within the highlighted slight risk area, any enhanced precipitation
may prove to be beneficial in alleviating dry soils, though local, urban
flooding is also possible should heavy precipitation be realized. The heavy
precipitation risk is also supported by observed Sea Surface Temperatures
(SSTs) and precipitable water analyses which are currently registering in the
highest climatological percentiles (100th and 84th, respectively) within the
Gulf. Should any surface low develop, there is also the potential for the low
to acquire tropical characteristics during the period.



Upstream, a slight risk of heavy precipitation remains posted over the Four
Corners and into parts of the High Plains. The slight risk is now valid through
Sep 26 based on enhanced precipitable water content that is favored to persist
associated with weakening troughing aloft, and also moisture contributions from
potential TC activity in the Eastern Pacific. The National Hurricane Center
(NHC) continues to monitor an area located to the south of Mexico with 80%
chances of formation during the next week (as of 11am PDT), where ensembles
generally favor the disturbance taking more of a northward track near the Gulf
of California supportive of a surge event later next week. Given the continued
indications of potentially heavy precipitation during the next week or so, a
flooding possible hazard remains posted due within the slight risk area of
heavy precipitation. Week-1 precipitation amounts are forecast to be in excess
of 1-2 inches over many parts of New Mexico. This region is prone to flash
flooding and caution should be exercised near canyons and creek beds.



Underneath the amplified ridge axis favored, above-normal temperatures are
predominately favored with the strongest temperature anomalies featured over
many parts of the Interior West, Great Plains, and Mississippi Valley.  As
reflected in the Probabilistic Extreme Tools (PETs) with increased chances for
maximum daytime temperatures exceeding the 85th percentile, temperatures are
expected to grow warmer during week-2, but no corresponding temperature related
hazards are posted. Actual daytime maximums are expected to remain below hazard
criteria due to decreasing sun angles in the autumn, as the anomalously warm
temperatures are also not anticipated to adversely impact ground conditions.



No hazards are posted across Alaska.  Due to above-normal precipitation
forecast for much of the state, flooding is possible across parts of the
western and central Mainland where many areas have consistently registered
above-normal since this summer. Although the mid-level height pattern is not
particularly amplified over Alaska during week-2, recurving TCs from the
western Pacific may lead to an abrupt amplification of the pattern, which will
be closely monitored for any hazardous impacts.



In addition to the aforementioned watch area for TC development in the eastern
Pacific, the NHC is also monitoring a tropical wave with 80% chances of
development between approximately 115W-140W as of 11am PDT, as well as another
watch area to the west associated with the remnants of Tropical Depression 15
with 20% chances of formation during the next week. Any additional
precipitation related to these disturbances nearing Hawaii may worsen already
saturated grounds, following the impacts associated with TCs Lowell, Moke, and
Lala this season.

FORECASTER: Nick Novella

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