229
FXUS21 KWNC 161825
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 16 2026

SYNOPSIS: Mid-level low pressure situated offshore of the West Coast, as well
as lingering frontal activity and potential surface low development near the
Eastern Seaboard supports an increased risk of heavy precipitation over the
parts of the Four Corners, eastern Great Plains, and the eastern 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 Mid-Atlantic and
Southeast, Thu-Mon, Sep 24-28.

Slight risk of heavy precipitation for parts of the Southwest, southern
Rockies, and Southern High Plains, Thu-Fri, Sep 24-25.

Flooding possible for portions of the Four Corners region.

DETAILED SUMMARY

FOR SATURDAY SEPTEMBER 19 - WEDNESDAY SEPTEMBER 23:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY SEPTEMBER 24 - WEDNESDAY SEPTEMBER 30: Consistent with previous
ensemble based guidance, there continues to be disagreement between the GEFS
and ECMWF 500-hPa mean height forecasts towards the middle of next week. While
the ECMWF has become somewhat better aligned with the GEFS in regards to the
development of rising heights across the northwestern CONUS to promote more
cutoff troughing situated offshore of the West Coast late in week-1, the GEFS
continues to feature the progression of a mean trough across the upper Midwest
and into the Northeast, which is virtually absent in the ECMWF and Canadian
early in week-2. Instead, a more potent and expansive anomalous ridge feature
centered to the south of Hudson Bay is favored in these models, resulting in a
different surface reflection compared to the GEFS for much of the eastern CONUS
later next week. Notwithstanding, either lingering or renewed frontal activity
remains favored across the southeastern CONUS, and combined with the
aforementioned troughing favored upstream, there continues to be an increased
risk of heavy precipitation for the Four Corners and the eastern Seaboard in
the updated outlook. Later in week-2, both the GEFS and ECMWF become somewhat
better aligned in favoring a stable pattern, consisting of amplified ridging
centered throughout much of central North America, bookended by a pair of mean
troughs over the western and eastern CONUS.



In response to the anomalous ridging centered over southcentral Canada,
above-normal temperatures are predominately favored mainly east of the Rockies,
with the strongest temperature anomalies featured over the southeastern and
throughout the north-central CONUS in proximity to the ridge. Even with
temperatures continuing to grow warmer later next week, no corresponding
temperature related hazards are posted as actual daytime maximums are expected
to remain below hazard criteria due to decreasing sun angles in the autumn,
with not much impact expected on ground conditions.



Across the eastern CONUS, a slight risk of heavy precipitation remains posted
for much of the eastern Seaboard, where models continue to point to frontal
activity with the GEFS favoring more cyclonic surface flow supportive of
offshore low development. Relative to yesterday, the coverage of the slight
risk area has been removed (added) over the Northeast (coastal Southeast), and
extended through Sep 28 based on trends in the tools. While the highest
precipitation amounts are more likely offshore, Probabilistic Extreme Tools
(PETs) continue to feature increased chances for 3-day amounts exceeding the
85th percentile and 1 inch early in the period, where spatially, both PETs and
raw tools continue to show a connection to the tropics to help supply deeper
moisture. This 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, which is reflected in the latest Global Tropics Hazards (GTH) outlook,
with 20% chances of Topical Cyclone (TC) formation issued to the north of the
Bahamas in the western Atlantic.



Tied to the troughing favored off the West Coast, a slight risk of heavy
precipitation remains posted over the Four Corners and into the High Plains,
and is now valid through Sep 25 based on a persistence of moisture signals in
the guidance. The slight risk area captures variations in the heavy
precipitation potential in the raw tools, with the GEFS (ECMWF) favoring a more
westward (eastward) focused solution of the risk in the updated guidance. Even
with these differences, both PETs feature increased chances of 3-day amounts
exceeding the 85th percentile and a half an inch early in week-2. Given the
continued indications of potentially heavy precipitation during the next week
or so, a flooding possible hazard remains posted with added coverage over parts
of southern Utah based on increased chances of excessive rainfall possible
during the next week. Within the highlighted area, week-1 precipitation amounts
are forecast to be in excess of 1-2 inches over parts of Arizona and New
Mexico. This region is prone to flash flooding and caution should be exercised
near canyons and creek beds.



Across Alaska, ensembles show mid-level troughing becoming much less amplified
heading into week-2 to quell any precipitation and wind related hazard risks
over Alaska, and no hazards are posted. However, the high latitude pattern will
continue to be closely monitored in the models due to recurving TCs in the
western Pacific, which could abruptly lead to a reamplification of the
troughing aloft and associated surface low development. It is worth noting that
parts of the western and central Mainland have been anomalously wet, where a
continuation of above-normal precipitation may possibly lead to localized
flooding.



In the Pacific, the National Hurricane Center (NHC) is currently monitoring
three areas for potential TC development, with one located approximately
between 120W-140W. There are 40% chances of formation associated with this
tropical wave, with support in both the ECMWF and Google AI solutions favoring
a continued westward track into the Central Pacific later next week. Any
additional precipitation related to this disturbance over 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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