615
FXUS21 KWNC 121808
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 12 2026

SYNOPSIS: A cool air mass is forecast for portions of the Northeast bringing
chances for first frosts and freezes to parts of the region. Another round of
enhanced mid-level moisture is favored to overspread the western and central
CONUS, potentially bringing heavy precipitation and possible flooding over
portions of the Four Corners. In Alaska, a potent area of low pressure is
forecast in the Gulf of Alaska that may bring chances for heavy precipitation
and high winds to portions of the southeastern Mainland and Southeast Alaska.

HAZARDS

Slight risk of much below normal temperatures for parts of northern New
England, Sun-Tue, Sep 20-22.

Slight risk of heavy precipitation for the Four Corners region, Sun-Tue, Sep
20-22.

Slight risk of heavy precipitation for parts of Southeast Alaska and
southeastern Mainland Alaska, Sun-Mon, Sep 20-21.

Slight risk of high winds for parts of Southeast Alaska and southeastern
Mainland Alaska, Sun-Mon, Sep 20-21.

Flooding possible for portions of the Desert Southwest, Great Basin, and
Rockies.

DETAILED SUMMARY

FOR TUESDAY SEPTEMBER 15 - SATURDAY SEPTEMBER 19:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SUNDAY SEPTEMBER 20 - SATURDAY SEPTEMBER 26: The GEFS, ECENS and CMCE
remain in good agreement in regards to the evolution of the 500-hPa pattern
next week. A mid-level ridge amplifies over central and eastern Canada during
week-2 bringing positive height anomalies back to the central and eastern
contiguous U.S. (CONUS) with time. A longwave trough is forecast upstream over
the Gulf of Alaska. Much of the enhanced subtropical ridging that has been
established for quite some time is expected to ease resulting in cooler and
drier conditions for many areas east of the Rockies.



Tied to a transient trough progressing through the northeastern CONUS, a slight
risk of much below normal temperatures remains posted for northern New England
valid for Sep 20-22. Within the highlighted areas, there continues to be
agreement in uncalibrated temperature tools showing increased chances for
temperatures falling below 40 deg F, with the ECENS Probabilistic Extremes Tool
(PET) favoring 20-30% chances of minimum temperatures falling below the 15th
climatological percentile. While near freezing temperatures are not markedly
unusual for this time of year (climatological first freezes occur by late
September for the highlighted areas), any frost and/or freezes associated with
the favored cold air mass may be impactful to some vegetation.



Much of the CONUS remains favored to see above normal temperatures during
week-2 and the GEFS PET maintains increased chances for temperatures remaining
above the 85th percentile much of the country, however chances of extreme heat
are diminished based declining climatologies and on lower heat index values
indicated by the tools by the start of week-2, thus no corresponding hazard
areas are posted. Continued above-normal temperatures may exacerbate dry ground
conditions and sustain an increased wildfire risk, but given the relatively
cooler temperatures favored and decreasing sun angles with the start of autumn
soon approaching, the prospect of additional impacts associated with the
persistent warmth is lower overall. Some model guidance continues to bring
elevated chances for heavy precipitation to parts of the southeastern CONUS. A
lingering frontal zone is forecast across the region and southerly return flow
could bring elevated tropical moisture into the region. Uncertainty remains too
high to post a precipitation hazard at this time; this area will continue to be
monitored.



Weak troughing and onshore flow favored near the West Coast along with the
potential for additional tropical moisture from the eastern Pacific, a slight
risk of heavy precipitation remains posted (Sep 20-22) over the Four Corners
where uncalibrated tools maintain elevated chances for 3-day precipitation
amounts exceeding a half an inch, and in some locations more than one inch. In
addition, given the continued indications of potentially heavy precipitation
during the next week or so, a possible flooding hazard remains posted for
portions of the Four Corners. This region is prone to flash flooding and
caution should be exercised near canyons and creek beds, and additional
rainfall may hamper recovery efforts from recent flooding in the Grand Canyon.



Multiple model ensembles depict surface and mid-level low pressure over the
Gulf of Alaska resulting in enhanced onshore flow and the potential for heavy
precipitation and high winds along portions of the southern and southeastern
coast of Alaska. The model guidance indicates the potential for 3-day
precipitation totals to approach hazardous criteria with widespread strong
probabilities of 3 day precipitation amounts exceeding 2 inches and isolated
areas of more than 3 inches throughout much of southeastern Alaska.
Correspondingly, PETs indicate elevated chances for winds to exceed the 85th
climatological percentile and 40mph near the coast. Therefore, a slight risk of
heavy precipitation is posted from the Kenai Peninsula through all of Southeast
Alaska for Sep 20-21 and a corresponding slight risk of high winds is posted
from Prince William Sound through Southeast Alaska for the same period.



Across the eastern Pacific, the National Hurricane Center (NHC) is currently
monitoring TC Norbert, as well as a pair of watch areas located near 150W and
115W with 10% and 90% chances of development, respectively, during the next
week. While the latter higher likelihood area looks to be more of a factor in
regards to the enhancing moisture advection into the CONUS, a continued
westward track from Norbert beyond the official forecast track from NHC, as
well as the lower likelihood watch area in proximity to Hawaii may pose an
additional heavy precipitation threat to the state during the next few weeks.
Any additional TC related precipitation may worsen already saturated grounds
across parts of Hawaii, as there has not been much time for recovery following
the impacts associated with TCs Lowell, Moke, and Lala this season.

FORECASTER: Ryan Bolt

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