431
FXUS21 KWNC 261906
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 26 2025

SYNOPSIS: Mid-level low pressure over southeastern Canada favors a renewed
period of unseasonably cold minimum temperatures, with increased chances for
locally heavy lake effect snowfall over many parts of the northeastern
contiguous U.S. (CONUS) later next week.  Developing mid-level low pressure
across western CONUS  increases the likelihood for heavy precipitation over
California and the Southwest, with the potential for high elevation heavy
snowfall across Interior West.  Lingering frontal activity across the southern
tier of the U.S. may trigger heavy precipitation over portions of the Gulf
states early in week-2.

HAZARDS

Slight risk of much below normal temperatures for much of the north-central and
northeastern CONUS, Thu-Sat, Dec 4-6.

Slight risk of heavy snow for parts of the Upper Mississippi Valley, Great
Lakes, and the Northeast, Thu-Sat, Dec 4-6.

Slight risk of heavy precipitation for portions of the Lower Mississippi and
Tennessee Valleys, and the Southeast, Thu-Sat, Dec 4-6.

Slight risk of heavy snow across the Rockies, Great Basin, and the Northern
Intermountain, Thu-Sun, Dec 4-7.

Slight risk of heavy precipitation for portions of California and the Desert
Southwest, Thu-Fri, Dec 4-5.

DETAILED SUMMARY

FOR SATURDAY NOVEMBER 29 - WEDNESDAY DECEMBER 03:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY DECEMBER 04 - WEDNESDAY DECEMBER 10: Towards the middle of next
week, dynamical model height forecasts continue to feature  shortwave energy
shifting across the northeastern CONUS, which looks to bring another round of
anomalously cold air into this part of the country early in week-2. Relative to
yesterday, the ECMWF ensemble has toned back its surface response associated
with the anomalous mid-level troughing, consisting of a weaker mean surface
high pressure center and less impressive negative temperature anomalies
overspreading the eastern U.S.  Still, predominately northwesterly flow remains
favored to help advect anomalously cold air into the northeastern CONUS, and
the latest Probabilistic Extreme Tools (PET) guidance continues to indicate
elevated (20-40%) chances for minimum temperatures falling below the 10th
percentile. Therefore, a slight risk of much below normal temperatures remains
posted for Dec 4-6 and its coverage more focused over the Great Lakes and the
Northeast where deterministic solutions favor apparent temperatures falling
well below 0 degrees F.



With the cold air mass established, accumulating snowfall appears likely, with
Lake Effect snowfall being of particular concern. Although Great Lake
temperatures have cooled this past month, temperatures currently remain above
freezing in the 40s (degrees) conducive for locally heavy accumulations. This
continues to be well supported in the raw ECMWF snow guidance, which continues
to show pockets of elevated chances for snowfall amounts exceeding 6 inches
downwind of the Lakes, and a slight risk of heavy snow remains issued for Dec
4-6. Based on a few deterministic solutions, accumulating snowfall is also
possible further south of the slight risk area over parts of the Appalachians
and northern Mid-Atlantic, though there is not enough ensemble support to
warrant inclusion of these areas in the outlook.



Following a frontal system which is forecast to bring potentially heavy
precipitation amounts from the Southern Plains to the Southeast late in week-1,
both the ECMWF and GEFS ensembles show the return of increased, and potentially
heavy precipitation amounts over portions of the Gulf states on the backside of
the mean surface high pressure center to the east. While the GEFS PET is weak
with the heavy precipitation risk, the ECMWF PET and uncalibrated tools among
the models are in agreement indicating at least 20% chances for 3-day amounts
exceeding an inch over the Lower Mississippi Valley and the parts of the
Southeast to support a slight risk of heavy precipitation (Dec 4-6). Even with
the potential for additional heavy precipitation over portions of the
southeastern CONUS following a wet week-1, the flooding possible hazard is
discontinued as flooding responses from water models have become more isolated
while trending drier.



Across the western CONUS, much of the anomalous troughing favored next week is
expected to pinch off from the longwave trough axis over southeastern Canada,
and settle offshore off of the West Coast to bring a period of unsettled
weather for many parts of the southwestern CONUS. Since yesterday, the ECMWF
has backed off on this feature becoming fully cutoff, resulting in lesser
precipitation amounts in the uncalibrated tools. However, both the GEFS and
ECMWF PETs still indicate increased chances (20-40%) for 3-day amounts
exceeding the 85th percentile and 0.5 inches over the climatologically drier
areas of southern California and the Desert Southwest to support the
continuation of a slight risk of heavy precipitation, valid through Dec 5
before the troughing deamplifies. Due to decreased precipitation and snow
signals further inland, the accompanying slight risk of high elevation heavy
snow is discontinued in the updated outlook.



As the period progresses, ensembles continue to advertise the retrogression of
the amplified mean ridging over the Aleutians, allowing for more troughing to
develop downstream over western North America. The ECMWF ensemble favors more
troughing to dig farther southward along the West Coast, whereas the latest
GEFS now favors more a zonal pattern, reducing chances for enhanced onshore
flow. This discrepancy is reflected in both the ECMWF and GEFS PETs, with the
latter favoring much drier conditions from Central California northward to the
Pacific Northwest during the back half of week-2 compared to yesterday.
Therefore, the  slight risks of heavy precipitation and high elevation heavy
snow are removed in the updated outlook, but this potential will be revisited
in the coming days.



The predicted troughing favored across the Interior West supports the
continuation of a slight risk of heavy snow remaining issued over the higher
elevations of the Rockies, Great Basin and Northern Intermountain. Though, due
to the lack of anomalous troughing in the GEFS, and reduced signals in the GEFS
Snow Water Equivalent (SWE) towards the middle of period,  this slight risk
area is now valid through Dec 7.  PET Periods of high winds are possible at the
base and ahead the mean troughing across the West, however tools remain
unsupportive of a corresponding wind hazard.



Over Alaska, the aforementioned mid-level pattern shift towards the middle part
of week-2 is favored to lead to a fairly swift transition from above to below
normal temperatures, increasing concerns of extreme cold conditions developing
over eastern Mainland Alaska. No corresponding temperature hazards are issued
as PETs remain rather muted with the cold signals over the Mainland, but this
potential will continue to be monitored.

FORECASTER: Nick Novella

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