628
FXUS21 KWNC 251924
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 25 2025

SYNOPSIS: Renewed mid-level low pressure favors unseasonably cold minimum
temperatures for many parts of the northeastern contiguous U.S. (CONUS) later
next week, along with the potential for locally heavy lake effect snowfall.
Developing mid-level low pressure across western North America increases the
likelihood for heavy precipitation and high elevation snowfall across the West
Coast and Interior West, with this threat shifting northward later in week-2.
Predicted frontal forcing is expected to bring a lingering risk of heavy
precipitation across the southeastern CONUS early in week-2, with possible
flooding across portions of the Ohio and Tennessee Valleys.

HAZARDS

Slight risk of much below normal temperatures for much of the north-central and
northeastern CONUS, Wed-Sat, Dec 3-6.

Slight risk of heavy snow for parts of the Upper Mississippi Valley, Great
Lakes, and the Northeast, Wed-Sat, Dec 3-6.

Slight risk of heavy precipitation for portions of the Lower and Middle
Mississippi Valley, the Tennessee and Ohio Valleys, Appalachians, and
Southeast, Wed, Dec 3.

Slight risk of heavy snow across the Rockies, Great Basin, and the Northern
Intermountain, Wed-Tue, Dec 3-9.

Slight risk of heavy precipitation for portions of California and the Desert
Southwest, Wed-Sat, Dec 3-6.

Slight risk of heavy snow for portions of the southern Sierra Nevada mountains,
Wed-Sat, Dec 3-6.

Slight risk of heavy precipitation for portions of northern California and the
Pacific Northwest, Sat-Tue, Dec 6-9.

Slight risk of heavy snow for the higher elevations of the Cascades, Klamath,
and northern Sierra Nevada mountains, Sat-Tue, Dec 6-9.

Flooding possible for the Tennessee and Ohio Valleys.

DETAILED SUMMARY

FOR FRIDAY NOVEMBER 28 - TUESDAY DECEMBER 02:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY DECEMBER 03 - TUESDAY DECEMBER 09: Dynamical models continue to
advertise a highly amplified 500-hPa pattern in the higher latitudes over North
America consisting of a potent ridge over the northeastern Pacific and
extending northward into the Bering Sea, with a strong negative mean height
anomaly field over southeastern Canada during the week-2 period. With a mean
trough axis extending into the southwestern CONUS and into northern Mexico,
this pattern remains favorable for the intrusion of Arctic air from Canada
while increasing the risk of other weather related hazards across the CONUS.
Later in week-2, models have been trending towards retrograding the mid-level
ridge over the Bering Strait, allowing for more anomalous troughing to develop
over southwestern Canada and the Pacific Northwest. Such a shift would become
more favorable for a transition to cooler and drier conditions across Alaska,
but increase the potential for enhanced onshore flow and above-normal
precipitation across portions of the West Coast later in week-2.



Consistent with previous ensemble guidance, both the GEFS and ECMWF continue to
indicate the additional shortwave energy propagating along the mean trough axis
across the Interior West, which looks to trigger another outbreak of
anomalously cold air into the Midwest towards the later part of next week. The
potential for renewed cold comes on the heels of a cold air intrusion initially
favored late in week-1, where some moderation of temperatures is expected east
of Rockies heading into early week-2 based on the daily raw temperature tools.
These tools also feature the greatest reinforcement of negative temperature
departures over the northeastern CONUS by days 9 and 10 (Dec 4-5), with the
GEFS being weakest with this potential compared to the ECMWF and Canadian.
Given the reduced potential for anomalous cold returning over the lower
latitudes of the U.S, the slight right of much below normal temperatures is
discontinued over Texas. However, a corresponding slight risk area remains
issued over the northern portions of the Plains and Mississippi Valley, with
coverage expanded eastward to include the Great Lakes and the Northeast in the
updated outlook (Dec 3-6). Within the highlighted area, Probabilistic Extremes
Tools (PETs) show elevated (20-40%) chances for nighttime minimum temperatures
falling below the 10th percentile, with the deterministic ECMWF indicating
apparent temperatures dipping into -10s and -20s (degrees F) to reach winter
hazards criteria over some locations.



With an anomalously cold air mass favored to be established over the
northeastern CONUS, the prevailing northwesterly flow accompanied with
increased tropospheric moisture is expected to remain conducive for
accumulating snowfall, where Lake Effect snowfall is of particular concern.
Although Great Lake temperatures have cooled this past month, temperatures
currently remain above freezing in the 40s (degrees) supportive for locally
heavy accumulations. A moderate risk of heavy snow was considered for
inclusion, however due to lesser support in the GEFS based Snow Water
Equivalent (SWE) PET, a broad slight risk area remains posted for Dec 3-6.
Based on some 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 support in the ensembles to
warrant inclusion of these areas in the outlook.



Across the southeastern CONUS, frontal forcing associated with the initial cold
air mass late in week-1 is expected to persist into early week-2, and bring
enhanced precipitation amounts to portions of the Southeast and the eastern
U.S. Based on raw precipitation tools, the heaviest precipitation amounts are
expected late in week-1, though these tools, as well as the PETs indicate the
heavy precipitation risk to potentially linger. Therefore, the moderate risk of
heavy precipitation is removed, and a corresponding slight risk remains posted,
and is now valid for Dec 3 for parts of the Mississippi, Tennessee, and Ohio
Valleys, with added coverage over the Appalachians, Southeast and Mid-Atlantic
in the updated outlook. Any continued heavy precipitation over portions of the
Ohio and Tennessee Valleys may trigger isolated flooding where a flooding
possible hazard remains posted.



Tied to the mean troughing across the western CONUS that is favored to persist
throughout the period, raw snow tools and the GEFS SWE PET remain supportive of
a slight risk of heavy snow remaining issued over the higher elevations of the
Rockies, Great Basin and Northern Intermountain, now valid for the entirety of
week-2. Periods of high winds are possible at the base and ahead the mean
troughing axis across the West, however tools are not quite supportive of a
corresponding wind hazard at this time.



As the mean negative height departures have trended westward in the ensembles,
a new key development in mid-level height guidance is the potential for cutoff
low formation off of southern California early in week-2, which is most
pronounced in the ECWMF ensemble. As a result, the precipitation response is
particularly strong across portions of California and the Desert Southwest in
the ECMWF PET, indicating 40-60% chances for 3-day precipitation amounts
exceeding the 85th percentile. Caution is exercised given a drier climatology,
and the tendency for the ECMWF PET to overforecast precipitation risks over
this part of the country. However, due to the GEFS trending in a wetter
direction since yesterday, a slight risk of heavy precipitation is posted for
over portions of central and southern California, and into the Desert Southwest
for Dec 3-6. With this area, a corresponding heavy snow hazard is issued over
the higher elevations of the southern Sierra Nevada mountains for the same
period. Increased precipitation amounts are also indicated further north across
northern California and the Pacific Northwest associated with the
aforementioned shift in the height pattern during the back half of week-2.
Although uncertainty is high at this longer lead, there is good agreement
between the raw guidance and calibrated GEFS and ECMWF PETs to support the
addition of a slight risk of heavy precipitation, as well as an accompanying
slight risk of high elevation heavy snowfall for the Cascades, Klamath, and
portions of the Sierra Nevada mountains for Dec 6-9. The return of enhanced
onshore flow over the northern half of the West Coast is also supported by
Integrated Vapor Transport (IVT) tools, which show increased chances for values
exceeding 250 kg/m/s beyond day 11 (Dec 6).



Mean surface low pressure favored in the Gulf of Alaska is expected to bring
above-normal precipitation and periods of elevated wind speeds for parts of the
Mainland and the Southeast early in week-2, though totals are not expected to
reach hazard thresholds. During the middle to latter part of week-2, a
transition from warm to much cooler temperatures are favored associated with
the 500-hPa ridge shifting eastward, which may lead to extreme cold conditions
developing over eastern Mainland Alaska. No hazards are issued at this time,
but this potential will continue to be monitored in upcoming outlooks.

FORECASTER: Nick Novella

$$