742
FXUS21 KWNC 012000
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 01 2025

SYNOPSIS: Mid-level low pressure forecast across the northeastern Pacific and
Alaska combined with amplifying mid-level high pressure further south along the
West Coast of the contiguous U.S. (CONUS) favors enhanced onshore flow across
the northwestern CONUS extending through southeastern Alaska during week-2.
Dynamical models depict a short-duration burst of heavy precipitation early in
the period across parts of the Pacific Northwest, with heavy snow likely across
high elevation areas of the Cascades and northern Rockies. Mid-level low
pressure also remains forecast across the eastern U.S. at least into the second
week of December resulting in continued increased storminess and cold
temperatures over portions of the Great Lakes and Northeast.

HAZARDS

Moderate risk of heavy precipitation across western Washington and northwestern
Oregon, Tue-Wed, Dec 9-10.

Slight risk of heavy precipitation across portions of the Pacific Northwest and
far northwestern California, Tue-Thu, Dec 9-11.

Moderate risk of heavy snow across the northern Cascades, Tue-Wed, Dec 9-10.

Slight risk of heavy snow across the Cascades, Tue-Thu, Dec 9-11.

Slight risk of heavy snow across the northern Rockies, Tue-Thu, Dec 9-11.

Slight risk of heavy snow across the Upper Peninsula of Michigan and western
portions of Lower Michigan, Tue-Wed, Dec 9-10.

Slight risk of heavy snow across portions of the interior Northeast and
Mid-Atlantic, and Central Appalachians, Tue-Wed, Dec 9-10.

Moderate risk of high winds across portions of the Pacific Northwest, northern
Great Basin, northern and central Rockies, and northern and central High
Plains, Tue-Wed, Dec 9-10.

Slight risk of high winds across the northwestern CONUS into the northern and
central High Plains, Tue-Thu, Dec 9-11.

Slight risk of much below normal temperatures across portions of Upstate New
York and northern New England, Tue-Wed, Dec 9-10.

Slight risk of much below normal temperatures across portions of southern
Mainland Alaska and the Alaska Peninsula, Tue-Thu, Dec 9-11.

Slight risk of high winds across southeastern Alaska, Tue-Mon, Dec 9-15.

Flooding possible across the Pacific Northwest.

DETAILED SUMMARY

FOR THURSDAY DECEMBER 04 - MONDAY DECEMBER 08:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY DECEMBER 09 - MONDAY DECEMBER 15: The 0z ECWMF, GEFS, and Canadian
ensembles all depict anomalous 500-hPa troughing across the East during week-1
and into week-2. As a result, several shortwave impulses are forecast to
traverse the CONUS favoring an active weather pattern across the East. The
interaction between the southern and northern streams will ultimately determine
the placement of wintry weather, with the potential for a system moving through
every couple of days. This progression of shortwaves supports maintaining a
slight risk of heavy snow across portions of the Great Lakes, interior
Northeast, and extending along the Allegheny Front, Dec 9-10, with heavy snow
either directly from the individual systems or Lake Effect.



Along with the potential for snow, is the possibility of much below-normal
temperatures. The ECMWF Probabilistic Extremes Tool (PET) depicts parts of the
Northeast having at least a 50 percent chance minimum temperatures fall below
the 10th climatological percentile. This would correspond to elevated chances
of subzero temperatures over portions of Upstate New York and northern New
England, with negative teens possible closer to the Canadian Border. Taking
wind chill into account, some of these areas may reach NWS Cold Advisory
criteria supporting a slight risk for much below normal temperatures, Dec 9-10.
While the GEFS PET depicts weaker probabilities for hazardous cold compared to
the ECMWF, today`s run is notably more persistent with troughing over the
Northeast compared to yesterday. However, the overall mid-level pattern
evolution remains uncertain beginning in the middle of week-2 with mixed
signals in the dynamical models regarding the mid-level pattern across the
CONUS and the placement of amplified features. Given the uncertainty, no
hazards are posted across the East beyond day-9 (Dec 10).



The 0z ECWMF, GEFS, and Canadian ensembles depict an amplified trough-ridge
dipole over Alaska and the southwestern CONUS respectively early in the week-2
period. This set-up favors strong onshore flow, and subsequently, rounds of
heavy precipitation into western North America. All of the models depict
24-hour precipitation totals upwards of 1 to 1.5 inches over the Pacific
Northwest on day-8 (Dec 9). The GEFS and ECMWF-based Integrated Vapor Transport
(IVT) tools depict high probabilities (greater than 80 percent) for IVT values
to exceed 250 kg/m/s, with even a signal for exceeding 500 kg/m/s. While this
appears to be a short-duration event, with lessening precipitation totals by
day-10 (Dec 11), the strong signals in the models and IVT tools support the
addition of a moderate risk of heavy precipitation across the Pacific
Northwest, Dec 9-10. Because of heavy antecedent precipitation forecast in
week-1, any additional precipitation is likely to contribute to flooding along
with potential landslides across the Pacific Northwest, prompting the inclusion
of a flooding possible hazard. In addition to the precipitation, a moderate
risk of heavy snow is posted across the Northern Cascades where 24-hour totals
may exceed 1-foot based on the uncalibrated GEFS and ECMWF ensembles.



A slight risk of heavy precipitation is posted across the Pacific Northwest
into far northwestern California, Dec 9-11. Accompanying slight risks of heavy
snow are posted across the Cascades and northern Rockies for the same time
frame. A moderate risk for heavy snow was considered across the Northern
Rockies, but snow totals are not as high in the uncalibrated models compared to
the northern Cascades. A moderate risk for high winds is posted across the
northwestern CONUS into the northern and central High Plains where both the
GEFS and ECMWF PETs depict at least a 30 percent chance wind speeds exceed the
85th climatological percentile with a strong surface pressure gradient into the
Northwest depicted in the ensemble guidance. This favors wind speeds above
25-mph, possibly above 40-mph along the coast, increasing the risk of coastal
erosion and flooding, along with blizzard conditions for higher elevation areas
that receive snow. A broader slight risk for high winds is highlighted through
Dec 11.



Below-normal temperatures are likely across Alaska associated with troughing
over the state. The GEFS and ECMWF PETs indicate at least a 20 percent chance
minimum temperatures fall below the 15th climatological percentile over some
areas, with higher probabilities in the GEFS (ECMWF) focused more to the east
(southwest). Despite this mismatch, there is good agreement regarding the
potential for temperatures to fall below -20 deg F across interior southern
Alaska, and possibly below 0 deg F closer to the coast, which would be
considerably cold for this time of year. Therefore a slight risk for much below
normal temperatures is posted across southern Mainland Alaska and the Alaska
Peninsula, Dec 9-11. Periods of heavy precipitation and high winds are likely
across Southeast Alaska due to enhanced onshore flow. While precipitation
totals in the PETs and uncalibrated guidance do not reach hazards thresholds,
the ECMWF PET depicts parts of the region having at least a 20 percent chance
wind speeds exceed 40-mph associated with mean surface low pressure over the
Gulf of Alaska. Therefore, a slight risk for high winds is posted across
southeastern Alaska for all of week-2.

FORECASTER: Thomas Collow

$$