488
FXUS21 KWNC 082100
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 08 2025

SYNOPSIS: Mid-level low pressure across the northeastern Pacific and eastern
Alaska downstream from a strong mid-level high pressure ridge centered just
west of the Alaska Mainland are forecast to bring very cold air and dangerous
wind chills across central and southern Alaska, along with episodes of high
winds across southern Alaska from the Aleutians into Southeast Alaska. Enhanced
onshore flow into the northwestern contiguous U.S. (CONUS) is forecast to
persist from week-1 into week-2 with mid-level low and high pressure to the
north and south of the region, respectively. An Arctic air mass is forecast to
move south of the Canadian border into the north-central CONUS, before
progressing rapidly eastward across the Great Lakes and Northeast. For much of
the East however, increased return flow from the Gulf is expected to moderate
temperatures.

HAZARDS

Moderate risk of high winds across southern Alaska from the eastern Aleutians
through central Southeast Alaska, Tue-Mon, Dec 16-22.

Slight risk of high winds for southern Alaska from the central Aleutians
through Southeast Alaska, Tue-Mon, Dec 16-22.

Moderate risk of much below normal temperatures for most of Southeast Alaska,
Tue-Thu, Dec 16-18.

Slight risk of much below normal temperatures for much of central, eastern, and
southern Alaska, Tue-Thu, Dec 16-18.

Moderate risk of heavy precipitation for portions of the Pacific Northwest,
Tue-Thu, Dec 16-18.

Slight risk of heavy precipitation for portions of the Pacific Northwest and
Northern California, Tue-Sun, Dec 16-21.

Moderate risk of heavy snow across the Northern Cascades, Tue-Thu, Dec 16-18.

Slight risk of heavy snow across the Cascades, northern Sierra Nevada and
Klamath Ranges, Tue-Sun, Dec 16-21.

Slight risk of heavy snow across part of the northern Rockies and adjacent High
Plains, Tue-Sun, Dec 16-21.

Moderate risk of high winds for portions of the Pacific Northwest, Tue-Thu, Dec
16-18.

Slight risk of high winds for portions of the Pacific Northwest and northern
California, Tue-Sun, Dec 16-21.

Slight risk of much below normal temperatures for portions of the north-central
states, Thu-Sat, Dec 18-20.

Flooding possible across parts of the Pacific Northwest.

DETAILED SUMMARY

FOR THURSDAY DECEMBER 11 - MONDAY DECEMBER 15:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY DECEMBER 16 - MONDAY DECEMBER 22: The 0z ECWMF, GEFS, and Canadian
ensembles depict a highly-amplified mid-level ridge centered west of Alaska,
with an amplified downstream mid-level trough established over southeastern
Alaska and the adjacent northeastern Pacific. This set-up favors persistent
surface high pressure across much of Alaska and the Yukon throughout week-2.
Conversely, mean low pressure is favored in the Gulf of Alaska. The pressure
gradient between these features brings increased chances for episodes of high
winds across much of southern Alaska between the eastern Aleutian Islands
through much of Southeast Alaska. High winds would be particularly favored in
gaps and inlets. Probabilistic Extremes Tools (PETs) show enhanced chances of
wind speeds exceeding the 85th climatological percentile. Therefore, broad
moderate and slight risks of high winds are posted for all of week-2 for much
of southern Alaska.



PETs continue to highlight enhanced chances for temperatures to fall to near
hazardous thresholds across Southeast Alaska and into the southeastern
Mainland. However, chances for hazardous much below normal temperatures are
reduced by the middle of week-2 and further reduced by the end of the period.
This is tied to the mid-level height pattern deamplifying over Alaska through
the period resulting in less northerly flow into the state. A moderate risk is
posted for Southeast Alaska for Dec 16-18, while a broader slight risk is
maintained for much of the interior, south-central, and Southeast Alaska for
the same period. The combination of very cold weather and high winds along the
southern tier of the state increases the threat for heavy freezing spray at
times near larger bodies of water.



Temperatures across the East are expected to moderate as the week-2 period
progresses, coincident with a predicted rapid flattening of the 500-hPa flow
pattern and the migration of surface high pressure off the Southeast coast.
This favors increasing return flow from the Gulf of America, with precipitation
overspreading much of the Lower Mississippi and Tennessee Valleys early in the
period. The wetter ECENS PET depicts nearly an inch of precipitation during the
first few days of week-2, while the drier GEFS PET favors about three-quarters
of an inch. For now, this situation is only mentioned in the text discussion,
and no hazardous precipitation area has been designated. Towards the middle of
the forecast period, a shallow undercutting Arctic air mass is depicted by the
models to rapidly progress south of the Canadian border into Montana, the
Dakotas, and the Upper Mississippi Valley. Thereafter, this air mass is
predicted to be escorted rapidly eastward across the Great Lakes and Northeast
by fast westerlies, with little additional southward penetration. Accordingly,
a slight risk of much below-normal temperatures is indicated over portions of
the north-central CONUS, Dec 18-20.



A mid-level ridge extending from off the California coast east-northeastward
into the Four Corners region coincident with a mid-level trough over Southeast
Alaska will result in a significantly enhanced onshore flow pattern for the
Pacific Northwest and Northern California. PETs and IVT guidance provide
increasingly clear signs of an atmospheric river taking shape sometime late in
week-1 and continuing throughout most, if not all of, week-2. The ECENS
precipitation guidance is more robust compared to the GEFS counterparts, with a
widespread area of 2 inches favored across much of the Pacific Northwest and
the coast of at least Northern California, with uncertainty in how far south
this feature may extend into Central California. For now, a moderate risk of
heavy precipitation is posted for western portions of Washington and Oregon,
Dec 16-18, with a slight risk area that continues south to near the San
Francisco Bay area, Dec 16-21. As this moisture streams farther inland, heavy
mountain snow is expected to fall across the Cascades, Klamath, and Northern
Sierra Ranges. A moderate risk of heavy snow is posted based on the
uncalibrated ECENS tool indicating elevated chances for snowfall exceeding a
foot for the Northern Cascades, Dec 16-18. A broader slight risk area
designated from the Northern Cascades to the Northern Sierras, along with a
separate slight risk for heavy snow is also posted for the vicinity of the
Northern Rockies, both valid for Dec 16-21. An increased pressure gradient
across the Pacific Northwest and Northern California (resulting from high
pressure predicted to the south and low pressure to the north) warrants a
moderate risk of high winds for the Pacific Northwest, Dec 16-18, and a slight
risk of high winds continuing south to include Northern California, Dec 16-21.
PETs indicate wind speeds in excess of the 85th climatological percentile and
at least 20-25 mph. These wind speeds will be reassessed tomorrow, along with
the increasing potential for a significant atmospheric river later in week-1
and much of week-2.



Finally, a flooding possible hazard remains posted for portions of western
Washington and northern Oregon, where any additional precipitation may increase
the risk for flooding and landslides (especially in areas of steep terrain) as
the soil conditions will remain wet from an atmospheric river in week-1.

FORECASTER: Anthony Artusa

$$