980
FXUS21 KWNC 051922
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 05 2025

SYNOPSIS: Mid-level low pressure across the northeastern Pacific and eastern
Alaska downstream from a narrow but strong mid-level high pressure ridge
centered just west of the Alaska Mainland are expected to entrench 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. After a brief lull at the beginning of week-2, the mid-level low
pressure should enhance moist Pacific flow across the northwestern Contiguous
U.S. (CONUS) with increased chances of heavy precipitation and high winds
redeveloping by the middle of week-2. In the northeastern CONUS, an area of
surface low pressure moving away from the Northeast and cold high pressure
building into the eastern CONUS in its wake increases the odds for high winds
over parts of the Great Lakes, Northeast, central Appalachians, and
Mid-Atlantic. This set-up also enhances the likelihood of heavy lake-effect
snows on the lee side of the Great Lakes.

HAZARDS

Moderate risk of much below normal temperatures for most of Southeast Alaska,
Sat-Mon, Dec 13-15.

Slight risk of much below normal temperatures for much of central, eastern, and
southern AK, Sat-Fri, Dec 13-19.

Moderate risk of high winds across southern Alaska from the eastern Aleutians
through central Southeast Alaska, Sat-Fri, Dec 13-19.

Slight risk of high winds for southern Alaska from the central Aleutians
through Southeast Alaska, Sat-Fri, Dec 13-19.

Slight risk of much below normal temperatures for the Upper Mississippi Valley,
Great Lakes, and Ohio Valley, Sat-Tue, Dec 13-16.

Slight risk of heavy snow across the Upper Peninsula of Michigan, the lee side
of Lakes Michigan, Erie, and Ontario, and the central Appalachians, Sat-Mon,
Dec 13-15.

Slight risk of high winds for the Great Lakes, Northeast, and northern portions
of the mid-Atlantic, Sat-Sun, Dec 13-14.

Slight risk of heavy precipitation across the Pacific Northwest and Northern
California, Mon-Wed, Dec 15-17.

Slight risk of heavy snow across the Cascades and northern Sierra-Nevada
Ranges, Mon-Wed, Dec 15-17.

Slight risk of heavy snow across part of the northern Rockies and adjacent High
Plains, Mon-Wed, Dec 15-17.

Slight risk of high winds for coastal regions of the Pacific Northwest and
Northern California, Mon-Wed, Dec 15-17.

Flooding possible across parts of the Pacific Northwest.

DETAILED SUMMARY

FOR MONDAY DECEMBER 08 - FRIDAY DECEMBER 12:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY DECEMBER 13 - FRIDAY DECEMBER 19: The 0z ECWMF, GEFS, and Canadian
ensembles depict a highly-amplified mid-level ridge centered west of Alaska,
with a fairly 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 that keeps
exceptionally cold air entrenched over much of Alaska. The Probabilistic
Extremes Tools (PETs) from all three ensembles maintain strong chances for
temperatures to fall below the 15th climatological percentile over Southeast
Alaska early in Week-2. The GEFS PET forecasts 60 to 80 percent chances for
temperatures below the 15th percentile from southeastern Mainland Alaska
through the Southeast early in the period. The ECENS PET is less robust again
today, keeping odds for such temperatures in the 40 to 60 percent range over
approximately the same area and reducing those chances earlier in week-2.
Apparent temperatures are forecast to fall to near hazardous criteria in much
of Mainland Alaska and into Southeast.



There is some uncertainty regarding how conditions evolve over the course of
week-2. The ECENS PET rapidly reduces chances for temperatures to fall below
the 15th percentile while the GEFS maintains stronger chances through much of
week-2. The mid-level height pattern appears to deamplify slightly by the
middle of the period with the ECENS favoring a much weaker mid-level trough by
the second half of week-2 over the northeastern Pacific. However, the GEFS
maintains a strong mid-level low and both ensembles maintain surface high
pressure over Mainland Alaska and the Yukon through the period. Given the
consistency in the guidance early in week-2, a moderate risk of much below
normal temperatures is posted for Southeast Alaska for days 8-10. A broader
slight risk extends into much of the eastern, central, and southern parts of
the Mainland where hazardous criteria are significantly higher. Due to the
increased uncertainty by the middle of week-2 a slight risk of much below
normal temperatures is maintained through the end of the period.



Meanwhile, south of the strong surface high pressure covering most of the
state, low surface pressures are favored near the mid-level trough in the
northeastern Pacific. This sets up a pattern that would support gap winds
across much of southern Alaska. The pressure gradient between high pressure
over land and low pressure over sea will wax and wane through the period, but
the pattern favoring high winds across the southern tier of the state should
stay in place throughout week-2. As a result, a moderate risk of high winds is
posted across southern Alaska near the coastline from from the eastern
Aleutians to central portions of Southeast Alaska for the entirety of week-2.
The strongest winds are likely to be in the mountain gaps and models show
episodes of strong winds most consistently affecting this region. A slight risk
of high winds surrounds this region, stretching farther west into the Aleutians
and farther southeast through the entire Alaska Panhandle. 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.



The 0z ECENS, GEFS, and Canadian ensemble means all depict anomalous 500-hPa
troughing moving into the Atlantic through early week-2. This should strengthen
surface low pressure heading away from the Northeast. Meanwhile, cold high
pressure is expected to push into the Great Lakes and eastern CONUS behind the
storm system. The pressure gradient between these two systems may result in
periods of high winds across the Great Lakes, Northeast, and northern
mid-Atlantic, where a slight risk of high winds is posted for the first two
days of week-2. These winds will advect cold air southward from northern Canada
into the region, potentially resulting in low wind chills and heavy lake effect
snow squalls. The PETs from the ECENS and GEFS indicate at least a 20% chance
of temperatures to fall below the 5th percentile, with the ECENS indicating
some areas where there is at least a 20% chance of temperatures falling below
the 2nd percentile. Therefore, a slight risk of much below normal temperatures
is forecast for parts of the Upper Mississippi Valley, Great Lakes, and Ohio
River Valley and adjacent areas. A slight risk of heavy snow is posted for the
first three days of week-2 for the favored lake effect snow belts. As the low
pressure moves further away from the CONUS, the surface high pressure is
expected to slide southeastward and slowly weaken and mid-level heights build
across the central CONUS. This should relax the pressure gradient, ending the
high wind and heavy snow threats by the middle of the period and building
heights will reduce chances for bitterly cold temperatures.



Building mid-level 500-hPa heights across the Rockies and central CONUS during
the middle of week-2, along with mid-level low pressure in the Northeast
Pacific, favor a return of onshore flow into the Pacific Northwest and Northern
California. There remains some uncertainty in the overall evolution of the
mid-level flow pattern and timing but the PETs and Integrated Water Vapor (IVT)
tools favor an increase in onshore flow by around day 10. Therefore, a slight
risk of heavy precipitation is posted for western Washington, Oregon, and
northwestern California for days 10-12. A corresponding slight risk of heavy
snow highlights the higher elevations of the Cascades and northern Sierra
Nevada. And a slight risk of high winds is posted for coastal regions of the
West Coast, north of the San Francisco Bay Area. A flooding possible hazard
remains posted for portions of western Washington and northern Oregon, where
additional precipitation may increase the risk for flooding and landslides as
the soil conditions will remain wet from an atmospheric river in week-1.

FORECASTER: Ryan Bolt

$$