633
FXUS21 KWNC 281920
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 28 2025

SYNOPSIS: At the outset of week-2, mid-level low pressure remains forecast
across western North America favoring continued enhanced onshore flow and
increased chances of heavy precipitation (coastal rain and high elevation snow)
for the west coast of the contiguous U.S. (CONUS). Uncertainty increases later
in the period as dynamical models indicate a trend toward increased mid-level
low (high) pressure across the central Pacific (western CONUS). This could
result in a drying trend across the West Coast toward the end of week-2 as well
as moderating temperatures across Alaska. While the pattern across the eastern
U.S. is forecast to be more variable, increasing high latitude blocking
combined with incoming shortwave troughs could favor a more active weather
pattern.

HAZARDS

Moderate risk of much below-normal temperatures for southwestern Mainland
Alaska, Mon, Jan 5.

Slight risk of much below-normal temperatures across much of Interior Alaska,
southwestern Mainland Alaska, and the Alaska Peninsula, Mon-Wed, Jan 5-7.

Slight risk of high winds for the Alaska Peninsula, southern Mainland Alaska,
and southeastern Alaska, Mon-Wed, Jan 5-7.

Slight risk of heavy precipitation across the west coast of the CONUS, Mon-Thu,
Jan 5-8.

Slight risk of heavy precipitation across portions of the Lower Mississippi
Valley, Tennessee Valley, and Southeast, Tue-Sat, Jan 6-10.

Slight risk of heavy snow across portions of the Cascades, Klamath, and Sierra
Nevada Mountains, Mon-Thu, Jan 5-8.

Slight risk of heavy snow across portions of the Great Lakes and the Northeast,
Mon-Wed, Jan 5-7.

Slight risk of high winds across much of the CONUS west of the Rockies,
Mon-Thu, Jan 5-8.

DETAILED SUMMARY

FOR WEDNESDAY DECEMBER 31 - SUNDAY JANUARY 04:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR MONDAY JANUARY 05 - SUNDAY JANUARY 11: During week-2, the 0z ECMWF and
Canadian ensembles depict a quick mid-level pattern transition across the
Pacific with a weakening of the ridge to the south of the Aleutians, troughing
emerging across the central Pacific, and ridging near the west coast of the
CONUS by the end of week-2. This would be consistent with a weakening negative
phase of the Pacific North American (-PNA) pattern. The 0z GEFS is slower and
weaker with the pattern evolution, adding to some uncertainty with the eventual
outcome which could ultimately have implications downstream over the CONUS
later in week-2.



Troughing is predicted to build over western North America by the outset of
week-2 favoring enhanced precipitation chances along the West Coast. Both the
GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict at least a 20 percent
chance 3-day precipitation totals exceed the 85th climatological percentile and
1-inch across the entire West Coast early in week-2, with chances gradually
decreasing later in the period. Probabilities for reaching the 85th percentile
are initially higher (above 40 percent) in the ECMWF PET across the Southwest
compared to the GEFS PET, with uncalibrated tools favoring higher precipitation
totals over the Pacific Northwest. A broad slight risk for heavy precipitation
is posted across the entire West Coast, valid Jan 5-8, with a corresponding
slight risk of heavy snow across higher elevations of the Cascades, Klamath,
and Sierra Nevada Mountains supported by the GEFS snow water equivalent (SWE)
PET. Heavy snow is also possible further inland across the Great Basin and
Rockies, although probabilities for daily snowfall greater than 4 inches in the
ECMWF and GEFS ensembles are lower compared to probabilities farther
westprecluding inclusion in the hazard. While enhanced precipitation may
continue across the Northwest later in week-2 based on the ECMWF Integrated
Vapor Transport (IVT) tool, the potential for a more amplified ridge over the
West as depicted in the CMCE and to some degree the ECMWF ensemble would favor
less precipitation. As a result, the associated hazards are not extended later
into week-2 at this time.



Further downstream across the CONUS, multiple shortwave disturbances are likely
to propagate through the mean flow. Various deterministic solutions from the
ECMWF and GFS continue to indicate northern stream troughs moving through the
Northern Tier early in the period and some added potential of amplification
near the northeastern coast. This would be supportive of heavy snow or wintry
weather over the Great Lakes and Northeast, with the ECMWF ensemble mean
indicating at least a 20 percent chance of 3-day snowfall exceeding 4-inches
early in the period. While the 0z and 12z GEFS depict a weaker signal, the 6z
GEFS is more in line with the snowier ECMWF solution. While there is still
considerable uncertainty, a slight risk for heavy snow is highlighted across
portions of the Great Lakes and Northeast, Jan 5-7. Beyond this, the forecast
evolution is less certain. Both the ECMWF and GEFS PETs depict at least a 20
percent chance 3-day precipitation totals exceed the 85th climatological
percentile and 1-inch over parts of the Lower Mississippi Valley, Tennessee
Valley, and Southeast during the second half of the period associated with a
more active southern stream. This supports a slight risk for heavy
precipitation over these areas, Jan 6-10. The northward trajectory of this
moisture is uncertain, although a substantial high-latitude blocking ridge
predicted over northeastern North America could support greater amplification
of negative 500-hPa height anomalies underneath this feature later in week-2.
The 0z ECMWF ensemble is farthest east with this trough, generally favoring
drier conditions across the East compared to the GEFS and Canadian ensembles,
but also increasing the concern for colder temperatures.



Surface low pressure forecast over the Gulf of Alaska and relatively higher
pressures over Mainland Alaska favor a strong pressure gradient over southern
Alaska. This results in elevated chances for episodes of high winds across the
Alaska Peninsula eastward through Southeast Alaska. High winds would be
particularly favored in gaps and inlets. The PETs depict at least a 20 percent
chance wind speeds exceed the 85th climatological percentile and 40-mph over
some of these areas through the middle of the period. There is still some
signal for high winds at the end of week-2, but given increasing model spread
and a transitioning pattern there is insufficient confidence to issue a
full-week hazard. Therefore a slight risk of high winds is posted for most of
southern and southeastern Alaska for Jan 5-7.



PETs continue to highlight enhanced chances for temperatures to fall to near
hazardous thresholds across much of southwestern Mainland and Interior Alaska,
driven in part by the pressure gradient discussed above. A moderate risk of
much below-normal temperatures remains posted for southwestern Mainland Alaska,
Jan 5, where the largest negative anomalies (-20 deg F) are predicted before
decreasing in magnitude thereafter. Some interior areas may experience minimum
temperatures below -20 deg F, although areas closer to the southern coast are
becoming less likely to fall below 0 deg F. A broader slight risk is extended
across the Alaska Peninsula and Interior Mainland Alaska through Jan 7. 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 ECMWF ensemble favors quickly moderating temperatures, first
across eastern Mainland Alaska and progressing westward with time. While
slower, the 0z GEFS and Canadian also flip to a relatively warmer pattern by
the end of week-2.

FORECASTER: Thomas Collow

$$