Gale Warning 102, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
625 PM AKST Fri Jan 24 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tonight
through Monday)...

Key Points:

* Flood Advisories have been issued for many of the road and
  population corridors of Southcentral Alaska. A long duration
  rainfall, heavy at times, will fall on a frozen ground, limiting
  absorption of water into the ground. There is a high likelihood
  for widespread areas of ponding/standing water, especially for
  low lying or poor drainage areas and along smaller streams and
  creeks.

* Flood Watches remain in effect for the larger area outside where
  Flood Advisories are in effect. A new Flood Watch was added
  today for Kodiak Island and the southern side of the Alaska
  Peninsula. The areas at most risk for minor flooding are Chignik
  and the south end of Kodiak Island.

* The forecast for Storm Total Rainfall Amounts Friday morning
  through Monday Morning remains on track:

  -Western Kenai/Anchorage/Matanuska Valley/Kodiak Island: 1 to
   2.5"

  -Susitna Valley/Eastern Kenai/Prince William Sound: 2 to 6"

* A High Wind Warning is now in effect for Anchorage. The
  combination of wind and rain (and resulting standing water or
  wet ground) could bring down trees, particularly in areas where
  the ground is not frozen or where trees are already weakened
  from the recent windstorm. While wind strength will vary over
  the next couple days, with multiple ups and downs in speed,
  southeasterly wind gusts will reach around 70 mph on the
  Hillside and 30 to 50 mph for lower elevations of Anchorage and
  Eagle River.

* Winds will also be quite strong and gusty along the Knik River
  Valley into Palmer/Wasilla (peaking at 40 to 50 mph) and along
  the Copper River (peaking at 50 to 60 mph).

* Snow levels will rise Friday through Saturday, reaching as high
  as 3000 feet in the Mat-Su and 3000 to 6000 feet Saturday
  afternoon from Anchorage down to the western Kenai. The only
  areas along the road system that could remain mostly snow
  throughout this event are the north end of Broad Pass up to
  Cantwell; the top of Thompson Pass; and Paxson up to Isabel
  Pass. Winter Weather Advisories are in effect for all of these
  areas.

* Forecast confidence is now much higher for colder air moving
  across Southcentral Sunday night into Monday, changing any
  remaining precipitation to snow. The week ahead looks colder
  with potential for snow accumulation.

Satellite imagery this afternoon shows a highly amplified long-wave
trough/ridge pattern with the upper-level trough anchored over
eastern Russia and the ridge centered over the northeast Pacific.
Both features are anomalously strong for this time of year. The
result, a strong jet stream (150 kts+) and atmospheric river can
be found in between the low and ridge, northeastward to Interior
AK. A warm front extends northeastward from a low sitting south of
the eastern Aleutians. This front is lifting northward across the
Alaska Peninsula, western Gulf, and Kodiak Island. Precipitation
is overspreading Southcentral well out ahead of the warm front,
mainly in the form of rain at lower elevations where temperatures
are in the upper 30s to mid 40s. Gusty (pressure gradient driven)
southeasterly winds are also impacting much of Southcentral,
especially through the typical gaps (Turnagain Arm/Anchorage,
Knik River Valley/Palmer, and Copper River/Glennallen).

The forecast for the next couple days remains very much on track,
with only some fine-tuning of winds in the latest forecast. The
bottom line is that widespread minor flooding impacts are expected
and there could end up being more localized severe impacts. A lot
of water is going to fall on mostly frozen grounds. Since this is
highly unusual and likely record-setting rain event for the month
of January, it is a challenge to hone in on exactly how extensive
or extreme flooding will be.

There is now better model agreement on the evolution of the
pattern later in the weekend and into early next week, so did make
some more substantial changes to the forecast for Sunday
night/Monday. A short-wave trough will dig across the North
Pacific saturday night, develop into a closed low and track
northward up the west side of the ridge on Sunday - bringing the
surface low with it. As the low reaches interior Southwest AK,
cold air will wrap around the south side of the low and into
Southcentral Sunday night. A leading short-wave trough will
approach Southcentral during the day Sunday, helping to intensify
precipitation. The flow will back a bit toward the south to
southeast ahead of this trough, which looks like it will produce
downslope drying fro much of the western Kenai, Anchorage, and the
southern Mat-Su beginning midday Sunday. Thus, the heaviest
precipitation will be in the Prince William Sound region and the
west side of Cook Inlet up to the Susitna Valley. This trough will
help drive the ridge eastward Sunday through Sunday night.

The cold air will move in behind the trough with precipitation
becoming showery Sunday night through Monday. Strong gusty
southerly winds will spread inland and limit the ability of
surface temperatures to fall very far. Still, most of the region
can expect temperatures down around freezing by early Monday,
leading to some refreezing of standing water. The windy conditions
will likely cause temperatures to rise back above freezing during
the day Monday before dropping more significantly Monday night as
winds begin to diminish. The forecast beyond this point becomes
much more uncertain, with large model spread with storms tracking
into the Gulf. What can be said with some confidence is it will
be a return to more normal winter-time weather, with colder
temperatures and chances for snow.

-SEB/TM

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Days 1 through 3: Tonight through Monday)...

Key messages:

 - An extremely active pattern will continue to impact much of the
   outlook area this weekend into early next week, with impacts
   ranging from heavy snow and freezing spray to heavy rainfall.

 - The Winter Weather Advisory for the Kuskokwim Delta has been
   upgraded to a Blizzard Warning in effect through Sunday
   evening.

 - A Winter Storm Warning for heavy snowfall has been issued for
   the eastern Aleutians beginning later this evening.

 - A Flood Watch has been issued for the Chignik area due to
   potential for flooding from heavy rainfall through Sunday.

An extreme pattern that has not been observed in the historical
record for this time of year across southern Alaska is already
affecting much of the outlook area this afternoon. A significant
temperature and pressure gradient is now in place between an
Arctic air mass building over northeast Russia and a much warmer,
maritime air mass moving up from the Pacific into southern Alaska
around a very strong high pressure ridge centered south of the
Gulf. Near the gradient between these air masses, an atmospheric
river of moisture is now streaming up into the AKPen and much of
Southwest Alaska. This is helping to fuel moderate to heavy
rainfall from the eastern Aleutians out to much of Bristol Bay.
Farther north along the northern edge of this shield of
precipitation, temperatures are still cold enough for snow.
Moderate to heavy snowfall is ongoing across western portions of
the Lower Kuskokwim Valley out to much of the Kuskokwim Delta.

Much of the more impactful conditions over the weekend will
continue to be focused along the strong frontal zone between the
contrasting air masses outlined above. The biggest change in terms
of the progression of the pattern through the weekend involves the
low now beginning to develop south of the Aleutians. This low
looks likely to become much stronger compared to some earlier
indications as it lifts north into Bristol Bay through Sunday.
This change has been reflected in this forecast package, including
much stronger winds for much of the Bering and Aleutians on the
west side of the low as it lifts north. Snowfall rates also look
like they will be even more impressive along the main band
setting up along and north of the front and to the west of the low
center as it heads north. Up to 2 feet of snowfall is now
anticipated for parts of the Kuskokwim Delta, where a Blizzard
Warning is now in effect. True blizzard conditions will likely
hold off until Saturday night as north winds increase ahead of the
approaching low, then continue into Sunday. Meanwhile, rain will
transition to snow across the eastern Aleutians late tonight into
Saturday morning. Here, heavy snowfall will persist until the low
begins to pull to the north and into Southwest late on Sunday.

On the warmer side of this system, heavy rainfall is expected to
persist for about the next 36 to 48 hours along mainly south-
facing slopes along the AKPen and across much of Bristol Bay. The
main area for possible flooding concerns due to the prolonged
moderate to heavy rainfall will be focused near Chignik, where a
Flood Watch is now in effect.

The story from Sunday into Monday will quickly transition into
what continues to look like a sudden, significant cold snap. As
the low heads up into the Interior on Sunday, the Arctic air mass
currently sitting up near Siberia will surge southeast and rapidly
drop temperatures from the 30s and 40s down into the -0s to 10s
across much of Southwest between Sunday and Monday. Temperatures
will not drop as dramatically across the Aleutians, but are still
expected to dip below freezing along much of the Chain. Steady
snow will also give way to scattered snow showers across both the
Aleutians and Southwest on Monday as the threat for steadier,
heavy rain/snow comes to an end. Heavy to extreme freezing spray
rates will also develop over water as the cold air mass surges
south from Sunday into Monday, mainly across the northern Bering
Sea near Nunivak Island, Saint Matthew Island, and parts of the
Southwest Coast. Stay tuned as we continue to follow this very
active pattern throughout the weekend.

-AS

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

Key takeaways:

	- Deep southerly winds and heavy precipitation shifts away from
   the southern coast towards the Panhandle.

	- Significant pattern shift spreads colder temperatures across
   the forecast area early in the work week.

On the upper level Alaska Weather map, a long wave trough
continues with an Easterly track over Mainland Alaska by the end
of the forecast period. A number of shortwaves provide the energy
for changes. The ECMWF anchors the strengths and trajectories
through the week, as the GFS becoming more of an outlier. The
UKMET and Canadian models clusters closely with the ECMWF by
Thursday. The strong warm air intrusion across the Southcentral
diverts Eastward with the changing pattern. Coming in from the
Northwest, colder air begins to sweep into Western and Interior
Southcentral Alaska through Thursday.

On the surface, a well developed low and front muscles across the
Interior, pushing the heavier rainfall and gusty winds over
Prince William Sound into the Southeast Panhandle through midweek.
Locally heavy snow moves in from the Southwest and West and along
the Alaska Range across the Canadian Border by Thursday. Out
West, gusty winds and broad areas of snow move from the Central
Aleutians and Bering over the Alaska Peninsula through Tuesday. A
developing low over Kamchatka brings another round of snow and
gusty winds across the Southern Bering and Aleutians into the
North Pacific by Wednesday.

&&

.AVIATION...

PANC...A prolonged event of rain and gusty winds will allow for
periods of decreased visibilities through Sunday. Visibilities may
bounce primarily between VFR down to IFR as rain intensity
increases and decreases. Gusty southerly to southeasterly winds
are expected with gusts up to 45 kts through Sunday evening.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
109 AM AKST Sat Jan 25 2025

AKZ112-260200-
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
109 AM AKST Sat Jan 25 2025

...STRONG WINDS FOR PARTS OF THE MATANUSKA VALLEY THROUGH SUNDAY
AFTERNOON...

Strong east to southeasterly winds will continue across the
the Matanuska Valley through Sunday afternoon as a potent storm
system moves through the region. Winds 20 to 35 mph with gusts to
60 mph are possible for the Knik River Valley and Palmer. For
areas west of the Parks and Glenn Highway Interchange, including
Wasilla, winds 15 to 25 mph with gusts to 40 mph are possible.

There will likely be multiple peaks and lulls in the overall
strength of the winds through Sunday, but they will largely
remain gusty the entire time.