Gale Warning 108, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
602 PM AKST Sat Jan 25 2025

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

Key Points:

* Flood Advisories continue 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 including Chignik and the south
  end of Kodiak Island.

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

  -Western Kenai/Anchorage Area/Matanuska Valley/Kodiak Island:
   1 to 2.5" - lower in western and northern Anchorage

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

* A High Wind Warning continues 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 55 mph) and along
  the Copper River (peaking at 50 to 60 mph).

* Winter Weather Advisories remain in effect for Turnagain pass to
  Summit Lake as well as Thompson Pass.

* 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 much
  colder with potential for snow accumulation.

The mean longwave trough slowly advances eastward as it lay draped
across the Bering and Western Aleutians. A north Pacific High
remains parked off of the coast of Washington allowing a deeply
tapped tropical moisture plume from Hawaii to take aim at Alaska.
A surface low south of Cold Bay has an occluded front which
continues to be the boundary between the warm and moisture rich
air flowing into southcentral and the colder air out to the west.

While the ongoing forecast hasn't changed and remains on track,
some small nuances can explain why rain seems to be under-performing
for parts of Anchorage and over-performing for others. Strong
winds in Turnagain Arm are significantly warming and drying the
atmosphere on the lee (western) side of the Chugach. The event,
currently, is being forced by orographic lift despite record
precipitable water. Sources of dynamic lifting (shortwaves) are
limited. They are noticed as they rotate across the area as the
'dry' areas of west and north anchorage see periods of relatively
heavy rain. Rainfall totals as the early afternoon range widely
from PANC to the Hillside. Western Kenai has seen more than the
road from Sterling through the Chugach. As the evening wears on,
winds should start to weaken some and rain should be a bit more
uniform from the city through the Hillside overnight.

-- previous discussion --

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 for 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/SS

&&

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

Key messages:

 - A very active pattern will continue to affect much of the
   outlook area with impacts ranging from heavy snow, heavy
   rainfall, blowing snow, rapidly falling temperatures and heavy
   freezing spray through early next week.

 - Multiple winter headlines remain in effect for the eastern
   Aleutians, Lower Kuskokwim Valley, and the Kuskokwim Delta.

 - Winter Weather Advisories have been issued for the southern
   coastline of Bristol Bay down to the southern end of the AKPen
   from Sunday evening to Monday evening due to potential for
   strong winds, snow and blowing snow.

A historic pattern that has not been observed in modern records
across parts of Alaska during the latter half of January continues
to impact much of the outlook area this afternoon. A very strong
frontal zone still separates an Arctic air mass building over the
northwestern Bering and a much warmer air mass moving up from the
Pacific Ocean. An atmospheric river continues to ride up along a
zone of very strong southwesterly flow into the Alaska Peninsula
and across Southwest, where some of the more inclement conditions
are occurring. Near whiteout conditions in heavy snowfall have
persisted much of the day across the Kuskokwim Delta, and
conditions here will deteriorate further overnight as winds pick
up and begin to cause blizzard conditions to develop. Similar
conditions are occurring across the eastern Aleutians, where
strong and gusty north winds are combining with heavy, wet snow to
cause very poor visibility. Snow is worsening in intensity as a
deformation band develops northwest of a low beginning to move up
along the front from the North Pacific.

The forecast thinking overall for the next day or two remains
largely unchanged, with the overall progression of the low still
looking on par with expectations. The low will steadily deepen as
it crosses into the Bering Sea on Sunday, then move into
Southwest on Monday. Two new Winter Weather Advisories have been
added to the list for the southern coastline of Bristol Bay as
well as the northern coastline of the Alaska Peninsula, but these
are not set to go into effect until later on Sunday. As the low
begins to move up into Southwest, it will pull much colder air
spreading across the Bering Sea up into Bristol Bay between Sunday
and Monday. Temperatures will very quickly fall from the 40s to
10s to 20s as rain also changes over to snow, leading to a
potential flash freeze. Snow and blowing snow is expected mainly
along the coast from King Salmon down to Cold Bay as gusty west
winds quickly develop Sunday afternoon and persist into Monday.

Between Monday and Tuesday, conditions should improve across the
board as the low heads up into the Interior and leaves behind a
cold pattern along with scattered snow showers across much of the
region. Heavy to extreme freezing spray rates already developing
along and just south of the ice edge and near the Kuskokwim Delta
Coast should also improve as gusty north winds slowly begin to
subside.

-AS

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday - Saturday)...

A series of lows move through the northern Gulf of Alaska mid-
week through the end of this week causing coastal rain and
mountain snow to Prince William Sound inland to Copper River
Basin. Cooler air will filter from the Interior to the Kenai
Peninsula, Kodiak Island, Anchorage and Mat-Su Valleys bringing
the return of more seasonable late January temperatures.
Precipitation during this time is favoring a rain/snow mix later
this week with the chance for snow for the weekend.

Northwest winds bring cooler air into the Southwest and AK Pen
through the end of this week as a trough moves across the Bering.
Winds on the Pacific side of the Eastern Aleutians and AK Pen
could be strong mid-week. Locations in the Southwest turn warm
this weekend as a front moves across the region reaching the
Southwest by the weekend. This will push cooler end-of-week air
eastward.

-DJ

&&

.HYDROLOGY...

*** Flood Advisories and Flood Watches in Southcentral remain in
 effect into Sunday evening. ***

A deep and persistent plume of moisture will continue to flow
northward from the Pacific Ocean into Southcentral this weekend.
This moisture plume, referred to as an Atmospheric River,
will continue to bring copious amounts of rainfall in multiple
waves to Southcentral through tomorrow evening. Rainfall across
most of the region falling onto frozen ground is resulting in
ponding on roadways slow drainage/low lying areas and
rising/overflowing of creeks and streams.   QPF amounts the next
24-36 hours range from 1.5" to 5" across Southcentral with the
highest amounts along the Eastern Kenai Peninsula and Kodiak
Island. The final wave of moisture moves through Sunday evening.
The three day rainfall event from January 18-21, 1961 of 1.34" is
the most rain over three days in a meteorological winter (Dec-
Feb) in Anchorage. Only a trace of snow fell during these three
days combined.

-DJ

&&

.AVIATION...

PANC...A prolonged event of rain and gusty winds will allow for
periods of decreased visibilities through Sunday. Visibilities may
vary between VFR down to IFR with rain intensity. Southerly to
southeasterly winds are expected with gusts up to 45 kts through
Sunday evening. Rain will begin to wind down Sunday afternoon
through evening with winds gradually decreasing but remaining
south-southeasterly.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
235 AM AKST Sun Jan 26 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0205 AM     Snow             8 SW Trapper Creek      62.32N 150.23W
01/26/2025  M10.9 Inch       Matanuska-Susitna  AK   Trained Spotter

            UPDATE: 5.6 additional inches of snowfall
            since 7PM 1/25/25. Total snowfall in the
            past 12 hours is 10.9 inches. Total
            precipitation in the past 18 hours is 2.23
            inches. SWE for the past 6 hours is 0.79
            inches with a snow of about 7.1 to 1. Temp
            nearly constant at 30.9 degrees.

&&

DAN