Storm Warning 34, NWS Anchorage, AK

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

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

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 55 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.

* Snow levels for the eastern Kenai dropped below 1000 ft
  overnight with snow accumulation from the Whittier Tunnel and
  Turnagain Pass to Summit Lake. While snow levels are expected to
  rise today, snow levels will likely drop back below 1000 ft for
  these locations with additional snowfall late Saturday night
  through Sunday morning.

* 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 longwave pattern remains much the same this morning, with a
trough extending from the Bering Strait south to the Western
Aleutians and a ridge parked over the northeastern Pacific. A
strong subtropical jet is streaming over the central Pacific,
taking a left turn north of Hawaii and streaming north across the
Alaska Peninsula. Multiple shortwaves are riding north along the
jet, taping into copious moisture from the tropical Pacific. This
has resulted in an atmospheric river pointed at the state of
Alaska.

A stationary front extends from an occluded low south of the
Eastern Aleutians northeast over the Yukon Flats. This is
providing the boundary between warmer air streaming into
Southcentral Alaska and colder air to the west. several upper-
level shortwaves moving with the jet is also helping to aid in the
enhancement of precipitation and strong southeasterly gap winds.

The forecast for through the next 24 to 48 hours remains very
much on track. Any breaks in the precipitation this morning will
likely fill in quickly as the next shortwave rounds the ridge and
drives a surface trough to the coast. 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. In addition to the expected rainfall, it also
looks like snow levels will drop slight again late tonight into
early Sunday, similar to what was observed overnight yesterday
into early Saturday morning. Locations from Portage to Turnagain
Pass and Summit Lake saw a transition to snow with several inches
of accumulation. Snow levels should rise above the road network
again today, but will be back below 1,000 ft tonight, with
another round of snow for these same locations.

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 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

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Days 1 through 3: Today 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, freezing spray, heavy rainfall, and
   significant drops in temperatures.

 - A Blizzard Warning for the Kuskokwim Delta remains in effect
   through Sunday evening.

 - A Winter Storm Warning for heavy snowfall over the eastern
   Aleutians remains in effect through Sunday afternoon.

 - A Winter Weather Advisory for snow over the Lower Kuskokwim
   Valley remains in effect through Sunday afternoon.

 - A Flood Watch over the Chignik area due to potential for
   flooding from heavy rainfall remains in effect through Monday
   morning.

A historically unusual pattern not experienced during this time of
year over southern Alaska is continuing to affect much of the
outlook area this morning. 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. Moderate
to heavy snowfall is already ongoing over the Kuskokwim Delta and
western portions of the Lower Kuskokwim Valley, while Unalaska
has recently started to transition over to snow as temperatures
continue to fall. Over Bristol Bay, temperatures at lower
elevations remain above freezing, resulting in mostly rain taking
place over the area.

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
developing low south of the Aleutians. Similar to Friday
afternoon's discussion and forecast package, model guidance is
picking up on a more robust low that will lift to the northeast
towards Southwest through Sunday. Winds and gusts over much of
the Bering and Aleutians were further increased in this forecast
package, especially on the west side of the low where strong cold
air advection is trying to fill in. Snowfall rates continue to be
impressive with the main frontal band of this system as it shifts
north, especially to the north and west of the low center. An
additional 2 feet of snow is anticipated for portions of the
Kuskokwim Delta through Sunday afternoon, while intense blizzard
conditions closer to the coastline will take place starting
Saturday night as stronger northerly winds begin to increase.

On the warmer side of this system, heavy rainfall is expected to
persist for about the next 24 to 36 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 remains in effect through Monday morning.

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.

-BS/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
will vary with rain intensity between VFR and IFR. Southerly to
southeasterly winds are expected with gusts up to 35 kts through
Sunday evening.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1104 AM AKST Sat Jan 25 2025

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

0734 AM     Rain             8 S Talkeetna           62.23N 150.07W
01/25/2025  M1.49 Inch       Matanuska-Susitna  AK   Public

0913 AM     Snow             5 E Valdez              61.11N 146.22W
01/25/2025  M4.6 Inch        Chugach            AK   Public

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1250 PM AKST Sat Jan 25 2025

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

1100 AM     Rain             7 NW Palmer             61.69N 149.21W
01/25/2025  M0.60 Inch       Matanuska-Susitna  AK   Public

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
129 PM AKST Sat Jan 25 2025

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

0127 PM     Flood            Anchor Point            59.77N 151.84W
01/25/2025                   Kenai Peninsula    AK   Public

            Public reported flooding along the Anchor
            River near the Old Sterling Highway and
            along the Sterling Highway near mile marker
            161.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
146 PM AKST Sat Jan 25 2025

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

0120 PM     Rain             Amber Lake              62.17N 150.54W
01/25/2025  M1.90 Inch       Matanuska-Susitna  AK   CO-OP Observer

            Rained all night through 1 pm then turned
            over to heavy snow just after 1 pm.

&&

PP