Gale Warning 47, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 AM AKST Sat Jan 11 2025

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

Key Points:

* Winds with first of two storms have peaked for most of
  Southcentral and will diminish through the day.

* The second stronger storm is largely on track for tonight
  through Sunday night, bringing widespread strong winds and
  precipitation to Southcentral.

* High Wind Watches are in effect for late tonight through Sunday
  afternoon for Anchorage, the Matanuska Valley, Portage Valley
  and East Turnagain Arm, and Cordova. There is increasing
  confidence that this could produce damaging winds, especially
  for portions of the Anchorage area.

* Coastal areas will see periods of heavy rain at lower elevations
  and heavy snow in the mountains. With multiple inches of rain
  likely, this could lead to flooding along areas streams,
  especially across the eastern Kenai Peninsula where a Flood
  Watch is in effect.

* Inland areas will see much less precipitation, though most areas
  will still see periods of precipitation accompany the winds.

* Much colder air will move in aloft Sunday night into Monday,
  causing any remaining precipitation to change to snow. All
  signs point to a shift in the overall pattern, with a return to
  more seasonable temperatures and chances of snow for
  Southcentral Alaska next week.

A deep low is centered southeast of Kodiak Island early this
morning, with a leading occluded front pushing onshore of
Southcentral. Winds have peaked ahead of the front for most areas
and started to diminish. This trend will continue through the
day. The bulk of precipitation is falling in coastal areas, with
low elevation rain and high elevation snow. Snow is falling along
higher elevations of the Seward Highway (Turnagain Pass, Summit
Lake) as well as through Thompson Pass. There is now good model
agreement in a low track to western Prince William Sound this
afternoon. This will send the area of highest pressure rises
behind the low toward eastern Prince William Sound and the Copper
Basin late today, leading to gusty southerly winds.

Attention will then quickly shift to the second larger and
stronger storm. Recent model runs remain consistent with the
synoptic solution, with just minor fluctuations in the track of
key features. Thus, the overall forecast is on track and
confidence in the greatest impacts of wind and heavy precipitation
is increasing. One of the biggest threats is for a damaging wind
storm in the Anchorage area late tonight through early Sunday
morning. Forecast soundings show a definitive critical layer,
with a wind shift from southeast to south or south-southwest
above mountain top. This can be conducive to formation of mountain
waves and rotors. Model soundings vary more on the atmospheric
stability. The occluded front crossing the western Gulf should
bring some warm air northward, but not a lot. Additional warming
will occur as air sinks off the mountains, though this could also
be limited by a moist atmosphere. In any case, these phenomena,
which can lead to very strong and erratic winds, are notoriously
difficult to forecast because they are very sensitive to the
atmospheric conditions for which we have limited ways to monitor
when dealing with conditions above the surface. For now, have
decided to stick with a High Wind Watch for Anchorage. However,
there are some other key factors which have led to a slight
adjustment to the area at risk of high winds. At the time the
potential for mountain waves looks greatest, the low will be
positioned over the southeastern Bering Sea, with the occluded
front over the western Gulf. With much lower pressure at the south
end of Cook Inlet, this will lead to a strong down-inlet pressure
gradients which will keep the Turnagain Arm jet south of
Anchorage. This gradient combined with a lee side trough just west
of the mountains (due to the downslope flow) looks like it will
induce a fairly robust west to northwest wind at the surface for
areas along Knik Arm and down into north to west Anchorage. With
nothing to drive the winds inland at this point, the threat of
high winds will be highest along and right near the Chugach
Mountains, including East Anchorage and Eagle River. By the time
the surface low gets far enough north to induce the Turnagain Arm
jet to bend northward, winds will already have started to weaken.
Thus, the threat of high winds for north to west Anchorage (and
areas further from the mountains looks minimal). Confidence in
reaching at least 75 mph or greater along the Upper Hillside is
high. Will wait on one more model cycle to finalize decisions on
Wind Watches, but if there are no big shifts in key features,
these will likely be upgraded to High Wind Warnings.

No other substantive changes have been made to the forecast. Stay
tuned to your local forecast for details on what will surely
impact travel across the region and could lead to damage and/or
power outages in some locations. The impacts from this storm will
last all the way into Monday, with gusty southerly winds and snow
showers lingering, but with improving conditions through the day.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Monday night)...

A storm-force low centered southeast of Kodiak Island extends a
front across the Alaska Peninsula, the eastern Bering Sea, and
into the Kuskokwim Delta this morning. This frontal position is
further west than previously forecast, which has allowed most of
Bristol Bay, including Dillingham and communities to the west to
see precipitation end and temperatures warm into the mid to upper
30s. Meanwhile, temperatures remain closer to freezing in the
Kuskokwim Delta with light snow falling. Up to an inch of snow is
forecast as the low lifts into Southcentral today. The front,
though it weakens, will push back into Bristol Bay around midday
with colder air working back into Southwest Alaska. This will lead
to a brief round of snow or rain for most coastal locations,
though precipitation changes to showers and diminishes as it
pushes further inland this afternoon and evening.

A second, stronger and larger low pressure system enters the
eastern Bering Sea from Saturday into Saturday night. Strong
southeast winds will spread into Southwest Alaska through
Kamishak Gap into the greater Bristol Bay region along with rain
and snow moving back across much of the area as well. Northerly
gale force winds set up across the Pribilof Islands and eastern
Aleutians, bringing in a colder air mass from the western Bering
Sea. Much of the model guidance continues to situate the western
periphery of a front right along the Pribilof Islands, which leads
to significant uncertainty in the potential for low visibility
and blowing snow. Since yesterday, the model consensus has
shifted ever so slightly eastward, decreasing the likelihood of
significant visibility reductions somewhat. Regardless, a slight
westward shift in track, which remains possible at this time,
would lead to blowing snow with one mile visibility or less, while
an eastward shift would eliminate the potential entirely. Further
north, 4 to 8 inches of snow accumulation is expected for Nunivak
Island and the Kuskokwim Delta coast from Kipnuk north Saturday
night into early Sunday morning, for which a Winter Weather
Advisory is now in effect. Confidence is low at this time, but
blowing snow is possible for portions of Southwest Alaska as the
low lifts northward, bringing a push of southwesterly winds along
with snow showers. However, any significant visibility reductions
would likely be isolated to a small area for a short time.

Out west, a compact gale or storm force low looks to track near
the western Aleutians. With a cold air mass moving into the
western Bering Sea, there is also potential for blowing snow for
those islands Sunday evening. The cold air mass spreads across the
Bering Sea and into Southwest Alaska with the northward exit of
the large low Sunday night, dropping temperatures into the 20s for
Monday and into the teens Monday night. Expect a general drying
trend across the region as well for the beginning of next week.

Quesada/Eovino

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

On the Alaska Weather map, an elongated upper level trough
stretching from the Russian Far East across the Aleutians and
Bering. This trough gets a little boost from passing shortwaves to
reorient over Southwest Alaska and the Gulf of Alaska for
midweek, before continuing its Eastward track into Canada by
Thursday. An upper ridge building across the Western Aleutians
Tuesday moves to extend across the Gulf of Alaska and Western
Alaska into Northeast Russia through the end of the week.
Deterministic GFS and ECMWF carry the features and changes well
through Thursday with the Canadian models joining up into the
weekend.

A decaying surface low on the Southcentral coast spreads locally
heavy rains along the coastal locations, with locally heavy snow
further inland and over higher elevations through Wednesday. A
second low over the Shumagin Islands brings mostly rain with snow
over Bristol Bay from the Eastern Aleutians, Alaskan Peninsula and
Kodiak Island through midweek, before moving over the Kenai
Peninsula before dissipating over Prince William Sound Thursday.
Bands of snow progress across the Bering through Thursday. A well
developed North Pacific low and fronts spreads snow changing to
rain across the Western and Central Aleutians Wednesday and
continues over The Bering, Southwest Alaska and the AKPEN by
Friday. Gusty winds with gale force gusts work their way from the
Central Aleutians over the AKPEN and Bering through Friday.

&&

.AVIATION...

PANC...VFR conditions will largely prevail for most or all of the
TAF period thanks to persistent strong southeasterly flow across
the mountains. The much more challenging part of the forecast will
be winds, with multiple shifts in direction and speed expected as
features move through the area. A surface front will pass through
early this morning, which typically leads to southeast Turnagain
winds bending into the terminal. However, with a deep low down
over the Gulf, pressure gradients favor keeping the Turnagain jet
south of the terminal until about midday as the low moves into
the northern Gulf and pressure gradients in Cook Inlet weaken.
Until then, low level wind shear will remain a likelihood with a
surface wind out of the west to northwest and southeast flow
aloft.

Southeast winds will then strengthen as a new storm system tracks
out of the North Pacific toward southern AK this evening. As the
leading frontal boundary crosses the Gulf, it will again cause
winds to bend down Cook Inlet toward lower pressure, leading to
another wind shift back to west to northwest and redevelopment of
low level wind shear. Tonight's system will be much stronger than
the current storm with a much stronger Turnagain Arm Jet. In
addition, conditions look favorable for mountain waves to form
along the Front Range Chugach, leading to strong erratic winds.
While these likely won't reach the terminal, it does look like a
good set-up for extremely strong low level wind shear. At some
point tomorrow morning, strong and gusty southeasterly Turnagain
winds will then bend into the terminal. There is uncertainty in
timing and strength, as the Turnagain jet will begin to weaken
before bending northward into Anchorage.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
324 PM AKST Sat Jan 11 2025

AKZ195-120700-
Pribilof Islands-
Including the city of Saint Paul
324 PM AKST Sat Jan 11 2025

...SNOW AND BLOWING SNOW TONIGHT THROUGH SUNDAY MORNING...

A strong low tracking into the eastern Bering Sea tonight will
bring north to northwesterly winds gusting as high as 50 mph for
the Pribilof Islands. Confidence has increased that the islands
will be impacted by snow on the western edge of precipitation
associated with the low. Snow showers, combined with gusty winds,
are expected to reduce visibilities to below one mile at times,
with potential for visibilities dropping as low as one-half mile.
Travel may become hazardous tonight through Sunday morning. Use
caution if traveling during this time.