Gale Warning 174, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKST Sun Feb 11 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Wednesday)...

A weakening gale force low is centered near the Barren Islands
this afternoon, pushing a front into the southern Kenai Peninsula
and across the northern Gulf of Alaska. Surface temperatures in
the low to mid 30s along the coast are leading to precipitation
falling mostly as snow. The low will continue to press northward
into Prince William Sound through the next hour or two, bringing
a round of steady snowfall that will bring 3 to 6 inches of snow
to the Valdez and Cordova areas through early Monday morning. For
inland areas, precipitation chances have been increased a little,
with numerous showers possible along the western Kenai Peninsula
this evening, and scattered showers for Anchorage and the
Matanuska Valley closer to midnight as the greatest forcing and
instability associated with the front lifts northward.
Snow accumulations with these showers are expected to be minimal -
less than an inch. Upsloping along the Talkeetna Mountains and in
the northern Susitna Valley may lead to more numerous snow shower
development later tonight.

Focus then shifts to a low tracking from the North Pacific toward
the Alaska Peninsula, helping to amplify the upper-level pattern
and build strong ridging over the eastern Gulf and nudging into
Southcentral Alaska. The low will lift a warm front across the
coastal mountains around mid-day on Monday as pressure falls out
west, leading to a rapid increase in southeasterly winds across
the area, with the typical enhanced winds through mountain gaps.
Additionally however will be the threat of high winds,
particularly for the Anchorage Hillside, as much of the model
guidance is hinting at an inversion setting up between 850 and 700
mb allowing a layer of 65 knot (75 mph) wind gusts to mix down to
between 2000 and 4000 ft above sea level. A High Wind Watch has
been issued to highlight this potential. Modestly unstable air in
the lower levels may also allow wind gusts up to 40 mph or higher
at times in portions of the Anchorage Bowl, but there is currently
high uncertainty in the timing and strength of the winds. With the
arrival of southeasterly winds in the afternoon, expect
temperatures to rise back into the upper 30s, likely hitting 40 in
spots. Temperatures will hover in this range as long as the winds
stick around, which currently looks to last through at least
Tuesday, with potential successive rounds of (likely weaker)
southeasterly winds into Wednesday.

Further west, a negatively tilted trough will extend from the
Bering Sea southeastward into the northeast Pacific, directing an
upper level jet and atmospheric river at the Alaska Peninsula and
continuing up across western Alaska. Model spread is less than in
previous days, though there are still some minor differences in
surface low track as well as exact placement of the jet and
atmospheric river. Based on the mean position, it looks highly
favorable for Kodiak Island to see a prolonged period of rain
beginning Monday. The area of steady precipitation will extend up
to the Alaska Peninsula and the west side of the Cook Inlet and
possibly as far north as the western Susitna Valley. The
strengthening winds will also lead to some upslope precipitation
along the coast. If the atmospheric river remains pointed at the
same location for multiple days, there will be some potential for
flooding. While confidence in the details is not great, Kodiak
Island (particularly the southern half) will be one place to
watch for heavy prolonged rainfall and the flooding potential.

CQ

&&

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

A short break in the weather this afternoon as the system which
brought wind, rain and snow to Southwest Alaska has moved north
over the Seward Peninsula. In it's wake, expect diminishing winds
and isolated snow showers mostly over the Kuskokwim River delta.
Over the Bering, more of the same is expected. Light (by Bering
standards) westerly to northwesterly winds and snow showers will
persist as weak features move overhead and cold air producing
steep lapse rates continues to move south out of the Gulf of
Anadyr.

A strong Pacific storm is expected to cross the Alaska Peninsula
Monday morning. This will bring strong southeasterly winds and a
mix of rain and snow. For Monday, Kipnuk and Toksook Bay could
see a couple inches of snow. Togiak and Dillingham could see
several inches of snow through Tuesday. For now, the most likely
areas for rain are interior Bristol Bay and the Lower Kuskokwim
Valley. Strong winds will increase temperatures above freezing for
much of the Mainland, so high temperatures above freezing can be
expected over the next 1-2 days. Moisture associated with this
system looks to be fairly high due to the high amplitude pattern
and southerly jet stream. For the most part the Alaska Peninsula
will be spared from heavy rain due to downsloping off of the
Aleutian Range, but Chignik could receive multiple inches of rain.
For now, the bulk of the moisture will pass between Port Heiden,
and Pilot Point over the western southwestern coast.

&&

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

The long term begins with a stagnant upper-level ridge / trough
pattern east to west across the state. A 560dm ridge anchored over
the St. Elias Mountains Wednesday drifts northeast over the Yukon
for Friday before weakening and elongating as it continues a slow
push to the southeast over British Columbia. The broad trough over
the Bering and Aleutians also remains in place through the end of
the week. The result is a general west to southwesterly flow in
the mid levels across the southern Bering and Aleutians shifting
to a southerly flow from the western Gulf and Alaska Peninsula
north along the west coast of Alaska. Various shortwaves embedded
in the flow, along with a strong upper-level jet, are resulting in
a seemingly continuous parade of surface lows and troughs moving
from the North Pacific toward the Alaska Peninsula and Kodiak,
eventually moving farther north to the Bering Strait.

This storm track favors periods of heavy precipitation, in the
form of low elevation rain and mountain snow, from Kodiak Island
to the Alaska Peninsula and along the south-facing hills and
mountains of Southwest Alaska, due to upsloping. With multiple
surface lows tracking north across the Alaska Peninsula, strong
southeasterly gap winds and mountaintop winds are also likely,
with the strongest of the gap winds across the Alaska Peninsula
and through Kamishak Gap into the interior Bristol Bay region.
The southeasterly flow will also promote periods of showers
across the Kenai Mountains along with strong southeasterly gap
winds, mainly through Turnagain Arm and across the Matanuska
Valley.

The greatest uncertainty comes closer to the weekend, as models
try to weaken the ridge at differing times with the weaker, more
easterly positioned ridge and upstream trough becoming more
negatively tilted. This scenario would likely allow for storm
systems to move farther north into the Gulf of Alaska with
steadier precipitation moving toward the Southcentral coast.

-TM

&&

.AVIATION...

PANC...General VFR conditions and light winds persist through
Monday. There is the potential for a brief period of MVFR ceilings
and visibility due to snow shower activity late this evening into
early Monday morning as trough lifts north over Anchorage. LLWS is
expected to develop by late Monday morning as southeasterly winds
quickly increase across Turnagain Arm and the Anchorage Hillside
while light northerly surface winds remain over the terminal.

-TM

&&