Gale Warning 140, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKST Sat Feb 11 2023

.ANALYSIS AND UPPER LEVELS...

An upper level longwave trough dominates most of Alaska and the
Bering Sea, anchored by a broad upper level low over St. Matthew
Island. A shortwave trough extends over much of Southern Alaska
and the Gulf. At the surface, a decaying surface low lingers over
Bristol Bay and Kodiak Island. With this low weakening, the
weather has been active, but relatively benign, over the forecast
area. For the Bering Sea, Pribilof Islands, and Aleutian Chain,
northerly flow is ushering in snow showers and gusty winds. Over
the Southern Mainland, the Bethel, King Salmon, and Kenai radars
show light snow spreading across large portions of both Southwest
and Southcentral Alaska. For the Gulf of Alaska, Middleton Island
radar shows rain as the primary precipitation type. With
temperatures warming up above freezing in Prince William Sound,
there have been a few observations of snow mixed with rain.

The jet stream remains amplified south of Alaska, with a
northward curve toward the Gulf. This will set the stage for a
North Pacific shortwave and its attendant surface low to transit
towards the north Gulf coast later this weekend.

&&

.MODEL DISCUSSION...

Models remain in decent synoptic agreement. The biggest challenge
in the near-term will involve a low tracking into the northern
Gulf tonight. Models seem to be slowly converging in the middle
as compared to yesterday's distinctly different solutions between
the GFS/EC and NAM/Canadian. Overall impacts due to model
differences mostly involve finer details with marine winds and the
timing of precipitation through interior Southcentral. Further out,
models remain in decent agreement regarding the general track and
strength of a low pushing into the Aleutians on Monday.

&&

.AVIATION...
PANC...VFR conditions in the morning may drop to MVFR at times as
periods of light snow reduce visibility. Prevailing MVFR
conditions are expected by noon as ceilings lower in advance of
light snow this afternoon and evening, with the potential for IFR
visibilities during periods of heavier snow. Confidence in
snow timing and intensity remains low to moderate given the weak
shortwaves moving across Southcentral.

&&

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

An active weather pattern continues across Southcentral Alaska for
the next few days as a series of lows move through the area.
Widespread gale and storm force winds along the coastal waters of
the northern Gulf will ease this evening and tonight. Strong
downslope forcing will remain in place across the Anchorage Bowl
and thus result in minimal precipitation with this first system.
The next low will then move in Saturday night into Sunday morning.
Downslope forcing is expected to be weaker with this next low
which means the chance for snow will be greater in Anchorage than
compared to this first low. Strong cold air advection is expected
in the wake of this second low on Monday. This strong cold air
advection will result in widespread storm force winds with
hurricane force gusts likely in the bays and passes. Heavy
freezing spray is also likely across the western Gulf on Monday as
a result of the strong winds combined with cold temperatures.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Monday)...

Broad upper level longwave troughing extends across Southwest
Alaska, with a series of shortwaves wrapping around the trough.
Lingering snow showers will persist through the rest of the weekend,
but very little additional snow accumulations are expected. Cold
air advection is on a pretty linear west to east track that will
encompass Southwest, with frigid overnight temperatures reaching
into the minus 20's by Sunday night and a gradual decline into the
sub-zero range during the day by Monday.

&&

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

The majority of the Bering Sea will continue to see improving
conditions. Cold air advection is moving west to east, enhancing
winds south of the Alaska Peninsula Sunday night, most notably out
of bays and passes. Areas of storm force gusts and heavy freezing
spray are expected from Wide Bay to Chignik Bay Sunday and Sunday
night. Additionally, areas of extreme freezing spray will continue
along the ice edge through Sunday, with heavy freezing spray
reaching south to the Pribilof Islands and along the northern edge
of the southern Alaska Peninsula. The next system approaches the
Aleutian Chain Monday morning. The storm force front pushes
northeastward over the Central Aleutians Sunday afternoon. The
strongest winds will likely remain over the Central Aleutians as
they wrap around the backside of the low, but there is a chance
for them to push towards the Pribilof Islands. There remains some
inconsistency with this system regarding low track and timing of
winds/precipitation. There will be a transient push of some warmer
air, but there is poor agreement on when that comes in. The
current trend is that colder air will hang on along the leading
edge of the front, with the initial band of precipitation
remaining as snow along the Central Aleutians that, when coupled
with the increased winds, could lead to periods of blowing snow
Sunday night, before transitioning to rain or a rain/snow mix.

&&

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

A highly amplified pattern is expected next week with a series of
strong lows forecast to track across the region. Forecast
confidence remains above average as models continue to be
relatively consistent with the depiction of several strong
synoptic features. Tuesday morning, a weakening low centered near
the eastern Aleutians may bring a period of storm-force gusts
through the islands and to the Alaska Peninsula through early
Wednesday. Strong cold advection on the back side of the low will
help to mix down strong winds aloft and support snow showers and
periods of low visibility conditions as the low tracks east. Model
solutions appear slightly north of where they were yesterday and
in greater agreement with regards to the track of the low. This
would take it along a similar track to the low centered near the
southern tip of the Alaska Peninsula this evening. Precipitation
spreads into southern mainland Alaska on Tuesday as the low pushes
its front northward. The air mass out ahead of the low should be
sufficient to keep all precipitation snow for inland locations.
Along portions of the north Gulf coast, rain may be possible at
low elevations, especially on the east side of a weak triple point
low that looks to develop in the northern Gulf. Precipitation
gradually tapers off going into Wednesday as the main source of
moisture is shunted eastward and the broader upper-level trough
begins to lift out of the area.

Out west, a low near Kamchatka, potentially as deep as 940 mb,
pushes a storm force front into the western Aleutians on Tuesday.
Along with it comes a southerly push of warmer air, which should
quickly switch precipitation from snow to rain. The front sweeps
to the eastern Aleutians by Wednesday, but uncertainty grows
thereafter. Models begin to disagree on whether the front stalls
out or is able to push into Southwest Alaska Wednesday night. Both
GFS and EC favor an eastward progression, and if it materializes,
the warm air moving in over cold air at the surface may be
sufficient to produce a period of freezing rain along the Bristol
Bay coast, while the rest of the area would see snow. Both models
keep the front progressing into Southcentral, where it has the
potential to bring several inches of snow on Thursday, but this is
lower confidence. Various shortwaves rapidly lift out ahead of
the deep low as it decays over the western Bering Sea on Thursday
and Friday. While there is significant uncertainty with the
placement of these features, models are in rough agreement on the
potential for a second, weaker front to sweep across the
central/eastern Aleutians/Bering Sea to the southern mainland,
bring mostly snow, with low potential for rain/mixed
precipitation near the coast. Though timing and placement is
uncertain, Southwest Alaska is the most likely area for this
front to bring precipitation, with lower confidence of moving on
into Southcentral for the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 130-131 136-139 141 150 160
					165 179-180 185 411-412 414.
         Storm Warning 130-131 177.
         Gale Warning 119-120 132 136-139 141 150 155 160 176 178
					351-352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KC
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...CQ