Small Craft Advisory 166, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 PM AKST Sat Feb 25 2023

.ANALYSIS AND UPPER LEVELS...

Fast zonal flow aloft is in place over the Alaska region with the
core of the jet stream across the southern Bering Sea then dipping
south of the Alaska Peninsula. A series of short-waves are embedded
within the westerly flow. One larger trough is exiting eastward
across the Gulf of Alaska, while smaller scale weaker waves cross
Southcentral. Weak cold air advection with these waves is
producing gusty winds along and through area mountain ranges, with
the strongest winds through bays and passes along the Gulf and
Prince William Sound coasts. Areas of dense fog and stratus were
widespread across the western Kenai/Anchorage/Mat-Su areas this
morning, but the sun has largely eroded it bringing full sunshine
to most of Southcentral.

A stronger short-wave and surface low are crossing the eastern
Bering Sea. The surface low is quickly weakening near the
Southwest Alaska coast while the short-wave digs east-southeast
across the Alaska Peninsula. A strong jet at all levels combined
with low level instability and the passage of the upper short-wave
is leading to strong gusty winds across the Eastern Aleutians and
southern Alaska Peninsula. A High Wind Warning is in effect until
9pm for the southern Alaska Peninsula, where winds will accelerate
through bays and passes. Some light snow with this system is
pushing onshore of Southwest Alaska while a mix of rain and snow
can be found across the eastern Aleutians and Alaska Peninsula.
Out west, a warm front is lifting northward from the northwest
Pacific to the western to central Aleutians, producing widespread
light rain and snow.

&&

.MODEL DISCUSSION...

Models are in good agreement with large scale features through
Tuesday. Of note, after a couple days of model inconsistencies
there is much better agreement in the development and track of a
deep low across the Bering Sea Monday through Tuesday. There are
some differences Tuesday afternoon through Tuesday night with
development and track of a triple point low in the western Gulf.
This will impact extent of easterly downslope flow across the
Kenai and western Chugach Mountains. There is also a short-wave
trough crossing the North Pacific which looks like it will
interact with the storm system over southern Alaska. Timing of
interaction will be key to how it impacts the forecast, so will
continue to closely monitor model solutions in the coming days.

&&

.AVIATION...

PANC...A weak digging short-wave and associated flow will result
in an increase in low level northwesterly flow tonight. However,
the surface/near surface layer will still decouple from the
boundary layer. Thus, areas of fog and stratus could redevelop
tonight. With slightly less favorable conditions do not think it
will be as widespread as this morning. For now, have indicated
VCFG, but there is certainly a chance IFR/LIFR conditions could
move back over the terminal. Most likely, this would occur as
overall low level flow weakens after 12Z Sunday. Any low clouds
that do develop will erode by midday Sunday, very similar to to
today.

&&

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

An upper level trough is moving across Southcentral, bringing
with it a colder and drier airmass. Persistent outflow winds
through the favored gaps and passes will continue overnight
tonight as a result of a tightening pressure gradient at the
surface and cold air aloft. Over the Gulf waters, gusty north to
northwest winds will briefly subside tonight before ramping up
again on Sunday. Winds are expected to subside across the interior
and marine waters by Monday as the main trough axis lifts out of
the region. Meanwhile, skies will also clear out with calm winds
in the inland areas, allowing temperatures to drop back down in
the single digits to below zero. Areas of dense fog may return
again tonight as residual moisture in the boundary layer lingers
across Cook Inlet and the Copper River Basin.

An amplified ridge builds over the Alaska mainland for the rest
of Monday, while a rapidly developing low pressure system moves
into the western Bering Sea. The front ahead of low pushes into
Southcentral, bringing a return of moderate to heavy precipitation
and winds early Tuesday. There is some uncertainty, however, with
a triple point low forming along the front and the exact
precipitation amounts. With the exception of Kodiak Island, the
rest of the north gulf coast and interior region will likely see
snow as main precipitation type heading into midweek. Stay tuned
for further updates.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Tuesday)...

A weak surface low and its front continue to push inland across
Southwest Alaska. Associated snow showers will gradually taper off
through Sunday evening as the system dissipates. Gusty
northwesterly gap winds across the Alaska Peninsula will diminish
on Sunday morning. A respite from precipitation will come to an
end by Monday night as a strong front reaches the Southwest coast
from the Bering. The front will spread snow and elevated winds
from west to east across through Tuesday. Precipitation is
expected to fall as rain for the Alaska Peninsula. This system is
generally expected to linger over Southern Alaska beyond mid week.

&&

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

A surface front extends across the Western and Central Aleutians
this afternoon and will continue pushing eastward. The front is
expected to lift across the Pribilof Islands by Sunday evening,
bringing with it elevated winds and snowfall into Monday morning,
at which time snow should transition to rain. The front will
continue to track east to the Southwest coast through Tuesday. The
associated low center will track to the Western Aleutians on
Sunday night, with gusty winds up to storm force wrapped around
the low. The low is advertised to move up to the Northern Bering
by Tuesday morning and then toward Saint Lawrence Island by
Tuesday night. Broad westerly to northwesterly flow with this
system will maintain elevated winds across the entire Bering and
Aleutians through Tuesday.

&&

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

The defining synoptic feature by Wednesday morning is a low
situated about coastal Western Alaska, with another low formed at
the triple-point of the former in the western Gulf of Alaska. The
shape and placement of both the parental low and the triple-point
low are not well agreed upon by the deterministic models, however
discrepancies have diminished since yesterday's model runs.
Wednesday morning, the 12Z Canadian and Euro models have the low
center over coastal Southwest Alaska, with multiple defined
troughs producing higher winds along the AKPen and producing the
aforementioned triple-point low in the western Gulf. Wednesday
morning on the 12Z GFS, the low is still offshore from Southwest
Alaska, with less defined frontal boundaries, suggesting less
intense winds along the AKPen and the triple point low has yet to
spin up. However, Wednesday morning represented by the 12Z GFS
appears to bring a widespread potentially heavy precipitation,
likely snowfall, event across Southcentral and Southwest. Impacts
to population centers such as Anchorage is difficult to determine
currently however, downslope flow will likely play a part in
mitigating snowfall for the Anchorage Bowl. This precipitation
wave is not advertised to be as intense by the Canadian and Euro
models, so we will need to wait to obtain a better idea once the
models converge on a solution. By Wednesday afternoon, the GFS and
Canadian runs come much more in-line, consolidating the trough to
the low in the Gulf and producing strong westerly and offshore
winds as the low moved east of Prince William Sound.

Precipitation will diminish across Southcentral by Friday and into
the start of the weekend. Transient showers look to linger in
Southwest Alaska Thursday and Friday with a weak wave to move in
Saturday morning. A resurgence of gusty winds out of the southern
gaps and passes of the Eastern Aleutians, AKPen, and near the Barren
Island Friday. Out in the Bering, a gale force low entering the
Western Aleutians will support the potential for Storm-force
gusts, and mild precipitation as it tracks into the Central
Aleutians Thursday afternoon, before dipping out to the south,
creating the aforementioned resurgence of winds on Friday. By
Friday afternoon, a new low appears to enter the Western Bering
bringing a sweeping front into the Western Aleutians. By Saturday
morning, this sweeping front looks to possibly merge with a North
Pacific low approaching the Central Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 181.
MARINE...HEAVY FREEZING SPRAY 121 126 127 128 129 130 139 141 160
180 181 185 414
GALE 130 131 138 150 155 165 170 174 175 176 177
178 179 180 181 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
LONG TERM...CL