Gale Warning 121, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
535 AM AKST Sun Feb 5 2023

.ANALYSIS AND UPPER LEVELS...

The jet stream extends from the western Pacific to the south of
the Aleutian Chain and into the southern Gulf of Alaska. Along the
jet, a shortwave trough and associated North Pacific low is
slowly entering the western Gulf. Light to moderate precipitation
with gusty winds are being reported in Kodiak Island. Offshore of
the coast, the latest ASCAT Passes is showing easterly small
craft to gale force winds stretching from Shelikof Strait to
Kamishak Bay. Meanwhile, a transient ridge is building over the
Alaska mainland with areas of dense fog covering the western and
northern portions of Anchorage. Out west, radar shows light snow
showers across western portions of Bristol Bay and the Kuskokwim
Delta in response an upper level wave lifting north and west over
the region. A complex low continues to move slowly east across the
Bering Sea, with multiple low centers spinning near the Pribilof
Islands. Colder air on the backside of the low is aiding gusty
northerly winds and convective snow showers over the western
Aleutians.

&&

.MODEL DISCUSSION...

The latest operational model runs are in decent agreement with
the placement and intensity of synoptic scale features at both the
surface and in the upper levels. The aforementioned Gulf low is
on track to move across Kodiak Island today and into the Cook
Inlet tonight. There are some positional differences as the low
lifts northeastward and uncertainty in snow amounts in the Portage
and Turnagain Pass areas.

&&

.AVIATION...
PANC...IFR to LIFR conditions continue through 05th/15z due to
low ceilings and restricted visibility. Conditions may change to
VFR after 05th/15z when ceilings rise and visibility improves.
Light winds will increase to northerly 10 kts gusting to 20 kts
around 05th/20z.

&&

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

Areas of fog across Knik Arm and northern Cook Inlet will
dissipate through the first half of Sunday morning as a frontal
system lifts to the northern Gulf coast and clouds overspread the
region. This front is attached to a deepening storm-force low
situated near Chirikof Island this morning. This low is expected
to move over Kodiak Island this morning to a position just east of
the Barren Islands by Sunday afternoon. As it does, a storm-force
front will drive to the Southcentral Coast with snow and gusty
easterly winds across the eastern Kenai Peninsula and Prince
William Sound. Gusty northeasterly winds are also expected to
develop this morning from the Matanuska Valley south to Kenai,
peaking around mid to late afternoon. The strong easterly winds
will likely lend to areas of blowing snow across the eastern Kenai
Peninsula, especially across Portage Valley and at higher
elevations. Strong easterly winds across Kodiak Island this
morning will transition to gusty west-southwesterly winds as the
low tracks north through Monday. Gusts approaching hurricane-force
are possible along just offshore of the southern and eastern
coasts of Kodiak Island late Sunday afternoon through early Monday
morning.

Widespread precipitation will also accompany the front and its
parent low as they both move northward through Monday. Snow in
Kodiak City this morning will quickly transition to rain as the
front lifts north, but not before an inch or so of snow
accumulation. Farther north, snow will overspread the Prince
William Sound area by mid-morning, with perhaps a transition to a
rain/snow mix for Whittier, Seward, and perhaps Portage as warmer
air advects in along the immediate coast. The heaviest
precipitation is expected late morning through early evening. A
Winter Weather Advisory is out for portions of the eastern Kenai,
with snow accumulations ranging from 8 to 14 inches through
Sunday night with locally higher amounts of up to 20 inches
possible near the Whittier Tunnel.

A brief period of light snow is also possible from Kenai to
Anchorage this afternoon before the southeasterly winds aloft
increase and keep most of the moisture from spilling over the
coastal mountains. An embedded upper-level wave may allow some
light snow to move over the Copper River Basin later today;
however, the bulk of the moisture will again remain confined to
the immediate coast and coastal mountains, with Cordova picking up
a few inches of snow before transitioning to a rain/snow mix with
strong east winds and Valdez seeing several inches of snow through
Monday.

By Monday, the low is expected to move up Cook Inlet, though the
exact track is still difficult to pin down. This track, however,
will allow moisture to move up the Inlet and overspread Kenai,
Anchorage, and the Mat-Su Valleys for Monday with a general one to
three inches of snow possible. Winds will also be gusty for
places like Homer and across Kamishak Bay Monday morning as the
system moves north and colder air wraps in behind the low. As the
low continues to track north, southeasterly winds are expected to
develop for Anchorage and across the Copper River Basin; however,
with colder air advecting over Southcentral in the wake of the
low, any lingering precipitation is expected to remain as snow.

&&

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

Broad complex system extending across the Bering Sea weakens over
the next couple of days. Remnant shortwaves passing over the
Kuskokwim Delta are producing periods of light snow across the
region this morning. A low pressure system moving out of the North
Pacific towards Kodiak Island is sweeping addition waves into
Southwest that will bring about another round of active weather.
Snow begins in Bristol Bay early this morning. North-
northeasterly winds will ramp up by mid- to- late morning,
resulting in areas of blowing snow and reduced visibilities. A
Winter Weather Advisory for Blowing Snow has been issued for
Bristol Bay, primarily affecting Dillingham and areas north to
Koliganek and east to Igiugig. Additional snow amounts of 3-4
inches is likely. Winds are expected to diminish tonight, with
light snow tapering off slowly through the overnight hours. Cold
air advection filters over Southwest Alaska on Monday. Anticipate
a drop in temperatures into the single digits Monday night and
Tuesday night.

&&

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

Generally unsettled weather over the Bering Sea and Aleutian
Chain over the next few days. The broad complex system that has
dominated the Bering Sea recently will continue to gradually
weaken, feeding energy to an incoming North Pacific low. Light
showery activity will continue across much of the area, with
areas of small craft winds and smaller areas of gale force winds.
Cold air advection enter the western Bering Sea and Western
Aleutians today, working westward over the next couple of days.
Anticipate larger areas of freezing spray and heavy freezing
spray, as well as periods of extreme freezing spray along the ice
edge through Monday.

&&

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

Confidence continues to remain high on both domains remaining
rather active with no real sustained quiet stretches with high
pressure firmly in control, but rather transient ridges between
systems; the only exception might be coastal southwest Alaska.
Southern Alaska still remains under the influence of a broad
negatively trough stretching southeastward from Siberia through
Thursday evening. This will yield continued precipitation for the
eastern Kenai Peninsula, Prince William Sound, the northern Gulf
Coast, as well as interior southwest Alaska. The western Kenai
Peninsula, Anchorage, Mat-Su Valleys, and Copper River Basin could
also see precipitation chances during the first half of the long-
term as well, but uncertainty exists with potential cross-barrier
flow issues. Meanwhile, there are signals that coastal Bristol
Bay, the Kuskokwim Delta, and lower Kuskokwim Valley could see
quiet weather Wednesday morning through Thursday night as ridging
moves overhead. However, guidance agrees that conditions return to
being unsettled as a deep Bering Sea low sends multiple fronts
and shortwaves eastward into the coast early Friday morning
through at least Saturday. There is also agreement that the front
and shortwaves will begin to affect Southcentral Alaska Friday
morning with Kodiak Island the first to see precipitation, before
the active weather moves northward to the Kenai Peninsula, Prince
William Sound, and the northern Gulf Coast through Saturday
morning.

The aforementioned strong Bering low looks to first approach and
impact the western Aleutians and western Bering Sea Wednesday
evening and last through much of the long-term with winds at
least low-end storm-force. Multiple fronts and shortwaves move
eastward across the central Aleutians/Bering and eastern
Aleutians/Bering Thursday morning through Friday morning.
Confidence is growing that this could be an impactful storm system
for the Bering Sea and Aleutians with heavy precipitation and
strong winds.

There is uncertainty towards the end of the long-term as guidance
is struggling with how to handle the evolution of an additional
North Pacific low and its eventual track. The Canadian guidance is
the most aggressive with quickly developing this low to storm-
force and accelerating it into the central Bering through
Saturday, while the GFS and ECMWF are less aggressive with the
evolution and have a further eastward track with this feature into
the extreme southwestern Gulf of Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 125, 161
MARINE...Storm Warning: 119, 130-132, 138
		 Gale Warning: 120, 125, 136, 137, 139-141, 150,
         155, 175-177, 351-352, 411, 142.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MF
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...DAN