Gale Warning 861, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Fri Dec 30 2022

.ANALYSIS AND UPPER LEVELS...

Longwave trough pattern continues, with multiple embedded low
pressure systems moving across the Bering Sea, Gulf of Alaska, and
northern Pacific. There is some remnant surface rotation near
Kodiak Island today, weakening through the morning and
dissipating. Lingering precipitation along the north Gulf coast
will persist through this morning. A system in the north Pacific
is tracking towards Kodiak Island, the associated front moves into
the southern Gulf tonight. Another north Pacific low tracks well
south of the Aleutian Chain over the next couple of days before
pushing into the southwestern Gulf. Its front moves into the Gulf
on Saturday and travels northwards. Enhanced easterly winds along
the north Gulf coast are expected by Saturday afternoon, along
with widespread precipitation into Southcentral (primarily along
the coast, including Kodiak Island, and eastern edges of the
western Alaska Range.

&&

.MODEL DISCUSSION...

Models are doing alright through the first 24 hours. There is a
decent handle on the weakening low south of the Alaska Peninsula
(AKPen), the low north of Amchitka that is merging with a North
Pacific low, and a fair handle on the trough pushing northwards
across the Gulf of Alaska. There is still quite a bit of
disagreement with the North Pacific low moving south of the
Aleutian Chain towards the Gulf through the weekend. There is an
agreed upon general consensus for overall track of the system, but
varying strengths, speeds, and center location across all models.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is a
chance for a period of snow later this morning with cloud
ceilings dropping below 5000 ft. Conditions should improve again
by early evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/This
morning through Sunday afternoon)...

A broad upper level low over the western Gulf will continue to
lift several upper level waves over the northern Gulf and into
Southcentral today. These waves will work to displace an upper
level high over the interior, setting the stage for a larger low
to arrive by the weekend. For today, expect continued
precipitation concentrated over Prince William Sound and the
eastern Kenai Peninsula. By later this afternoon, a stronger
upper level wave lifts northward, and this may produce a few snow
showers farther inland, including over the Copper River Basin and
the Susitna Valley.

By Saturday morning, a strong North Pacific low races across the
Pacific from west to east south of the Aleutians; aided by a 180
knot jet at 300 mb. Along the way, it picks up a thread of
tropical moisture and transports this warmer airmass into the
Gulf. As this strengthening low nears the western Gulf Saturday
morning, it phases with the existing, weaker low currently south
of the Alaska Peninsula. This complex system will ultimately drive
the weather through the weekend.

By Saturday afternoon, this deepening low is expected to be
centered just south of Kodiak Island, though models continue to
struggle with exact placement and strength. The NAM and Canadian
models keep the strongest solution, advertising anywhere from a
948mb to 955 mb low, while the GFS depicts 960 mb. As the low
gradually tracks northward, the associated frontal boundary will
produce storm force easterly winds across the Gulf, reaching the
northern Gulf coast by Saturday night. Noticeably stronger
northerly winds will begin to occur across the Cook Inlet area
late Saturday, and then will continue to pick up during the
overnight hours through early Sunday. Meanwhile Turnagain Arm,
Passage Canal, and Portage Pass will see gusty easterly winds
ramping up Saturday night. In addition to strong easterly winds,
this front will introduce a warm, moist airmass, as southerly to
southeasterly mid level winds accompany this system.

Given the fetch of moisture this storm brought into the Gulf, we
have high confidence it will produce ample precipitation across
Southcentral. We also have moderate confidence that the period of
most impactful weather will occur on Sunday for mainland
locations. However, precipitation types still remain quite the
challenge. Coastal locations will see rain, with heavy rain
beginning over Kodiak Island Saturday afternoon. There is
increasing confidence that the western Kenai Peninsula will see
freezing rain. The toughest locations to narrow down expected
precipitation type include Anchorage Bowl, Mat-Su Valley, and the
southern portion of the Copper River Basin. While precipitation
may start as freezing rain in these locations, it's possible there
will be a change to all rain as relentless warm air advection
continues most of the day Sunday. Please continue to check
frequently for updates as we work to refine the details.

&&

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

Driving the current weather pattern across Southwest this morning
is a complex low situated over the Eastern Aleutians. Rotating
around this low are three smaller lows, with all three lows
promoting areas of cloud cover and light precipitation within
their respective areas, from south of the Eastern Aleutians, to
Kodiak Island, and a third low west of the Pribilofs. With the
exception of light snow pushing across interior Bristol Bay this
morning, Friday should remain quiet for Southwest Alaska with calm
winds forecast for all but portions of the Kuskokwim Delta, where
northeasterly winds will gust into the low to mid 20's through
the afternoon hours.

The complex low over the Eastern Aleutians is forecast to
strengthen and become better organized over the weekend, which
will see a bit of a pattern change Saturday into Sunday. As low
pressure strengthens, a tightening pressure gradient on the north
side of the low will result in potential 30 to 40 mph easterly
winds spreading out of the Kamishak Gap and into Bristol Bay with
gusts of 50 to 60 mph possible by Saturday night. This will be
coincident with a round of light snow late Saturday night/early
Sunday morning. Blowing snow is forecast with reduced visibility
through the morning hours on New Year's. Temperatures from King
Salmon to Iliamna and points southward will likely see
precipitation quickly transition to rain, with the biggest threat
for blowing snow and reduced visibility encompassed by an area
from Naknek to Dillingham to Koliganek. Finally, as the organized
upper low wobbles from near Kodiak Island back into the Bering
over the course of the day on Sunday, winds and any lingering
precipitation will begin to diminish across Southwest Alaska.

&&

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

A ridge of high pressure continues over the Seward Peninsula this
morning while a complex low is positioned further south and over
the Central and Eastern Aleutians. A series of troughs are
expected to rotate around the complex low, lifting northward into
Southwest Alaska through the weekend. High pressure is forecast to
retreat northward as a result while low pressure becomes better
organized over the North Pacific on Saturday. Models are coming
into better agreement with the development of a stronger and more
organized upper low tracking cyclonically across Kodiak Island and
into Southwest by Sunday, with broad cyclonic flow stretching
across the entirety of the Bering.

Ultimately, this will result in small craft northerly winds
staying confined to the western and northern Bering through today,
with some gales possible over the Western Aleutians over the
latter half of the day. Significant wave heights in the mid to
upper teens will exit the western Bering through tonight. As low
pressure becomes more organized south of Kodiak Island, easterly
flow at the surface will allow small craft winds and higher gusts
to spill into Bristol Bay and the eastern Bering through Saturday
night. By Sunday, a broad swath of northerly small craft winds
will blanket the Bering from Saint Matthew Island into the
Aleutian Chain. Rough seas of 8 to 12 feet will be common. Any
shower activity across the Eastern Aleutians is expected to fall
as rain through Saturday while further west a mix of rain and snow
will be possible. Colder temperatures will advect across the
Aleutians on Sunday, with snow becoming the predominant
precipitation type across the Western Aleutians and a mix of rain
and snow expected to develop over the Central and Eastern
Aleutians.

$$.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

Going into next week, the low centered near the AKPEN that is
forecast to bring this weekend's mixed precipitation event to
Southcentral will begin to weaken, with the most impactful weather
coming to an end. Though the low's occluded front will likely have
pushed inland by Monday, upslope precipitation will linger along
much of the Gulf coast as southerly flow continues to wrap around
the weakening low. Scattered, showery precipitation will also
likely continue in Bristol Bay and along the Alaska Peninsula in
the vicinity of the low center. Some mixed precipitation may
linger with this system into Monday as well. Inland locations dry
out by Tuesday morning. Later on Tuesday, a potentially gale-force
low enters the eastern Gulf of Alaska and tracks toward the
western Gulf coast. This low does not look to bring as much
precipitation, warm air, or winds as the weekend low, and its
impacts are most likely to be focused between Kodiak Island and
the eastern Kenai Peninsula Tuesday night into Wednesday. Some
light overrunning precipitation may move in over Southwest Alaska,
but it is likely to be all snow. As the low weakens into Thursday,
southern mainland Alaska looks to dry out with weak flow and no
major source of moisture available.

Out west, northerly flow prevails across the Bering Sea, with
scattered snow showers across the Aleutians through Tuesday. Then,
a large upper-level low supported by a cold air mass moving out of
East Asia begins to push into the western Bering. It is led by a
front, which appears to bring mostly snow to the western and
central Aleutians through Tuesday night, given the primarily zonal
orientation of the Pacific jet and resulting relatively weak tap
of subtropical warm air. As it pushes through, several weak waves
embedded in the broad low propagate into the Bering, keeping
relatively cold air in place and bringing periodic chances for
snow reaching as far as the eastern Bering/Aleutians by Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 130-132 138 139 150 178 351 352 411
		 Heavy Freezing Spray Warning: 180 185
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
209 PM AKST Fri Dec 30 2022

AKZ101-111-121-125-131-135-171-310015-
Anchorage-Matanuska Valley-Western Kenai Peninsula-
Western Prince William Sound-Northeast Prince William Sound-
Southeast Prince William Sound-Kodiak Island-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, Chickaloon, Kenai, Soldotna, Homer,
Cooper Landing, Whittier, Seward, Girdwood, Moose Pass, Valdez,
Thompson Pass, Cordova, and Kodiak City
209 PM AKST Fri Dec 30 2022

...STRONG LOW TO BRING WINDS AND WINTRY MIX TO SOUTHCENTRAL THIS
WEEKEND...

We continue to monitor the potential for an impactful weather
event to occur across Southcentral this weekend.

A storm-force low will enter the northern Gulf of Alaska Saturday
afternoon through the evening, bringing a storm-force front first
to Kodiak Island, then to the northern Gulf, including Prince
William Sound and Passage Canal on Sunday. Gusty easterly winds
are likely through Portage Valley and Turnagain Arm, beginning as
early as Saturday night.

Accompanying this area of low pressure is a deep fetch of
moisture which will also introduce warmer temperatures. This will
likely result in a wintry mix of precipitation including rain,
snow, freezing rain, sleet, or a combination of all throughout the
event. Weather models are still struggling to resolve forecast
details, and precipitation type remains the biggest challenge.

At this time, we are confident that the front will begin to impact
Kodiak Island Saturday afternoon, and the southern Kenai
Peninsula Saturday night into Sunday morning. As this system
lifts northward, it will then affect the Anchorage Bowl, Matanuska
Valley, and southern Copper River Basin during the day on Sunday,
when the bulk of precipitation is expected to occur.

Please monitor the forecast closely. We will be making frequent
updates as we work to refine these details, especially regarding
precipitation type.