Gale Warning 2, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKST Fri Dec 31 2021

.ANALYSIS AND UPPER LEVELS...
A series of short-wave troughs are tracking south to eastward
across mainland Alaska and the eastern Bering Sea, one over the
Interior, one over Southcentral, and one along the Alaska
Peninsula. Patchy light snow can be found over Southwest Alaska,
with steady widespread snow over Southcentral Alaska. At the
surface, a triple point low has deepened out ahead of the short-
waves and is crossing the northern Gulf of Alaska. Cold air
advection out ahead of the northern-most short-wave is moving
into Southwest Alaska, with gusty northerly winds developing from
the Kuskokwim Valley to the Kuskokwim Delta. Out west, a ridge
of high pressure is centered over the central Bering Sea and
Aleutians. A storm is tracking up the west side of this ridge,
bringing gale to storm force winds and rain to the far western
Aleutians.

&&

.MODEL DISCUSSION...
Models are in good agreement with handling of the large scale
pattern over the next few days. High resolution models will be
heavily used for the ensuing cold air advection wind event over
southern Alaska this weekend, as they have a much more accurate
representation of winds through the many gaps/passes/valleys
across the region.

&&

.AVIATION...
PANC...Snow and MVFR to IFR conditions will persist through this
evening. Conditions will then improve as snow ends - no later than
09Z. Much more significant improvement in ceiling will arrive 12Z
to 15Z as cold air advection and gusty northerly winds move into
the area. Winds will strengthen through the day Saturday and peak
Saturday night into Sunday as high winds come out of the Matanuska
Valley and down Knik Arm right into the Anchorage terminal. There
is high confidence is reaching at least 35 kt gusts during the day
Saturday. There is potential for wind gusts to reach as high as
45 to 55 kt on Sunday if the core of strongest winds in the Mat
Valley comes directly down to Anchorage.

&&

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

A couple of upper level troughs will swing through Southcentral
tonight and Saturday which will keep areas of snow likely across
much of the area tonight with another 1 to 2 inches of snow
expected across Anchorage, the MATSU valleys, as well as the
Copper River Basin. With higher amounts near Cordova of up to 6
inches, and the hillside of Anchorage as well as Eagle River
where 2 to 4 inches are possible through Saturday morning.

The big story will be the winds and cold air which will move into
the area tonight and Saturday as the upper level trough and
surface low move out into the Gulf. This will bring arctic air
from the north which will tighten up the pressure gradient and
funnel winds through the gaps. The usual areas will see the gap
winds, however expect very cold air to spill through the MAT
valley and create strong winds up to 75 mph beginning Saturday
afternoon and continuing through Sunday evening therefore a high
wind warning has been issued for the MAT Valley. These winds are
expected to bend down along the Knik Arm and into the northern and
western parts of Anchorage Sunday where we could see wind gusts
as high as 60 mph, for this reason a high wind watch has been
issued for the Anchorage area from Sunday morning through early
Sunday evening. Additionally, strong winds will blow through the
Susitna and Copper River Basin from the north creating conditions
favorable for wind chill advisories. Winds will also be strong
around Thompson Pass but expect them to stay around 65 to 70 mph.
With strong winds and cold air spilling across Thompson Pass a
wind chill advisory has also been issued from Saturday afternoon
through Sunday evening. Valdez will get some stronger winds with
gusts up to 55 to 60 mph possible. The winds will also be strong
across Kodiak Island with gusts of 60 to 70 mph possible. With the
very cold air spilling across Kamishak Bay and Shelikof Strait
expect Hurricane Force winds on Saturday with heavy freezing spray
which will cause dangerous conditions for Mariners.

Finally with the cold air moving across the area, bands of snow
showers will develop near Kodiak Island and its coastal waters
which could bring areas of snow and blowing snow Saturday
afternoon and Sunday. Blowing snow is also possible across parts
of the Susitna valley and Copper River Basin Saturday into Sunday
as wind blows around the recent snowfall. Monday expect clear and
cold conditions with the winds slowly weakening.

&&

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

Residual precipitation with a trough is moving south through the
AKPen this afternoon with cold air advection and strong northerly
and clearing skies following closely behind. High temperatures for
today were realized before sunrise. Model agreement is high that
mid level temperatures will drop an additional ten degrees over
the next 24 hours and stay in place over the next few days. The
upper jet extends from the lower Kuskokwim Valley to west Kodiak
Island. Unidirectional flow aloft and a tightening pressure
gradient will allow cold winds to mix to the surface that could
cause dangerously cold wind chills of around 40 below for the
interior Bristol Bay and as far south as King Salmon on Saturday
and Sunday night. A Wind Chill Advisory has been issued for this
area. This general weather pattern will combine with clear skies
Sunday night, promoting the coldest wind chills into the beginning
of the week.

&&

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

A trough is moving south of the AKPen this afternoon with cold
air advection and strong northerly flow over the eastern Aleutians
to western Kodiak Island. Unidirectional flow through the gaps
will accelerate winds to storm force by tomorrow morning near Sand
Point and Chignik and increasing to hurricane strength at times
south of the AKPen on Saturday. Looking west, a high amplitude
ridge is firmly in place and blocking much of the movement of the
low pressure systems to the east and west of the Central Aleutians
and Bering Sea. An upper low developing near the AKPen on Monday
morning will attempt to dig at this ridge and the upper pattern
may retrograde slightly. With an overall blocking pattern in
place, a front to the far west will be nearly stationary and will
bring rain to the western Aleutians for the next few days. Rain
will struggle to make it east of Amchitka.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Bering...Along the southwestern edge of high pressure in the
Bering Strait on Monday, a widespread swath of easterly gales
blows across the central and western Bering/Aleutians before
diminishing Monday night. Seas approach 30 ft accompanying the
strong gales on Monday, but subside to near 20 ft by Tuesday
afternoon. A smaller area of northeasterly gales near the
Kuskokwim Delta and Bristol Bay on Monday shift into the northern
Bering by Tuesday morning and then diminish. Gale force gap winds
south of the Alaska Peninsula also diminish Monday night. Tuesday
afternoon a broad trough with embedded lows over the North Pacific
induces another round of easterly gales from Bristol Bay into the
central Bering through Wednesday. By Wednesday morning, seas begin
to build to 20 ft in the central Bering.

Gulf of Alaska...The strong gap winds expected Saturday and
Sunday begin to diminish by Monday, with localized areas of gales
continuing to linger beyond Monday afternoon, particularly near
Kamishak Bay and Shelikof Strait as low pressure exits into the
North Pacific. A front moves north into the Gulf on Tuesday
afternoon, allowing widespread easterly gales to develop in the
southern Gulf. Gale force winds may also develop through the
Barren Islands and southern Cook Inlet and persist through
Wednesday. Seas build to near 20 ft by Wednesday morning in the
far southern Gulf.

&&

.LONG TERM FORECAST (Days 4 through 8: Tuesday through
Friday)...

Tuesday marks the beginning of a pattern shift as there is general
model consensus that a strong amplified upper level ridge sitting
over the Bering this weekend shifts northward into the Chukchi
Sea. A large closed upper low to the east of the ridge, over the
western Gulf of Alaska, begins to pinch off the ridge on Tuesday,
retrograding along its southern periphery into and across the
Bering. Ahead of the low, a blast of cold, Arctic air, previously
sitting over the Alaska mainland, is pushed across the Bering,
creating widespread snow showers and the potential for freezing
spray, especially near the Southwest coast. Various surface lows
look to move northward from the North Pacific and push a broad
front across the southern Gulf, AKPEN, and the Aleutians, leading
to a return of warmer, wetter conditions there by Wednesday. The
bulk of the warm, moist air looks to remain confined there as the
strong ridge to the north keeps the front stalled out, leaving
Southwest and Southcentral Alaska colder and drier. Weak warm
advection on the back side of the upper low nonetheless allows a
bit of a warm-up and lighter winds over the Alaska mainland
through the week.

Both GFS and the EC indicate that by Thursday stronger upper-
level ridging extends further south over mainland Alaska, likely
keeping the area clear and dry. GEM, despite a further west
placement of the strong upper-level anticyclone also indicates the
same general northwest to southeast ridge axis, which is more
prone to draw surface lows northward into the Bering. Both GFS and
GEM indicate the potential for a surface low to draw warm, moist
air deeper into the Bering and possibly into Southwest Alaska by
the end of the week. In this setup, temperatures may warm to near
or above freezing across parts of Southwest late Friday.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND CHILL ADVISORY: 145 & 161.
         HIGH WIND WARNING: 111.
         HIGH WIND WATCH: 101.
MARINE...Hurricane Warning: 130, 138, 150
         Storm Warning: 119, 127, 131-132, 136, 139, 155, 178, 352
         Gale Warning: 120-121, 125-126, 128-129, 137, 140-141, 160,
         165, 170-172, 174-177, 180, 351, 413, 414
         Heavy Freezing Spray Warning: 119, 121, 126-132, 136-139,
         141, 150, 160, 165, 180, 181, 185, 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...RC/CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...CQ