Small Craft Advisory 1014, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
551 AM AKST Thu Dec 22 2022

.ANALYSIS AND UPPER LEVELS...

At upper levels, a large blocking ridge continues to build over
the Chukchi Sea while extending southeast into the Alaska
Mainland. A long-wave trough stretches across the North Pacific
and has multiple shortwaves embedded within the flow. An
impressive tropical moisture feed from the Pacific (east of
Hawaii) is promoting a moisture-rich environment across the Gulf,
Alaska Peninsula, eastern Aleutians, and Bering Sea.

At the surface, cold and generally dry conditions persist across
much of southern Alaska, where temperatures in the -20s and -30s
remain the norm for portions of the Copper River Basin, Mat-Su
Valleys, and Lower Kuskokwim Valley. A deep low currently
centered about 220 miles south of Sand Point extends its large
occluded front across the eastern Aleutians, Alaska Peninsula,
Kodiak Island, and Gulf of Alaska. Precipitation with the front is
primarily rain, but the eastern Kenai and western Chugach
Mountains are seeing some light snow due to upslope flow and
overrunning. The snow will taper off this morning. Out west, a
stationary front drapes across the eastern Aleutians and most of
the Bering Sea, maintaining steady heavy rain for the eastern
Aleutians and snow for the Pribilof Islands. A Flood Warning
remains in effect for the eastern Aleutians (Unalaska area) as
heavy rainfall creates urban area and small stream flooding.

Strong winds are currently a theme across portions of the west
and east domains. Widespread easterly gale to storm force winds
blanket the Gulf, Alaska Peninsula and eastern Aleutians, and
Bering Sea.

&&

.MODEL DISCUSSION...

Models are in overall good synoptic agreement through Friday,
after which time forecast confidence begins to decrease as models
struggle with the evolution of a Gulf surface low. There is
general consensus that the low will linger along the north Gulf
coast roughly Saturday morning through Sunday morning before
dissipating. However, the eventual track and positioning of the
low will ultimately impact the precipitation and wind forecast
along the north Gulf coast. Out west, there is good agreement that
the stationary front over the Bering and eastern Aleutians will
finally begin to decay Friday into Saturday.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period.
Northerly winds will hold fairly steady below 12kts until
tonight/Friday when stronger northerlies will develop as cold air
advects across the region.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Thursday through Saturday night)...

The weather across Southcentral will be dominated by two distinct
features over the next several days. First, a stout polar high
situated over the Al-Can border will keep an arctic airmass in
place across interior Southcentral with generally clear and very
cold temperatures. The exception, however, is a band of cloud
cover and some widely scattered precipitation along the immediate
coast. This is due to a weak trough draped over the northern
Gulf, out ahead of the second feature. This second feature is a
frontal system over the southern Gulf, attached to a storm-force
low south of Kodiak Island. Strong southeasterly flow along and
ahead of the front, driven in part by the pressure and thermal
gradients between it and the aforementioned high, is bringing rain
and very gusty wind to Kodiak Island this morning and will
continue to do so through the day before the low moves west and
the front lifts north into the Gulf.

The front will slow and stall as it lifts north, due to a vigorous
upper-level wave dropping south into the interior of the state from
the arctic.This upper-level wave will reach its southern extent
over the Mat-Su Valleys and Copper River Basin Friday morning
before sliding over Southwest Alaska and elongating. This feature
will usher in a reinforcing shot of arctic air over the region
with 850mb temperatures dropping below -30C over the Copper River
Basin and between -15C and -25C elsewhere. The combination of cold
air advection, dense arctic air, and the pressure gradient the
aforementioned ridge and surface low will trigger a strong
drainage flow out of gaps and passes. The Matanuska Valley looks
to be the bullseye for strong winds, with winds increasing quickly
late Thursday evening, peaking Friday, before slowly winding down
Friday night through Saturday. Gusts to 65 mph are possible for
the Matanuska Valley with this event, and the combination of winds
and transportable snow on the ground could lead to blizzard
conditions at times, especially early Friday morning. Gusty
north-northeasterly winds will likely result in blowing and
drifting snow for many other locations including, along the Parks
Highway from Talkeetna north, along the Glenn Highway from Eagle
River to north and west Anchorage, and along the Sterling Highway
from west of Soldotna south to Anchor Point.

Strong winds are also likely for channeled terrain in the Copper
River Basin and through Thompson Pass down to Valdez. For the
Copper River Basin and Thompson Pass, the combination of winds and
very cold temperatures may lead to wind chill values as low as -60F
and -50F, respectively.

The winds will begin to wind down on Saturday as a new surface
low spins up on the front and moves north to the Southcentral
coast. While winds along the coast may persist due to the
continued tight pressure gradient, temperatures are expected to
moderate as clouds and snow move into Prince William Sound and
the Copper River Basin. Right now, it looks as if this feature
weakens as it runs into the eastern Kenai Peninsula coast, with
little to no chance for snow west of the coastal mountains.

&&

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

High pressure continues to build into Southwest Alaska while
simultaneously a North Pacific low and its associated front lift
northward towards the eastern Aleutians early this morning. High
winds due to tight pressure gradients between the two
aforementioned features, have impacted the Alaska Peninsula with
gusts reaching up to 65 knots last night and are expected to
persist through early this morning. As a result, a High Wind
Warning has been issued for the Alaska Peninsula, including the
cities of Cold Bay and Sand Point, and will expire this morning at
6 AM AKST. Winds will slowly relax throughout today as the
aforementioned front and low track westward. Most of Southwest
will stay dry from this frontal passage, but the exceptions will
be the Alaska Peninsula and portions of Bristol Bay. Bristol Bay
should remain all snow today with precipitation ending tonight,
but the Alaska Peninsula could see a rain/snow mix today with
precipitation chances lasting for the next several days. Colder
conditions will make its way back into the area for Friday and
into the weekend along with elevated northerly winds.

&&

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

Active weather will continue for the Bering and Aleutians for the
next several days. An atmospheric river continues to orient
itself right at Dutch Harbor/Unalaska resulting in a Flood Warning
remaining in effect until Friday morning. The heaviest rain over
the central and eastern Aleutians will taper off this
morning/afternoon as a North Pacific low tracks across the Chain
and westward into the Bering Sea. Wind gusts of 60 to 65 knots
have been reported over the Alaska Peninsula and portions of the
eastern Bering early this morning. Gusty conditions will continue
throughout the central and eastern Bering with a swath of easterly
storm-force winds continuing along the Bering and Pacific side of
the Alaska Peninsula throughout today. Winds will slowly diminish
to gale-force tonight and through the rest of the short-term.

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

It is becoming more clear that an upper level low will split off
of the cold trough over the mainland part of the state and set up
over the Eastern Aleutians/Alaska Peninsula by Sunday. Once this
upper level pattern is established, it will not change much
through the middle of next week. The result will be temperatures
generally returning to more seasonal levels with it colder in the
Bering Sea region and warmer over mainland Southern Alaska.

A surface low should be in that eastern Aleutian/Alaska Peninsula
region vertically sacked with the upper level low early through
middle of the week. This will not be a strong low but will keep
some clouds and precipitation in the area. The strongest low early
next week will be in the Gulf of Alaska Sunday into early Monday.
While most of the coast will see this precipitation in the form
of snow, areas around southern Prince William Sound may have
periods of rain. We will just have to watch the development of the
storm to see whether the warmer temperatures make it to the coast
or not.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning: 111.
		 High Wind Warning: 181.
   		 Flood Warning: 185.
		 Wind Chill Advisory: 131, 141.
MARINE...Storm Warning: 130-132, 138, 180, 351, 352, 414.
		 Gale Warning: 119, 120, 125, 127, 128, 136, 137, 139, 140,
					   150, 155, 160, 165, 170-172, 174, 179, 181,
                       185, 411-413.
		 Heavy Freezing Spray: 127, 130, 139 140, 180, 181, 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...EZ