Small Craft Advisory 263, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
547 AM AKDT Thu Mar 24 2022

.ANALYSIS AND UPPER LEVELS...

Broad upper ridging in the North Pacific combined with low
pressure in the Gulf is leading to a cold, northwesterly flow in
across much of the Bering. This is bringing scattered rain/snow
showers over the Aleutians, enhanced by cold temperatures aloft
and a number of shortwave troughs. While much of Southwest Alaska
remains dry, a few light snow showers are seen in the Bristol Bay
area near an upper low. A relatively strong front currently
extends across the northern Gulf coast. Snow and blowing snow is
expected to begin shortly over Kodiak. Widespread snow showers are
tracking across the Kenai Peninsula as well and will continue to
move northward. The main southerly fetch of moisture stretches
all the way down to the Pacific Northwest. Heaviest precipitation
looks to remain near higher terrain along the coast.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement. The latest GFS has come
more in line with other models tracking an incoming Gulf low
farther north over Kodiak Island. However it does still show a
second closed compact circulation and consequently higher winds
in the northern Gulf on Friday morning. Also, subtle differences
in the position of the low over Kodiak lead to some uncertainty in
precipitation type timing/amounts there today. Conditions become
much quieter by this weekend.

&&

.AVIATION...

PANC...VFR conditions will persist. Winds remain somewhat tricky,
but look at this point to remain north over the terminal through
Friday morning, gusting up to 20 kt this afternoon. Southeasterly
Turnagain winds may lead to low level shear this morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Thu
through Sat)...

The main themes will be the continuation of snow for higher
elevations near the Eastern Kenai Peninsula, strong winds, and
slowly warming temperatures. The initial wave of the active storm
track moved over the area last night. This helped to establish
deep southeast flow stretching from the Gulf up through the
Anchorage Bowl. Temperatures near sea level (Portage, Whittier,
Cordova) have stayed right around freezing which has limited
accumulation to some extent. In the mountains however, it is a
different story with the mid slopes of Alyeska already picking up
over 15 inches since Wed morning. Some instability helped to ferry
some snow showers over the Chugach and into Anchorage Wednesday
evening causing some minor accumulations.

This will continue to be the story for the next several days. The
first upper level wave will push into SW AK today, but it will be
immediately replaced by a stronger system in the Gulf. This system
will cause a period of moderate to heavy snow for Kodiak before
temperatures warm enough there this afternoon to transition to all
rain. As it presses up against the Gulf Coast, east to southeast
winds will ramp up to storm force later today. These winds will
move through Prince William Sound and bring gusts to 50 mph into
the Portage Valley. Overnight, the system trended a bit farther
north and a bit stronger. This should lead to higher QPF amounts
with a better orientation to the upslope flow near the Portage
Valley/Girdwood.

As the system drives north, it will bring up some warmer air. This
should allow snow levels to slowly rise to between 500-1000 feet
near Turnagain Pass. But with intense precipitation rates
associated with some instability, colder air being dragged down
from aloft will help to keep the levels from spiking too high. For
inland areas, downsloping will persist and keep most of the
population centers mostly dry. The downsloping winds will also
allow for continued above normal temperatures with Anchorage
climbing into the low 40s. As we march into the weekend, the
intensity of the precipitation/storms for Western Prince William
sound should diminish, but we still expect linger snowfall in that
area through Saturday.

&&

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

An unsettled but benign weather pattern is expected across
Southwest Alaska over the next few days. There is a chance of
snow showers across the eastern lower Kuskokwim Valley and Bristol
Bay Thursday morning through Saturday night as "wrap around"
moisture moves over the area from a low pressure system in the
Gulf. However, precipitation amounts will be very light as
downsloping off the Alaska Range will significantly reduce
precipitation amounts and intensity. Snow shower probabilities are
much lower across the Kuskokwim Delta and western Bristol Bay.

&&

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

Unsettled weather continues across the Bering/Aleutians over the
next few days. Ocean-Effect snow showers are expected to continue
across the eastern Aleutians and western Alaska Peninsula through
Friday morning as strong cold air advection persists across the
eastern Bering Sea. A frontal boundary that is currently over the
central Bering/Aleutians will continue to produce small areas of
gale force winds through Friday morning before the front weakens
and conditions gradually ease. The strongest winds will be along
the south side of the Aleutian Chain due to the funneling
northwesterly winds between the gaps along the Aleutian Chain.
There is moderate confidence with respect to the position and
intensity of a low pressure system expected to move eastward
across the Aleutians this weekend.

&&

.Marine (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: Winds will diminish on Saturday through Sunday as
the low in the western Gulf weakens near Kodiak Island. Another
low approaching the Gulf from the west Sunday night through
Monday will increase winds along the front, potentially to 30 kts
with gusts to gale force, but the exact location of the front and
highest winds in the Gulf going into next week is low to
moderately uncertain. Seas less than 8 ft will build to the west,
south of Kodiak Island with the approaching low on Monday
morning.

Bering Sea: Northerly flow over the eastern Bering continues as a
low over the western Gulf continues to weaken on Saturday and
another low along and south of the Aleutian chain moves eastward
throughout the weekend. Rain and snow showers are expected near
the low. Winds near the Aleutians will approach the low end of
gale force. A South Kamchatka low is expected to move into the
western extent of the Aleutians Monday morning with the potential
for gale force winds and southerly flow through the western Bering
sea. Seas generally 8 feet or less throughout the weekend will
build up to approximately 20 feet over the western Bering.

&&

.Long Term Discussion (Days 4 through 7: Sunday through
Wednesday)...

A weakening low over the western Gulf near Kodiak Island will
gradually diminish precipitation beginning near the eastern
Aleutians and AKPen Sunday and continue to decrease chance near
Kodiak Island into Monday. As this low weakens, another low moving
eastward just south of the Aleutians will enter the Gulf and
keeping some chance of precipitation over the Southcentral Gulf
coast and Kenai Peninsula through at least Tuesday evening. Model
certainty decreases during this timeframe and the extent north and
eastward of the Gulf low will impact chances and thus the total
precipitation an area may expect. A brief break is possible over
Southcentral by midweek. Further west, a Kamchatka low will reach
the far western extent of the Aleutians by Monday morning pulling
warmer Pacific air into the Bering. As the low sweeps eastward
it may begin to track south of the central and eastern Aleutians
by midweek next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning: 119.
         Gale Warning: 120 125 130 131 138 139 150.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...VR