Small Craft Advisory 229, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKDT Tue Mar 15 2022

.ANALYSIS AND UPPER LEVELS...

A deep and cold upper level low and trough are digging southward
across western Alaska and the eastern Bering Sea, leading to
moderate to strong cold air advection. This is leading to gusty
northerly winds along the southwest Alaska coast, Pribilof
Islands, and on south to the southern Alaska Peninsula and eastern
Aleutians. Widespread stratocumulus clouds have formed over the
Bering Sea as the cold air moves overtop of relatively warmer
water. These clouds are tracking south to the Aleutian chain and
Alaska Peninsula. There are also some snow showers embedded within
this cloud deck, especially along the corridor of strongest cold
air advection.

Much of southern Alaska was clear and cold this morning. However,
clouds are increasing as the upper low over western Alaska digs
southward and low level southerly flow strengthens over Southcentral.
This is leading to upslope flow and clouds focused along the
south side of area mountains. Meanwhile, a vertically stacked low
south of the Alaska Peninsula is moving slowly eastward, while
deep southerly flow is forcing the associated occluded front
northward into the Gulf of Alaska. Precipitation is overspreading
Kodiak Island this afternoon, mainly in the form of snow.

&&

.MODEL DISCUSSION...

Models are in relatively good agreement with handling of large
scale features over the next few days. There are some minor
differences in position of the upper low center as it settles
south of the Alaska Peninsula/Kodiak Island on Thursday. More
importantly, a trough rotating around this upper center will
interact with a short-wave and developing surface low crossing
the North Pacific on Thursday, forcing the storm northward into
the Gulf of Alaska. Solutions vary a little more with track of
this storm system, so the forecast will have to be adjusted with
time. However, there is good agreement in overall strength, with
gale force winds likely across the Gulf waters.

&&

.AVIATION...

PANC...VFR conditions will persist. A weak upper level short-wave
will move up from the Gulf between about 06Z and 09Z, bringing a
good chance of snow. Overall forcing is weak, low level flow will
be in the process of shifting from south to southeast (with some
blocking/downsloping), and northerly surface flow will tend to
hold in dry air. As a result, have backed off of snow in the TAF,
thinking this will likely be a quick dusting and ceiling/vis will
remain relatively high.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3:
Tonight through Friday)...

A weakening front will move up into the north Gulf Coast tonight,
sending snow across the Prince William Sound, Cook Inlet and Kenai
Peninsula regions from south to north. Farther south, a low will
develop along the front and focus an area of rain- snow mix across
Kodiak Island through tomorrow morning. It's looking even less
likely for the Mat-Su Valleys and the Anchorage area to see much
snow out of this system, with initially dry low levels, weak
forcing and increasingly easterly (cross-barrier) flow limiting
chances for much more than a dusting to half inch to reach the
ground before everything dries out tomorrow. In contrast, most of
the Prince William Sound and western Kenai Peninsula should see
steady snowfall begin this evening as onshore and upslope flow
increase, with several inches of new snowfall possible through
tomorrow afternoon. Some mixing with or a changeover to rain is
expected near sea level by tomorrow afternoon as temperatures warm
above freezing and snow level rise, including near Portage,
Whittier and Seward.

From Wednesday night into Thursday, a deep upper level low will
drift slowly southeast over the Alaska Peninsula, keeping steady
light precipitation focused mainly near the coast with continued
moist, southeast flow off of the Gulf. Modified Arctic air may
actually wrap around the low and enter the western Gulf from the
southwest, changing lingering areas of rain and snow over to all
snow as the air mass progresses across Kodiak Island and
eventually up into the Kenai Peninsula later on Thursday. Another
North Pacific low is expected to enter the southern Gulf by
Friday, with some uncertainty remaining for how this low will
interact with the existing upper center moving south of Kodiak by
this point. Still, it looks likely most of interior Southcentral
will stay dry, with stronger winds and precipitation with the low
and its attendant front again mostly limited to coastal areas and
out over open water.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This
afternoon through Friday)...

A cold and dry polar low will move south across the Kuskokwim
Delta tonight and then slowly move near Bristol Bay and across
the AKPen by Thursday morning this will bring stronger winds
across the area especially across the Kuskokwim Delta. Winds and
cold temperatures will create wind chills approaching -30 at
times. A low pressure system moving near Kodiak Island on
Wednesday will increase moisture across Bristol Bay with light
snow likely. Expect 1 to 3 inches of snow in most populated areas
from Iliamna to Dillingham as well as King Salmon. Areas of light
snow will continue through Thursday but will diminish through the
day. Winds will also diminish by Thursday afternoon as the
pressure gradient relaxes. On Friday an upper level low
originating in Siberia will bring increasing winds for the
Kuskokwim Delta and chances of snow showers across the area and
will reinforce the cold air.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: This
afternoon through Friday)...

Low level northerly flow will increase through Wednesday across
the eastern Bering as cold air from the Arctic moves south
through Thursday. This will create gales with storm force gusts
south of the eastern Aleutians and AKPen especially through bays
and passes. Another upper level low will move out of Siberia and
southward across the Bering Thursday and Friday this will bring
another shot of colder air and gale force winds across much of
the Bering, with continued gales with storm force gusts likely
south of the eastern Aleutians and AKPen on Friday. Otherwise
expect widespread snow showers across much of the Bering and
Aleutians as cold air continues through Friday.

&&

.Marine (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska: A well developed low and its front moves across
the Gulf through Sunday. Forecast models in good agreement.
Widespread high end gales around the low moving across the Gulf
and through the Barren Island and Kamishak Bay, diminishing
Sunday. Seas building to 18 feet for Saturday, subsiding Sunday.
Some freezing spray is expected South and West of Kodiak Island
for Saturday.

Bering Sea: Arctic high pressure moves across the Western Bering
abutting low pressure over Interior Alaska through Sunday.
Forecast models in good agreement. Gusty Northerly winds over the
Central and Eastern Bering increases to widespread high end gales
and extending across the Aleutians and Alaska Peninsula Saturday
through Sunday. Seas building to 18 feet along the Bering side of
the Aleutians and Alaska Peninsula for Sunday. Heavy freezing
spray expected over Central and Eastern Aleutian open waters. A
strong central North Pacific low brings gusty Southeasterly winds
to the Western and Central Aleutians Friday and Saturday. Seas
building to 20 feet along the Pacific side of the Aleutians
through Sunday.

&&

.Long Term Discussion (Days 4 through 7: Saturday through Tuesday)...

The latest operational model runs are in fair agreement with the
evolution and progression of the synoptic scale features, but
diverge in the specific details towards the end of the period. The
main synoptic features on Saturday will be an upper level low in
the central Gulf, while another low moves south of the Eastern
Aleutian Islands. Even though there is uncertainty regarding the
interaction of these two features, the GFS/EC/CAN and ensemble
means form a broad longwave trough extending from the North
Pacific to the Gulf of Alaska.

From Sunday and beyond, there is considerable spread with the
next system moving towards the Bering Sea. The GFS seems to be the
outlier in cutting off a deep low south of the Aleutians, while
the EC/CAN keep the main low well to the north. Nonetheless, there
seems to be a general consensus that a southerly flow pattern
will push a series of shortwaves and associated surface lows
northward. Confidence is moderate that precipitation will be
concentrated through the Panhandle and up into the southern
coasts. Much of the mainland should be relatively dry during the
period, with the exception for potential snow showers by this
upcoming weekend in the eastern interior. Otherwise, temperatures
are expected to be below normal across the coastal areas and
interior valleys as a general troughing pattern stays firmly
anchored over the entire Alaska mainland.

Out west, a ridge of high pressure will build across the Bering
Sea. A reinforcement of cold air advection will help drive
northerly winds funneling through the gaps and passes of the
Alaska Peninsula and Eastern Aleutian Islands. Wrap around
moisture on the backside of the aforementioned upper low will
bring occasional snow showers into these regions later this week.
A drying trend commences on Monday as the ridge axis shifts over
the western mainland, while a gale force front extending from a
Kamchatka low moves slowly east across the Western/Central
Aleutians.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119 130 139 150 155 172 180.
         Heavy Freezing Spray Warning: 140 150 155 160 165 179
                                       180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...KZ/MF