Gale Warning 177, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Mon Feb 12 2024

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

High pressure in the Gulf of Alaska will continue to build as it
moves northward reaching Yakutat tomorrow evening. This will
result in continued southerly to southeasterly wind flow into
Southcentral Alaska. Wind gusts in the Anchorage Hill sides and
Turnagain Arm will range from 60 mph to 80 mph through tomorrow
morning. Elsewhere in the Anchorage area and Mat-Su Valley, wind
gusts in this range will be less frequent but continue the upward
trend of today's 30 and 40 mph gusts to 45 and 55 mph gusts into
the overnight hours. Unseasonably warm temperatures can be
expected through Wednesday.

The Gulf of Alaska high pressure will keep a frontal boundary
over Kodiak Island through mid-week allowing for a continuous
stream of moisture to flow over Kodiak Island during this time.
Short term rainfall amounts in the city of Kodiak range from 1 to
2 inches but just west of the city, rainfall amounts will range
from 2 to 5 inches from today through Wednesday. A brief lull in
this first round of rain is expected Wednesday afternoon,
however, the threat of rain in Kodiak Island is expected to
continue through late this week.

&&

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

A Pacific low crosses into Bristol Bay Monday night. Strong winds
and temperatures in the mid to upper 30s for the northern Alaska
Peninsula, Bristol Bay, and Lower Kuskokwim Valley through
Tuesday.

While the low weakens, it is followed by an atmospheric river
inbound to the Bristol Bay forecast zone. A stark east-west
temperature gradient aloft separates the difference between rain
and snow. Forecast sounding temperatures support mixed
precipitation through Tuesday afternoon, after which transition to
all snow will occur. Given abundant available moisture, higher
elevations and inland areas could receive 12+ inches of heavy snow
through Wednesday. Southerly winds and slightly warmer
temperatures will lower snow totals for coastal communities.

This long duration precipitation event for the Alaska Peninsula
and southern Bristol Bay continues through Wednesday. Water
equivalent precipitation amounts of 0.75 to 2.5 inches are
possible.

&&

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

The long term begins with a stagnant upper-level ridge / trough
pattern east to west across the state. A 560dm ridge anchored over
the St. Elias Mountains Wednesday drifts northeast over the Yukon
for Friday before weakening and elongating as it continues a slow
push to the southeast over British Columbia. The broad trough over
the Bering and Aleutians also remains in place through the end of
the week. The result is a general west to southwesterly flow in
the mid levels across the southern Bering and Aleutians shifting
to a southerly flow from the western Gulf and Alaska Peninsula
north along the west coast of Alaska. Various shortwaves embedded
in the flow, along with a strong upper-level jet, are resulting in
a seemingly continuous parade of surface lows and troughs moving
from the North Pacific toward the Alaska Peninsula and Kodiak,
eventually moving farther north to the Bering Strait.

This storm track favors periods of heavy precipitation, in the
form of low elevation rain and mountain snow, from Kodiak Island
to the Alaska Peninsula and along the south-facing hills and
mountains of Southwest Alaska, due to upsloping. With multiple
surface lows tracking north across the Alaska Peninsula, strong
southeasterly gap winds and mountaintop winds are also likely,
with the strongest of the gap winds across the Alaska Peninsula
and through Kamishak Gap into the interior Bristol Bay region.
The southeasterly flow will also promote periods of showers
across the Kenai Mountains along with strong southeasterly gap
winds, mainly through Turnagain Arm and across the Matanuska
Valley.

The greatest uncertainty comes closer to the weekend, as models
try to weaken the ridge at differing times with the weaker, more
easterly positioned ridge and upstream trough becoming more
negatively tilted. This scenario would likely allow for storm
systems to move farther north into the Gulf of Alaska with
steadier precipitation moving toward the Southcentral coast.

Confidence is increasing that a strong low will bring gale- and
storm-force winds to the western and central Aleutians Friday into
Saturday, along with heavy rain and snow along the attendant
front.

&&

.AVIATION...

PANC...VFR conditions will generally prevail for ANC through the
TAF period. LLWS remains the biggest concern with strong SE winds
not too far above the surface. The 00Z AFC sounding sampled
approximately 30kts at 2kft. This is likely to strengthen to
closer to 45kt through the evening and overnight before
diminishing later on Tuesday. The resultant downsloping dry air
should keep precipitation out of Anchorage, though can't
completely rule out a few rain drops. Wind will generally remain
out of the SE with the potential for strong gusts upwards of 30kt
out of the Turnagain Arm.

-Brown

&&