Gale Warning 10, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
418 PM AKST Tue Jan 9 2024

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

Relatively quiet weather is underway across southcentral Alaska.
GOES water vapor imagery shows an upper-level ridge axis beginning
to shift east into western Alaska. Meanwhile, an area of low
pressure in the SE Gulf of Alaska continues to trek southeastward.
The pressure differential between the building ridge and departing
low has resulted in gusty 20-30kt winds out of all the favored
outflow gap locations along of the Gulf coast.

Mid/upper-level clouds will continue to clear out across
southcentral Alaska this evening. Fog development is expected once
again, but with considerable uncertainty with regards to the extent.
The highest probability of fog development is across the Cook Inlet,
including Knik and Turnagain Arms, and adjacent land areas along the
Kenai Peninsula and Anchorage. Higher uncertainty exists across the
Susitna Valley and the Copper River Basin, where model forecast
soundings suggest low-level air may remain unsaturated and
slightly more mixed than it otherwise would be given some light
low-level wind.

Wednesday will be quite similar to today as far as the weather is
concerned across southcentral Alaska. Anomalously strong, cold
high pressure will slide southward across Yukon, just clipping
eastern Alaska. While much of Alaska will have steady temperatures
or begin seeing a warming trend, eastern Alaska including the
Copper River Basin, will see temps fall... with a solid period of
72 hours or more of below 0 temps for that area. Elsewhere, much
of southcentral Alaska should see another day with mostly clear
skies should morning fog / low stratus clear out. Upper-level
cloud cover will begin to thicken late tomorrow in response to the
approach of the next system.

Models are in fairly good agreement with the next trough and
associated low pressure system bringing rain (and high-elevation
snow) to Kodiak Island by Thursday and continuing through Friday as
the effective warm front with this trough butts up against cold air
spillover from the Yukon / SE Alaska cold high pressure. This will
keep the precip and strong SE flow focused across Kodiak Island, as
well as the Barren Islands. Model guidance has been suggesting
widespread precip amounts of 1.5 to 3.5 inches for this area,
including Kodiak City, by Saturday morning.

With the aforementioned cold air spilling in from the east, models
are hinting at the possibility of showery convection across the
Gulf of Alaska Thursday into Friday as well. Upper-level lift is
lacking, but forecast soundings across the Gulf suggest 0-850mb
lapse rates on the order of 8 C/km. With this setup, think some
snow showers may push into the Prince William Sound and into the
northeast Kenai Peninsula... but most activity should remain off
and east of the road network.

-Brown

&&

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

The forecast is largely on track with the progression of an
occluded upper low just now approaching the Western Aleutians from
the south this evening. The most notable change with the latest
forecast package is that the front's arrival to the Kuskokwim
Delta Coast has slowed. As such, the start time of a Blizzard
Warning for Nunivak Island and the Kuskokwim Delta Coast has
shifted from midnight tonight to 3AM AKST, and the end time has
been pushed back from noon on Wednesday to 6pm AKST. MOS guidance
has been hinting at a longer duration of reduced visibility due to
blowing snow with enhanced east to southeast winds persisting
throughout the day on Wednesday. An eventual transition to rain is
forecast for locations south of Toksook Bay, which should see the
threat of blowing snow come to an end earlier. It's becoming
increasingly likely that Mekoryuk and Toksook Bay never transition
to rain. As a result both locations are expected to see the
higher snow accumulations of up to 8 inches or more. The
changeover to rain will see a period of freezing rain from Bethel
down to as far as Kipnuk, but the short duration of freezing rain
should preclude ice accumulations as temperatures continue to
warm.

As the upper low moves across the Central Aleutians, widespread
gusty conditions remain forecast across the Bering as well as the
Aleutians and Alaska Peninsula. Gales with higher gusts will be
common. By tomorrow evening, south to southeast winds will stretch
from the Alaska Peninsula, across Bristol Bay, and through the
Etolin Strait, as the axis of stronger winds shifts eastward. As
we move into Thursday the axis will result in southeast winds of
30 to 50 mph across Greater Bristol Bay, with the strongest winds
to spill out of the Kamishak Gap.

Looking at current observations, winds are gusting to over 40 mph
across the Pribilof Islands. Snow and blowing snow has brought
visibility down to 3/4 miles. This should slowly improve through
the evening hours with temperatures to gradually warm to above
freezing over the next few hours thanks to strong southerly flow
behind the lifting Bering Sea front. The extension of the front is
currently draped over the Alaska Peninsula. Widespread snow
showers are ongoing from Nelson Lagoon, south. Sand Point is
currently down to 1 mile of visibility with temperatures at 34
degrees. Snow will steadily lift northward and expand into the
rest of the Alaska Peninsula through the evening hours, also
eventually transitioning to rain as temperatures finally warm.

As was mentioned in previous discussion, the next upper low is
forecast to push across the Aleutian Chain beginning late
Thursday/Thursday night. This next low will be somewhat weaker
than its predecessors and is also expected to take a more easterly
track, as opposed to the northerly tracks through the Central
Bering.

-BL

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

A north Pacific low crosses the Alaska Peninsula into Bristol Bay
Friday afternoon. This system pulls a long stream of
precipitation from the north Pacific into Southwest Alaska.
Several bands of snow sweep across Southcentral Saturday and
Sunday. Precipitation clears out Sunday afternoon through Monday
afternoon before a north Pacific low moving westward, from south
of the Gulf of Alaska, projects its front to the northern Gulf
and across the AKPen.

&&

.AVIATION...

PANC...The primary forecast challenge is fog and low stratus.
The environment is ideal for fog formation, with a low level
temperature inversion already in place and a high amplitude ridge
building in from the west tonight through Wednesday. Thus, there
is high confidence in development of fog with LIFR ceiling/vis,
but much lower confidence on when it will impact the terminal.
Ceilings and visibility will rapidly fluctuate from VFR to LIFR
this evening as the fog moves in and out of the area. Conditions
will settle on LIFR conditions later this evening with the 12Z to
18Z time period being the most favored time for the lowest
conditions. Fog will then likely linger in the vicinity through
the day Wednesday and perhaps even through Wednesday night.

&&