Gale Warning 805, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Mon Dec 11 2023

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

A winter storm remains in progress across much of southcentral
Alaska. Latest satellite imagery shows the deep, broad cyclone
gradually shifting eastward across southern Alaska. The attendant
warm front with this cyclone is currently lifting through the
Chugach Range, with the cold/occluded front extending southward
through the Kenai Peninsula. The atmospheric river behind the warm
front of this system has brought a fetch of very warm, moist air
from the North Pacific into the Central Chugach eastward. A winter
storm warning remains in effect for this area, specifically
Thompson Pass and the adjacent area where 2-3 feet of snow is
likely be the time this system wraps up on Tuesday.

Elsewhere, PAHG and PAIH radars show (mostly) snowfall moving
northward across the Kenai Peninsula into Anchorage and the Mat-Su
Valley. A rather strong downslope shadow on the west side of the
Kenai and Chugach mtns has kept precipitation limited overnight,
but latest radar trends show that the this precip shadow is now
diminishing as cross-barrier flow subsides. Snowfall in the
vicinity of 1-2 inches is possible for the Kenai northward into
Anchorage and the Matanuska Valley today, with locally higher
amounts. Heavier snow is expected for the Susitna Valley, where
another 6 to 10 inches is possible from Talkeetna north.

For tonight night and beyond, much of the forecast remains highly
in flux. Models continue to mostly trended towards a more east
solution for the next low expected to lift northwest into the Gulf
around the nearly stalled upper trough centered over the Alaska
Peninsula, and this low should reach the coastline by Tuesday
morning as it follows along a wavering frontal zone stretching
over the Gulf. A near continuous stream of moisture firing into
the mainly eastern sections of the Gulf coastline will result in
near continuous snow (low-level coastal rain) for mountainous
areas, with blizzard conditions possible in susceptible areas such
as Thompson Pass. A big forecasting challenge with this next
system will be the degree of 'inland' (including much of the
Copper Basin) precipitation and the amount of warm air trying to
filter into valleys that could cause some mixing with rain between
Monday and Tuesday, including near McCarthy and Chitina. Farther
west out towards the Kenai Peninsula and Mat-Su Valleys, the
potential for additional snowfall past Monday morning has down-
trended, with the majority of scenarios (now reflected in this
forecast package) are keeping this region mostly dry through
Tuesday night.

Yet another low pressure will join the parade of systems arcing
north and west from the North Pacific on Wednesday morning. While
details are again not clear-cut, it looks like there will be
better chances this time around for light snow to spread back over
to eastern parts of the outlook area, while another batch of
moderate snow (and again possible mixing with rain near the coast)
moves into the Prince William Sound and Copper River Basin. Stay
tuned for the forecast and for more updates to come as this very
active winter pattern continues.

-Brown/AS

&&

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

An amplified pattern continues over the Bering and Southwest
Alaska this morning with a deep upper low situated over the Alaska
Peninsula. An upper level front is pushing into the Western
Aleutians with downstream ridging immediately west of the Central
Aleutians. Northerly flow ahead of the ridge and on the backside
of the AKPEN low is allowing cooler air (sub 32 degrees) to spill
southward, uninhibited. Water vapor imagery reveals just how far
south the colder air mass has traveled. Convective showers from
the cooler air moving atop warmer sea surface temperatures extend
as far south as 40N and along 170W. Cooler temperatures will
continue to filter southward, including Southwest Alaska, over the
next few days.

Short term updates include the tail-end of a blizzard warning
over Bristol Bay and a Winter Weather Advisory over the Lower
Kuskokwim Valley. While the upper low over the Alaska Peninsula
will continue to promote periods of snow through the afternoon and
evening hours, winds are already steadily decreasing. This will
see any threat for blizzard conditions come to an end. Even
without the wind threat, morning visibilities range from a 1/2
mile to 1 1/4 miles across Dillingham, New Stuyahok, and Koliganek
as snow continues to fall.

This bring attention back to the temperature forecast. Overnight
lows across the Kuskokwim Delta dropped to briefly below zero last
night. Bethel reached -3 degrees before warming to 2 degrees. The
daytime hours will promote little warming, if any, before
nighttime befalls the region and sees temperatures once again dip
below zero. Northerly winds gusting to around 25 mph will see wind
chills range from -25 to -28 degrees during the morning hours on
Tuesday and again on Wednesday. Precipitation largely comes to an
end across Southwest by late Tuesday into Wednesday.

Finally, a Kamchatka low is expected to bring the next frontal
system into the Western and Central Aleutians by midweek. This
will bring a wedge of warmer and above freezing temperatures
across the Aleutians, along with a changeover from snow back to
rain.

BL

&&

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

The long-term forecast remains on track for the continued
unsettled and active pattern for Southern Alaska, the Bering Sea,
and the Gulf of Alaska. For Thursday and Friday, an upper level
low in the Gulf opens up into trough as it progresses eastward to
Southeast Alaska. Any snow showers should be confined to the
coastal mountains through Friday. Another deep trough moves
eastward to the central Bering Sea and becomes stationary by
Sunday. A gale to storm-force low pushes its front eastward from
the Central Aleutians to the coast of Southwest Alaska through
Friday. There will be a warm push of air with this front. Thus,
while precipitation could start as snow ahead of the front,
precipitation will quickly change to rain as the warm air works
in. Precipitation type is a little more uncertain for Southwest
Alaska Friday due to timing differences in when the parent low in
the western Bering occludes as well as when a secondary low forms
along the front. Regardless, precipitation overspreads Southwest
during the second half of Friday and makes it into Southcentral
Friday evening and Saturday. Coastal locations of Southcentral
look to again see the most precipitation with more uncertainty
for inland locations due to downslope drying flow. Cold air
continues to spill into the Bering Sea Saturday and Sunday as the
occluded low remains in the Bering with snow showers a good bet
for Aleutian Chain. Sunday for Southcentral features a lot of
uncertainty with regard to the track of a potential Gulf low.

&&

.AVIATION...

PANC...Gusty northerly winds over the terminal will persist into
the early morning hours before shifting southerly by 15Z. Snow
moving over the terminal will similarly persist into the early
morning hours Monday, with areas of loose snow blowing around
possible. The chance for snow will be low Monday with some showers
pushing up and over the mountains possible, however diminishing
throughout the day. Showers will then persist in the vicinity
through the day Monday. Most likely ceiling/vis will bounce up and
down as snow showers move over the terminal. There is a small
chance of low level wind shear sometime between 09Z and 12Z as
easterly flow strengthens along Turnagain Arm and the front range
Chugach.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
945 AM AKST Mon Dec 11 2023

AKZ155-121500-
Kuskokwim Delta-
Including the cities of Bethel and Nunivak Island
945 AM AKST Mon Dec 11 2023

...BLOWING AND DRIFTING SNOW ALONG THE KUSKOKWIM DELTA COAST
THROUGH WEDNESDAY...

Gusty northerly winds will persist across the Kuskokwim Delta
through Wednesday. Wind gusts as high as 45 mph are forecast to
continue along the Kuskokwim Delta coast and for Nunivak Island.
No new snowfall is anticipated from Bethel west to the Kuskokwim
Delta coast, though strong winds will continue to loft
transportable snow already on the ground. As a result, visibility
will be reduced at times, though will generally remain above one
mile. Winds diminish on Wednesday, ending the threat of blowing
and drifting snow.

AKZ181-121500-
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
945 AM AKST Mon Dec 11 2023

...BLOWING SNOW ALONG THE ALASKA PENINSULA THROUGH WEDNESDAY...

Northerly winds gusting to 45 mph are currently combining with
persistent snow showers to reduce visibility to one quarter mile
at times. This evening, snow showers should decrease in intensity,
allowing visibility to improve somewhat. However, intermittent
reductions in visibility to one half mile will remain possible.
Wind gusts are forecast to increase to 60 mph Tuesday night, which
may lead to prolonged periods of low visibility. Winds diminish
on Wednesday, ending the threat of low visibility due to blowing
snow.

Preliminary Local Storm Report
National Weather Service Anchorage AK
1024 AM AKST Mon Dec 11 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0730 AM     Snow             Valdez                  61.14N 146.37W
12/11/2023  M10.0 inch       Chugach            AK   Public

            A member of the public measured 10 inches of
            snow. Snow transitioned to rain around 7:30
            am.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
103 PM AKST Mon Dec 11 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 AM     Snow             Trapper Creek           62.32N 150.24W
12/11/2023  M10.5 inch       Matanuska-Susitna  AK   Public

            5.9 inches overnight with another 4.6 by
            noon.

&&