Storm Surge in Alaska, December 3 to 4, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 AM AKST Sat Dec 3 2022

.ANALYSIS AND UPPER LEVELS...

Broad upper level ridging continue shifting eastward over the next
couple of days. Longwave upper level troughing exists out over the
Bering Sea, with a surface low reflected at the base of the
trough. The front extending off the low will push towards
Southwest Alaska by Sunday morning, moving eastward towards
Southcentral Alaska through Monday morning. A transient ridge
builds behind the system, that will bring a very brief bit of
reprieve between fronts. There is a low developing over the
Kamchatka Peninsula whose front moves into the western Bering Sea
Sunday afternoon. The front will move towards Southwest Alaska
through Monday night.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. There is better agreement for the elongated Bering low as it
tracks northwards. The surge of warm air with the front may bring
forecast challenges regarding precipitation type in Southwest
Alaska.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Saturday through Monday night)...

An upper-level ridge over the Gulf of Alaska will keep conditions
generally calm and dry through the weekend. Periodic mid and high
levels clouds will move across the region, however, as a series
of weak upper-level waves move around the top of the ridge. 850
mb temperatures with this ridge are hovering around 0C to 2C,
keeping a strong inversion in place, with valley locations
generally remaining in single digits and teens and temperatures
at higher elevations ranging from 28 to 40 degrees.

This ridge, while persistent, will begin to breakdown and slide
east by late Sunday. As it does, low stratus over the southwestern
Gulf of Alaska will begin to drift northward on a southerly wind
flow. These clouds will move over Kodiak Island later today, and,
perhaps, move as for north as the immediate Southcentral coast by
Sunday morning.

As the ridge departs, a front will move over Cook Inlet from the
west. Light snow is expected to overspread the Kenai Peninsula
north to the Mat-Su Valleys by Monday afternoon, slowly moving
west by Tuesday morning. Temperatures are expected to warm due to
the southwesterly wind flow ahead of the front. The warmer
temperatures may make for a rain/snow mix along the coast,
especially around Homer and Seward, before colder air returns
behind the front and changes any residual precipitation back to
snow. This system will weaken as it runs into the ridge, meaning
that snowfall is expected to be light, with a general 1 to 3
inches of snow possible from Kenai north to Palmer and Talkeetna.

&&.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today and
Sunday)...

A ridge of high pressure remains anchored over the region,
providing benign conditions and an influx of clouds moving
overhead. For today, a couple of weak shortwaves riding on top of
the ridge may provide enough lift for rain in Toksook Bay, and
upslope precipitation in Bristol Bay. For the rest of the weekend,
the ridge axis shifts slowly eastward in response to a deepening
trough setting up over the Bering Sea. The main weather feature
with this trough is associated with a North Pacific low lifting
north of the western Aleutians Islands. Along and ahead of the
low is a front that will reach the eastern Bering Sea by Sunday
morning. This will bring a round of precipitation for the Alaska
Peninsula and across the western mainland between Sunday and
Monday. Increasing southerly winds will accompany the front and
help draw enough warmer air for rain as the main precipitation
type for the low-lying areas.

There are some timing differences, however, on how quickly the
front pushes eastward. In the wake of the front, colder air
filters across Bristol Bay sometime late Sunday night and early
Monday morning. As the atmospheric column of air cools above the
surface, this will allow rain to transition to either a wintry
mix or a brief period of snow. Any snow accumulations will
generally be light, with less than 2 inches expected. A brief
break of drier weather is in store for the rest of Monday as a
transient ridge builds overhead before the next round of
precipitation returns Monday afternoon/evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2:
Today and Sunday)...

A broad upper trough over eastern Russia extends southward into
the Bering Sea. Ahead of the trough, a low pressure system is
lifting north of Amchitka, bringing unsettled conditions as the
main front pushes eastward. Rain will increase in coverage
throughout the today, with widespread gales along the Aleutian
Chain and over the Pribilof Islands. The low will then track near
Saint Paul Island by Sunday morning, with southerly gales out of
the bays and passes for the eastern Aleutians. As the
aforementioned upper trough lifts northward into the Bering
Strait, rain is expected to taper off along with subsiding winds
by late Sunday night. A rinse and repeat is in store on Monday as
another low over eastern Russia pushes a gale force front across
the western Bering Sea and along the Aleutian Chain.

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

Active weather is in store for Southern Alaska and the
Bering/Aleutians next week as multiple systems parade across the
regions. On Tuesday, a longwave upper-level trough encompasses
the entire Bering Sea/Aleutians while a ridge sits over the
Mainland. As the trough amplifies across the Alaska Peninsula and
Southwest Alaska on Tuesday and Wednesday, it shunts the upper
ridge east into Canada. An associated surface front will weaken
over Southwest on Tuesday morning while a surface low develops
near the Alaska Peninsula that same morning. Model agreement with
this low begins to diverge on Wednesday, but there is general
consensus for the feature to track across the Gulf and to the
Panhandle by late Thursday. Overall, there is decent confidence
that Southern Alaska can expect cooler temperatures and
precipitation (likely snow) on Tuesday and Wednesday before an
upper-level ridge builds over the region, tapering off
precipitation for Thursday and Friday.

Out west, model agreement still worsens by Wednesday in regards
to the track and strength of a North Pacific low. The
deterministic GFS supports the low tracking into the southcentral
Bering Sea by Thursday morning and then east to the Alaska
Peninsula by Friday morning. On the other hand, the deterministic
ECMWF keeps the low south of the Aleutians and tracks it due east
to the Panhandle by Friday morning. Lastly, the deterministic
Canadian model tracks the low north across the Bering and towards
Russia by Friday morning. The Canadian model currently depicts the
strongest low in terms of central pressure and wind strength.
Overall active weather is expected for the Bering and Aleutians in
the longterm despite the remaining forecast uncertainties.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 150 155 160 165 170-181 185 411-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
LONG TERM...AF