Gale Warning 818, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 PM AKST Sat Dec 10 2022

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified across the North Pacific. An upper
level trough currently extends across the Bering/Aleutians. Upper
level ridging extends across the Gulf with the ridge axis
extending over Southwest Alaska. The jetstream remains south of
50N west of 175W, then extends northeastward to over the northern
Gulf and Southwest Alaska. The jet then extends southeastward from
the Kenai Peninsula into the North Pacific.

Closer to the surface, radar and observations showing snow moving
eastward across Bristol Bay towards Cook Inlet and the Kenai
Peninsula.

&&

.MODEL DISCUSSION...

Guidance is showing more agreement with respect to the placement
and intensity of synoptic scale features. The biggest forecast
challenge continues to be fine tuning the precipitation and
snowfall accumulation forecast across Southcentral. Precipitation
type also remains a challenge in the immediate coastal areas.

&&

.AVIATION...
PANC...Conditions will remain VFR through 11th/10z. Vicinity fog
can potentially reduce visibility before 09z. Light snow will
reduce visibility and ceilings to MVFR between 11th/10z and
11th/14z. Conditions will then return to VFR after 11th/14z. Light
winds persist for this TAF package.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3;
This afternoon through Tuesday afternoon)...

Clear skies earlier today have given way to clouds for most of
Southcentral Alaska as the flat ridge overhead progresses off to
the east. Parts of the Copper River Basin still exhibit clear
conditions. As the ridge moves away, west-southwesterly to
eventually southwesterly flow aloft will become dominant over
Southcentral as the well advertised winter storm moves in from
the southwest. Parts of southern Kodiak Island are beginning to
see precipitation as a frontal system moves northeastward.
Precipitation is expected to being in Kodiak City as snow this
evening before changing to rain over night as warmer air pushes
in.

Snow reaches the Kenai Peninsula overnight and progresses
northward to Anchorage, Mat-Su Valleys, and Prince William Sound
communities through the day on Sunday. Cross-barrier/southeasterly
flow may limit snow initially for Anchorage and the Matanuska
Valley before intensity picks up Sunday Afternoon into the
overnight hours. Snow will taper off from west to east Monday
morning through the afternoon and evening. Eastern parts of the
Copper River Basin will still contend with light snow through
Monday night. Precipitation type appears to be mostly in the form
of Snow, even near the coastal locations. There is still a little
bit of uncertainty with the Cordova area as a barrier jet will be
near by and potentially introduce a little warmer air, providing
for mixed precipitation Monday morning before changing back to
snow Monday afternoon.

Confidence remains high for a significant and impactful winter
storm spanning generally from tonight, starting in the Kenai
Peninsula, and lasting through Monday night, ending for Eastern
parts of the Copper River Basin. With that, Winter Storm Warnings
have been issued for the Kenai Peninsula while Winter Storm
Watches remain out for Anchorage area, Mat-Su Valleys, and the
Copper River Basin. Please refer to these products for more
specific information.

After this system finally exits Monday night, the active weather
pattern continues with next weather-maker is on its heels for
Tuesday as more snow is possible area-wide. Please pay attention
to forecast updates as finer details continue to be nailed down
with respect to the system for tonight through Monday and as the
weather pattern evolves for Tuesday and beyond.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Tuesday)...

A deepening low will track towards the Alaska Peninsula this
evening and then move into the western Gulf. North of the
aforementioned low, a band of moderate snow will develop first
over Bristol Bay and then spread northeast into the Lower
Kuskokwim Valley tonight. This is anticipated to be a long
duration event, with steady snowfall not expected to end until the
low pushes into the northern Gulf Coast and as colder, drier air
filters in from the northwest late Sunday night into early
Monday. Storm total snowfall amounts for Bristol Bay are expected
to range from 6 to 12 inches, with the heaviest amounts focused
across the eastern half of of the region closer to the Alaska
Range. As such, a Winter Weather Advisory has been issued for the
Bristol Bay area for this evening through early Monday morning. A
second Winter Weather Advisory has also been issued for the Lower
Kuskokwim Valley starting 9PM AKST tonight through early Monday
morning with storm total snowfall accumulations ranging from 6 to
12 inches as well. By Monday, the return of clearer and colder
conditions will likely be cut short due to another low and its
associated front expected to reach the coast with another round
of precipitation by Monday evening. With the progressive nature
of the pattern, this will likely be quick shot of snow, with the
possibility of rain mixing in along the coast as the low
approaches the Y-K Delta early Tuesday morning.

&&

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

A low that is currently located over the Gulf of Anadyr and its
associated front continue to produce gusty westerly winds across
the northern Bering. Highest winds will mainly be across the
central and northern Bering near the Pribilofs and Saint Matthew
Island through tonight as the low continues to lift north. By
Sunday, a push of colder air wrapping around a surface low located
near the Alaska Peninsula, will help initiate snow showers across
the eastern Aleutians and Pribilofs, while also aiding in the
development of northwest gap winds. These winds will steadily
increase to gale force out of bays and passes along the southern
Alaska Peninsula and eastern Aleutians through Monday morning.
Meanwhile, another low will move into the southwestern Bering
between Sunday and Monday, which will usher in gale force winds
and rain across the western Aleutians. The low and its associated
front will track east through Monday night and will push gusty
winds and rain across the rest of the Aleutian Chain and Pribilofs
as it advances towards the Southwest coast through the week.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)...

Very active weather looks to continue throughout southern Alaska
and Bering Sea in the long term. The main features of concern are
a high amplitude trough over the Bering and north Pacific and a
Rex Block from British Columbia south to the West Coast. The main
uncertainty in the forecast is related to the interaction of the
storm developing over the north Pacific on the southern edge of
the trough axis and the blocking ridge as it moves east. With the
high amplitude trough/ridge pattern, ample warm air and an
atmospheric river are expected to move north into the southern
Mainland. Right now deterministic guidance has two main storm
tracks, one through the eastern Bering and into the Interior and
the other into Bristol Bay and the Gulf of Alaska. The east/west
position of the low will determine precipitation type midweek for
both Southcentral and Southwest. The ECMWF and Canadian solutions
show a more amplified solution with a low farther to the west
(eastern Bering and Interior Track), which would lead to rain
across the southern Mainland Wednesday and Thursday, with chances
for snow on the backside as the system occludes. The GFS solution
has a more easterly storm track, which would lead to heavy snow
over the Kuskokwim River areas, rain for Bristol Bay, and mixed
precipitation for Southcentral. The forecast is highly uncertain
and pertains in many ways to the north/south positioning of a low
moving across the southern Mainland on Tuesday, with the more
southern solution helping to keep temperatures aloft cooler and
visa versa. This storm will likely be very impactful, but the
question of how it will be impactful (rain vs snow) is to be
determined.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 121 125
         Winter Storm Watch 101 111 141 145
         Winter Weather Advisory 152 161
MARINE...Storm Warning 119.
         Gale Warning 120 125 130-132 138 139 150 155 160 165 173
         174 176 177 351 352
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...DAN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...CJ