Gale Warning 763, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 PM AKST Thu Dec 1 2022

.ANALYSIS AND UPPER LEVELS...

Across the Bering and Aleutians a ridge is over the region causing
light winds and areas of fog and low clouds. Satellite and
observations also show fog and stratus clouds across the
Kuskokwim Delta. Satellite is also indicating an atmospheric river
south of the western and central Aleutians. Otherwise from
Bristol Bay through Southcentral mostly clear conditions are seen
with a few high clouds spilling over the ridge to the west.
Northerly flow is dominating Southcentral Alaska which is
producing gap winds with 40 to 50 knot gusts seen over the past
few hours for Kodiak City, Seward, Whittier, and the Valdez area.
Temperatures range from the teens and 20s across Southwest Alaska,
while 30s are common across the AKPen and 40s across the
Aleutians. To the east temperatures range from the 30s near the
coast to teens inland, with a few spots below zero this morning
across the Susitna valley.

&&

.MODEL DISCUSSION...

Models are in good agreement through Friday, however there model
differences on the progression of a low pressure system and front
moving into the Bering on Saturday and Sunday. These differences
with this system will cause precipitation timing issues as well as
precipitation type challenges across Southwest Alaska for Friday
through Sunday.

&&

.AVIATION...

PANC...VFR conditions are expected, however fog and low clouds
(IFR or below) are possible near the terminal after midnight
through the morning hours on Friday. Light northerly winds will
persist today and become variable tonight and tomorrow.

&&

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

Latest water vapor imagery depicts the synoptic pattern quite
well this evening. Yesterday's trough of low pressure has pushed
well into the Gulf of Alaska and is now tracking southeastward
along the coast of British Columbia. An amplified ridge of high
pressure over the Bering is now encroaching upon Southwest Alaska
and is expected to overspread Southcentral through tomorrow.
Between these two features the pressure gradient remains tightened
with enhanced northerly flow promoting elevated outflow winds
from Seward into Prince William Sound and the Copper River Delta.
As high pressure continues to move atop Southcentral, winds will
gradually diminish through Friday morning. This should promote
milder temperatures across Southcentral with highs in the 20's and
30's for all but parts the Copper River Basin and portions of the
Susitna Valley through the weekend. The only other concern over
the next few days will include potential fog development while
Southcentral remains beneath a high pressure inversion.

&&

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

A ridge of high pressure continues to track into the region
leading to clearer skies and dry conditions through Friday. On
the back side of the ridge, shortwaves will propagate on the
peripheral edge and track into the Kuskokwim Delta Friday night
into Saturday. The main concern is the potential for freezing rain
to accompany any precipitation associated with the shortwaves.
However, any precipitation and accumulation of freezing rain would
be trace amounts at most. The next feature of interest will
impact the region Saturday evening into Sunday due to a North
Pacific low tracking across the Bering through the weekend and
into Southwest. Freezing rain is the main concern for this next
system as well, but for mainly inland areas. Models have been
struggling to resolve the exact timing, placement, and intensity
of the aforementioned low, so be sure to check back in with the
forecast for updates as models get a better handle on this
feature!

&&

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

High pressure encompassing the Bering continues to shift eastward
through Friday night resulting in an unsettled, but benign
weather pattern. By Saturday, model disagreement rises on the
placement and intensity of a low that will track into the western
Bering and move eastward across the Bering. However, models have
come to a consensus of widespread gale force winds accompanying
the low as it tracks into Southwest Alaska. Be sure to check back
in with the forecast for updates as models come into better
agreement on this feature!

&&

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

An active pattern continues as several systems transit the Bering
Sea. Wet and windy conditions are in store through Tuesday, with
a transition towards cooler temperatures. Average model agreement
early in the extended period deteriorates significantly by
Wednesday, leading to significant uncertainty in the track of an
incoming North Pacific low.

The long-term forecast begins on Monday with two fronts, a weak
one extending over Mainland Alaska and a much stronger one
extending across the Western Bering and Aleutians. The first front
will continue to weaken as it tracks east through early Tuesday,
with precipitation likely to be heavy at times along the Alaska
Peninsula, Kodiak Island, and the north Gulf coast. The front over
the Western Bering and Aleutians will also weaken as it tracks
east. Heavy rain and winds up to storm force should weaken to
light precipitation and winds up to small craft speeds as the
front impacts Southwest Alaska Tuesday morning. As this second
front follows quickly on the heels of the first, there looks to be
an extended period of light to moderate precipitation (likely
snow, given cooler temperatures aloft) for Southern Alaska from
Monday through Wednesday. The biggest areas of uncertainty with
these fronts will be peak winds and the timing of incoming
inclement weather.

Model agreement deteriorates significantly by Wednesday.
Ensembles seem to support a North Pacific low moving up into the
Bering Sea on Wednesday, then dipping south into the Western Gulf
towards the tail end of Thursday. Deterministic models are in poor
agreement with the speed and strength of this low. The
deterministic ECMWF model cleaves most closely to the ensembles
but features a strong low with central pressure below 960 mb. The
GFS is much more conservative, with minimum pressure dropping to
the high 980s. Meanwhile, the deterministic Canadian model is an
outlier in that it keeps the low in the North Pacific. Much
uncertainty remains, though it looks highly likely that the Bering
Sea region and Southwest Alaska will see active weather at some
point on Wednesday and Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory: 145.
         High Wind Warning: 131.
MARINE...Gale Warning: 127.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...KC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
952 PM AKST THU DEC 1 2022

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

0932 PM     SNOW             4 NW WASILLA            61.63N 149.49W
11/30/2022  M3.5 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

0610 AM     SNOW             5 E ANCHORAGE           61.19N 149.76W
12/01/2022  M1.5 INCH        ANCHORAGE          AK   PUBLIC

0835 AM     SNOW             11 SE ANCHORAGE         61.07N 149.77W
12/01/2022  M2.0 INCH        ANCHORAGE          AK   PUBLIC

0919 AM     SNOW             2 E BUTTE               61.53N 149.01W
12/01/2022  M3.7 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

0415 PM     SNOW             12 SSE ANCHORAGE        61.06N 149.76W
12/01/2022  M2.2 INCH        ANCHORAGE          AK   TRAINED SPOTTER

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1007 PM AKST THU DEC 1 2022

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

0445 PM     NON-TSTM WND GST 22 E VALDEZ             61.17N 145.70W
12/01/2022  E70 MPH          CHUGACH            AK   DEPT OF HIGHWAYS

            WHITEOUT CONDITIONS FROM SNOW ON THE GROUND
            BEING LOFTED BY WINDS. TIME OF REPORT
            ESTIMATED.

&&