Gale Warning 70, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 PM AKST Sat Jan 21 2023

.ANALYSIS AND UPPER LEVELS...

An amplified upper-level pattern remains across the region today.
An upper-level trough over the Copper River Basin, with lingering
light snow, continues to move east this afternoon along with its
attendant surface low southeast of Kayak Island. Skies are
clearing in the wake of this trough, due to a drier northwesterly
flow between it and a transient upper-level ridge lifting
northeast from the western Gulf and Bristol Bay. Mainly clear
skies and very cold temperatures prevail across Southwest Alaska
this afternoon as the upper-level trough axis crests overhead.

North to northeasterly winds are also on the increase across
coastal Southwest Alaska today in response to an increasing
pressure gradient between a strong surface ridge over the Bering
Strait and a deepening area of low pressure south of the eastern
Aleutians.

Strong easterly winds and mixed rain/snow are also occurring
across the eastern Aleutians this afternoon as occluded front
associated with the surface low lifts north toward the Chain.

Elsewhere, easterly winds are also beginning to ramp up across
the Pribilof Island this afternoon. Westerly winds and occasional
snow showers persist across the western Aleutians as colder air
wraps underneath a compact surface low northwest of Shemya.

&&

.MODEL DISCUSSION...

Models are in generally good agreement with respect to the
synoptic-scale features through the next several days. More
noticeable differences begin to arise by Monday as the long-wave
trough undercuts the upper-level ridge and elongates over the
eastern half of the Aleutians and the western Gulf of Alaska. The
differences are mainly in the position and strength of various
shortwaves as they move through the trough. Even with these subtle
differences, guidance continues to advertise the development of a
southwesterly flow transitioning to a more southerly flow by late
Monday as the upper-level pattern becomes highly amplified once
again. Guidance is all showing this amplification resulting in
deep moisture advection and warmer air moving over the Southern
Mainland for early next week. When and where precipitation types
will transition between frozen and liquid will be determined by
the tracks of the various shortwaves.

&&

.AVIATION...
PANC...VFR conditions and northerly winds will prevail through
Saturday evening. The northerly winds are expected to diminish
slightly tonight and remain light through Sunday morning. Areas of
fog and/or low stratus may move over the terminal Saturday night
through early Sunday morning. While confidence is low given the
drier airmass advecting over the region, temperatures and moisture
in the boundary layer are expected to increase overnight. The
trend of moderating temperatures in the lower levels may be just
enough to trap any lingering low-level moisture and support the
development of fog and/or low stratus.

&&

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

A low along the immediate Gulf coast just west of Yakutat has
pulled in dry air from the northwest, leading to clear skies for
the eastern portion of Southcentral, while clouds and snow linger
in the Copper River Basin. Clearing overnight will allow
temperatures to drop into the teens to single digits for most
areas, while the Gulf Coast and Sound remain in the 20s to low 30s
once winds diminish.

The colder airmass will be short lived as a series of progressively
warmer systems moves into Southcentral through midweek next week.
The first front will reach the Gulf Coast and Prince William
Sound early tomorrow morning returning snow to sea level initially
before snow levels gradually rise to around 500 ft by the afternoon.
With decent cross-barrier flow, most of the population centers of
the Western Kenai north to the Mat-Su will remain downsloped for
this event.

On Monday an additional upper low will pivot north into either
Southcentral or the northern Gulf. There remains some uncertainty
in where this feature will set up, which will change the low
level wind field and subsequently the precipitation type forecast
for Cook Inlet areas and the Mat-Su Monday afternoon. It does
look like sometime late Monday and into Tuesday morning winds will
shift to southerly, switching any precipitation falling as snow
or a wintery mix to all rain. Temperatures after the winds come in
will likely move into the mid 30s for areas south of Willow,
while the northern Susitna Valley will likely hold onto colder
air. Flow aloft will also switch from southeasterly on Sunday to
south-southwesterly on Monday and Tuesday. This will provide good
upslope conditions for the northern Susitna Valley, Eastern
Alaska Range, and Talkeetna Mountains. Farther east, warm air is
likely to make it a decent ways into the Copper River Basin, where
Glennallen could move above freezing. Freezing rain also can't be
ruled out along the Edgerton Highway east into McCarthy. Stay
tuned.

&&

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

Clear and cold and windy conditions tonight will moderate somewhat
as a front from the Aleutians pushes northward. Northerly winds
will increase as the front approaches, bringing the threat for
blowing snow from the Kuskokwim Delta through Bristol Bay with
some visibility reduction. The front will bring some warmer air
over the region temporarily leading to warmer overnight low
temperatures tonight and high temperatures Sunday. While
weakening, the front will bring a chance for light snow to mainly
the greater Bristol Bay area. A better chance for snow will come
into play Monday afternoon into Tuesday as a disturbance progresses
along said front with the best chances for snow being from
Bristol Bay through the Kuskokwim Valley. Colder air and northerly
winds will remain entrenched for the Kuskokwim Delta keeping wind
chills in the -15 to -30F range through Tuesday.

&&

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

A storm-force front will continue to push northward across the
Aleutian Chain into the southern Bering Sea tonight. Winds will
peak in the early evening where a High Wind Warning is in place
for the Eastern Aleutians. Despite the front weakening as it
moves northward, several disturbances will combine with the front
to make for a period of falling and blowing snow for the Pribilof
Islands where a Blowing Snow Advisory is in place Sunday afternoon
through Monday afternoon. As arctic air continue to flow across
the Bering Sea from the north, extreme freezing spray is possible
closer to the sea ice edge where the best combination of
winds/waves/temperatures exists. Expect icing rates of 4 cm/hour
or greater.

&&

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

Agreement between the deterministic models in the extended period
remains loose, continuing the low-to-mid forecast confidence for
this timeframe. Wednesday morning, a low looks to enter Southern
Alaska. However, further placement of this low remains difficult
to determine. The GFS places this low at the Southwestern edge of
the Alaska Peninsula Wednesday morning with a front extending
northeastward moving over Southcentral. In contrast, the Canadian
and Euro models place the low center over Kodiak Island Wednesday
morning. Furthermore, the 12Z GFS moves a Northeastern Pacific low
rapidly through the Gulf into coastal Southcentral by Thursday
morning, a feature not represented by the equivalent Euro/Canadian
runs. These disagreements have made the wind field, and resultant
weather inland difficult to determine at this time. Following
this agreement is good that moderate ridging will begin to develop
over Eastern Alaska, diminishing activity for the area through
the weekend.

Out west, agreement is fair that a North Pacific low will move in
west of Attu with a long front that will sweep the Chain eastward
beginning Wednesday morning reaching Southwest Alaska by Saturday
morning with diminished intensity. Strong precipitation currently
expected along the boundary of the front, with lingering showers
behind throughout this period. Gale-force southerly winds will
advance eastward with the frontal boundary, with Storm-force winds
currently possible Wednesday morning as the front clips the
western-most Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 185.
         Winter Weather Advisory 195.
MARINE...Heavy Freezing Spray Warning 160 179 180 185.
         Storm Warning 170 172 173 174 179.
         Gale Warning 119 120 130 131 132 138 139 150 155 160
                      165 171 175 176 177 178 180 181 185.
FIRE WEATHER...NONE.

&&

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