Gale Warning 31, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 AM AKST Tue Jan 3 2023

.ANALYSIS AND UPPER LEVELS...

A broad longwave trough remains nearly stationary over the
eastern Bering and western portion of Alaska with multiple
shortwaves and lows embedded within. Meanwhile, an elongated
trough of low pressure extending from Kamchatka to
the western Bering Sea continues to approach the western
Aleutians. This front has been bringing widespread light
precipitation across the western to central Aleutians and is
expected to persist through this evening. Satellite Imagery is
displaying a gale force North Pacific low tracking into the Gulf
this morning, which will be the next weather maker for the Gulf
and Southcentral today. Depicted on radar, steady light
precipitation continues to fall across much of the Bristol Bay
region due to a weakening low pressure system crossing north of
the Alaska Peninsula and into Bristol Bay. A series of shortwaves
pinwheeling around the low will maintain snow showers across
Southwest Alaska before tapering off this afternoon.

&&

.MODEL DISCUSSION...

Models continue to struggle with how the various shortwaves
embedded in the upper-level flow will impact the forecast area
along with the extend of spill-over precipitation along the lee of
the coastal mountains. However, models are locking onto
a solution with a low entering the Gulf today from the North
Pacific and tracking toward the Barren Islands tonight. Model
spread and forecast uncertainty then rises again in regards to a
second low crossing the far eastern Gulf on Wednesday as well as
out west in relation to a series of lows and how they will impact
the western to central Bering/Aleutians in the coming days.

&&

.AVIATION...
PANC...VFR conditions will persist. A chance for light snow and
gusty northerly winds this evening into tonight is possible as
the Gulf low passes just south of the Kenai Peninsula.

&&

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

An upper level wave is moving from southeast to northwest over
the southern Kenai Peninsula early this morning. The rain in
Prince William Sound is not really associated with this wave but
just a result of upsloping in southeast flow and weak low level
instability. The precipitation resulting from both of these
features should end by this afternoon as there will be downward
vertical motion ahead of the strong low that is tracking into the
Gulf of Alaska from the Southeast. This low is rather impressive
on satellite and is the one the models were having a terrible time
resolving just a day ago. Fortunately, the low is now being
handled quite well now that it has developed and there is much
higher confidence in the forecast as it tracks to the southern tip
of the Kenai Peninsula tonight. The low should then rapidly
weaken as it continues its northwestward track across the Aleutian
Range and into the Bristol Bay region. This will keep most of
Southcentral in southeast-to-northeast flow aloft as the low moves
through. This should keep temperatures mild and most of the
precipitation relegated to coastal mountains as the lee side of
the mountains will see precipitation downslope in this flow.

Yesterday there looked like there could be a secondary low
trailing this large low entering the Gulf of Alaska today. This
looks much less likely at this time and Southcentral should
generally keep Southeasterly flow aloft for Thursday but with
somewhat cooling of temperatures as there will be less cloud cover
and 850 mb temperatures also drop a little by Thursday.

&&

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

Unsettled weather will continue in Southwest Alaska through mid-
week as a weakening low pressure system over Bristol Bay sends
several shortwaves through the area. These shortwaves will bring
showery activity concentrated in the Greater Bristol Bay area
through Tuesday night, however there is a chance for showers to
reach up to Bethel early this week. The resident low pressure will
decay and move out by Tuesday night as a new low pressure system,
approaching from the Gulf of Alaska, will cross the Alaska
Peninsula (AKPen) late Wednesday morning. This new system will be
accompanied by a deformation band along the leading edge which
will bring a more consistent precipitation pattern to Southwest
Alaska, focused mainly in the Greater Bristol Bay area.
Precipitation associated with this system will be snow, with
generally light accumulations of 1-2 inches between Dillingham and
New Stuyahok. Precipitation will return to a showery pattern
north of the AKPen by Wednesday night as the low weakens and exits
to the northwest.

Regarding winds, gusty winds out of the Kamishak Gap into Iliamna
early this morning will ease by this afternoon. This will bring a
return to below freezing temperatures by late today. Steady
offshore flow will establish as the new low moves in from across
the AKPen. As the system exits to the northwest, calm onshore flow
will set-up. With the recent precipitation in the area, the calm
onshore flow creates the chance for patchy fog Wednesday
night/early Thursday morning in the Greater Bristol Bay area which
should dissipate by late Thursday morning.

&&

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

A low over Bristol Bay continues to promote unsettled conditions
for the Eastern Aleutians. A col in the Central Aleutians will
move out as a trough stretching from a low over the Kamchatka
Peninsula has entered the Western Aleutians. This front is
producing precipitation and relatively docile winds. Precipitation
type is to remain snow with a chance for some mixed precipitation
for these systems as resident temperatures across the Aleutians
remain below freezing or near freezing. Due to the lack of colder
air moving in behind the front, gusts are expected to remain
moderate or less. Multiple embedded lows within this front will
break up the structure by tonight, resulting in mild showery
activity from the Western to Central Aleutians through Wednesday
night. Conditions will remain unsettled across the Chain through
Thursday. The next system poised to move in will be a North
Pacific low approaching the Western/Central Aleutians by Friday
morning. There is still moderate model uncertainty regarding the
placement of this system, however, it will bring a shot of
precipitation to the area and is liable to draw several more
shortwaves up along the Chain as it spins in the Bering early this
weekend.

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

Deterministic guidance is in terrible agreement on any discernible
feature in the long range forecast as the region remains under the
influence of a broad longwave trough with many embedded
shortwaves extending from Kamchatka to Southeast Alaska. More of
an ensemble approach is needed in this scenario with only broad
weather characterizations able to be made at this time. Ridging
building over western Canada will promote storm system movement
into the Gulf, bringing continual warm air and above average
temperatures to Southcentral. Precipitation type will remain a
challenge across Southcentral as there is no good signal of cold
air moving back in aloft, supporting rain, mixed precip type or
wet snow at sea level locations. Most guidance indicates that the
storms will remain coastal, with continual precipitation for the
Mountains. For Southwest Alaska, slightly above to seasonal
temperatures appear likely as they will remain closer to the
colder side of the broad trough. Generally, the models keep the
region drier as well, with a few shortwave ridges moving through.
For the Bering, a large conglomerate of small, and occasionally
strong lows will meander across the chain, bringing below average
temperatures and snow showers.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119-120, 125, 130-131, 139, 351.
		 Heavy Freezing Spray Waring: 185.
FIRE WEATHER...NONE.

&&

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