Gale Warning 661, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 AM AKST Mon Nov 16 2020

.ANALYSIS AND UPPER LEVELS...

An omega block pattern is in place across the state of Alaska this
morning. This can be seen when looking at the water vapor imagery
with the 500 mb height fields overlaid from the various models.
Downstream of the ridge is a broad weak upper level low present
over the Gulf of Alaska which continues to dissipate this morning.
The upper level ridge axis is currently over the eastern
Aleutians/Bering Sea northward to the Seward Peninsula of Alaska.
A very strong upper level low with a corresponding surface low is
present near/over Amchitka this morning. These patterns usually
stay in place for a couple of days until they are able to break
down meaning basically the same type of weather can be expected.

The upper level ridge continues to move eastward over much of the
state of Alaska this morning resulting in mostly clear conditions
for much of the southern Mainland. There are some spots still of
low stratus especially in and around Palmer this morning with even
some stratus showing up near Gulkana. With this pattern in place,
the main weather issue across much of the area will be the gap
winds out of bays and passes such as Valdez Arm, Valdez Narrows,
Resurrection Bay, Copper River Delta, Thompson Pass, and
Whitter/Passage Canal. For many of the other areas, where wind is
calm or light and variable, decent radiational cooling is taking
place especially since much of southern Alaska now has a snow
cover. Many areas across Southcentral were seeing temperatures in
the single digits and teens, especially across the Anchorage
Bowl, Kenai Peninsula, and the Matanuska Valley. Palmer's
temperature was hovering in the low to mid teens due to the low
stratus keeping things warmer there while Wasilla was near zero.
Across the Copper River Basin, temperatures have dipped into the
teens below zero this morning. For Southwest, temperatures were
mainly in the teens and single digits inland with 20s along the
coast.

Over the Bering Sea and Aleutians, a sub 980 mb low continues to
move its way towards Amchitka and then into the Bering Sea. Latest
ASCAT Scatterometer data is showing widespread gales on either
side of the low pressure center. However, closer to the actual low
center, some storm force wind gusts were occurring with Adak
Station observing 50-55 kt wind gusts overnight. This will
continue pushing eastward into the Bering Sea this morning.
Periods of rain were also accompanying these strong winds as the
low moves through.

&&

.MODEL DISCUSSION...

Model guidance remains in great agreement on the synoptic scale
features for the short term forecast. Current weather data shows
an omega block pattern has setup across Alaska which means that
basically the same weather can be expected for the next couple
days until this block is able to break down. Model guidance keeps
much of the southern Mainland dry and cold for the next couple of
days with gap winds continuing to be the main concern.
Temperatures are also of concern as where winds stay up,
temperatures won't be able to fall as much as if the winds were
light and variable or calm.

Bering Sea and Aleutians: Models agree on another storm force low
moving a front through the Aleutian Chain and the Bering with the
center stays just west of the Bering while moving north towards
east Russia. There still remains some discrepancies on the exact
track and intensity but all guidance agrees on another strong
system for Monday night through Tuesday night. Beyond Tuesday
night, model guidance is locking in another system rounding the
base of the trough into Wednesday that is expected to bring
another round of unsettled weather to the Bering/Aleutians. For
now this looks to be a gale force system, though, storm force
cannot be ruled out.

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through Tuesday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Wednesday night)...

A strong blocking ridge to the west will provide seasonably cold
and dry conditions to Southcentral as we head through the first
half of the work week. Deep northerly flow with higher pressure
to the north and west and lower pressure over the Gulf will
continue to produce gap winds along the coast. Pressure gradients
will slacken today, allowing these winds to weaken a bit.
However, winds will begin to ratchet back up Tuesday through
Tuesday night as a deep low tracks toward Southeast Alaska,
supported by rapidly tightening pressure gradients and
strengthening offshore flow at all levels. Forcing looks
particularly favorable for the Valdez area and the Copper River
Delta, so have continued the recent trend of strengthening the
forecast winds for Tuesday night into Wednesday morning. Winds
will then quickly diminish Wednesday afternoon through Wednesday
night as the upper ridge repositions over northern Alaska, low
level flow becomes light and variable, and the low near Southeast
Alaska dissipates. The movement of the ridge will allow a
weakening front from the Bering to reach Kodiak Island by late
Wednesday night, bringing a chance for rain and snow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Monday
morning through Wednesday)...

High pressure has moved into western Alaska with dry and cold
conditions, northerly winds have kept the area fog free for today.
Fog is possible by Tuesday morning with light winds. A weakening
low pressure system approaching from the Bering will bring
increasing clouds and chances of rain near the coast and snow
inland by late in the day on Tuesday, however very little if any
snow accumulations expected as the system weakens over land.
Wednesday a frontal system approaches from the west which will
keep the area cloudy with low chances of precipitation.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Monday
morning through Wednesday)...

A storm force low over the western Aleutians will move towards
the Pribilofs tonight while weakening to gale force. This low
will weaken and dissipate as it moves into Southwest Alaska
Tuesday evening.

The next storm system will move in, with a gale force front
approaching the western Bering/Aleutians early Tuesday. Late
Tuesday/Tuesday night this front moves into the central Bering,
while its parent low with storm force winds moves into the far
western Bering/Aleutians.

On Wednesday, the western Bering storm lifts north/west out of
the region, with winds decreasing to low end gales by late day in
the western Bering/Aleutians. Its associated front heads towards
the Southwest Alaska coast while weakening.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

Gulf of Alaska:
A deep low in Southeast Alaska Wednesday morning will produce
strong gap winds along the Gulf coast and Prince William Sound,
particularly in the Valdez area and out of the Copper River Delta.
Winds will then rapidly diminish Wednesday afternoon through
Wednesday night. The next potential for significant weather will
be Friday, as a front arrives from the Bering Sea. There is some
potential for a low to develop along the front as it nears Kodiak
Island. For now the forecast reflects a small area of gale force
winds over the western Gulf, but this could end up being stronger.

Bering Sea:
A strong Northwest Bering low moves into the Russian Far East Thu,
with its frontal system tracking all the way across the Bering Sea
to the west coast of Alaska. Expect widespread gales initially,
with weakening winds Wednesday afternoon through Wednesday night.
Attention then shifts to a rapidly deepening low just south of the
Aleutians Wednesday night. This low will cross into the eastern
Bering Sea Thursday and looks like it could be quite compact and
potent. The forecast continues to carry gale force winds with
this low, but if current trends hold, will consider upping to
storm force with the next forecast this afternoon.

&&

.LONG TERM FORECAST (Days 4 through 7...Thursday through Sunday)...
This period looks to feature continued relatively cold and quiet
across much of Southcentral with very active weather across the
Bering/Aleutians. This is mostly due to an impressive polar jet
ripping at 150 kt (300 mb/30,000') across the western Aleutians
into the North Pacific. The jet then turns northward near the
Alaska Peninsula, serving to support the surface features over the
Bering. Meanwhile, there is very little jet activity over
Southcentral. Thus, the overall theme will be for strong lows
across the Bering to try to push decaying fronts over SW AK before
they fall apart against the ridge over Southcentral.

On Thursday, a strong low over the western Bering will exit the
area as it moves over Siberia. This will leave widespread cold air
over the Bering providing enough baroclinicity for another strong
system to develop over the eastern Aleutians late Thursday into
Friday. That low moves quickly up the West Coast while weakening
on Friday. By early Sat, 2 more lows show signs of developing. 1
is way out over the Western Bering while the second one is near
the Alaska Peninsula/Kodiak. There is still plenty of model
uncertainty with the exact strength and location of each of these
systems, but in general, a GFS/EC blend was preferred.

By late next weekend, it does appear that things become slightly
more progressive from west to east over the mainland. This could
open the possibility of a Gulf low inching closer to the
Southcentral coast as well as allowing a front from SW AK to make
it over the Alaska Range. For now though, the forecast looks
mostly dry.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Special Weather Statement 145.
MARINE...Storm Warning 178
Gale Warning 411 412 413 414 170 173 174 175 176 177 179.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...MK/MSO/SB