Gale Warning 150, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKST Tue Feb 14 2023

.ANALYSIS AND UPPER LEVELS...
The air mass RGB satellite shows the upper level pattern quite
well this afternoon. Overall the pattern is highly amplified with
a longwave trough centered over the Bering Strait region and a
secondary center within moving from Southwest Alaska into
Southcentral Alaska. There are two plumes of sub-tropical moisture aloft.
The first is sliding eastward toward the Panhandle and was the
fuel for active weather the last two days. The second is spreading
over the western and central Aleutians, associated with a visually
spectacular low pressure system south of the Kamchatka Peninsula.
The low itself was analyzed this morning at 932 mb. The system is
so large that the front extends eastward over the western/central
Aleutians, and will be the focus for active weather for not only
the Bering Sea and Aleutians today and tomorrow, but Southcentral
later in the week.

Currently, a front is moving onto the north Gulf coast bringing
snow from Cordova and Valdez through Whittier. Inland locations
are seeing far less snow. Behind that system, arctic air is
filtering through the Southwest Mainland. Out west, the front is
bringing high winds, snow, and blowing snow to the western
Aleutians.

&&

.MODEL DISCUSSION...
Models are handling the weakening features around southern Alaska
quite will with good agreement for the next 48 hours. However,
further west is a different story. As the Kamchatka low is strong
and large, guidance handles that quite well, however, a new
disturbance will develop along the front in the northern Pacific.
There are mainly placement differences for when the system enters
the central and eastern Bering Sea. Timing and strength are well
agreed upon. The forecast for late week is more uncertain because
of the differences but it does look like there is good agreement
in development of a stronger distinct low center in the vicinity
of the Pribilofs. The GFS is currently the model of choice as it
is the middle ground solution, but also agrees with ensemble mean
guidance across ECMWF/GEM/GEFS platforms.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through
Wednesday morning. Chances for light snow increase around mid-day
Wednesday morning with ceilings potentially in the MVFR range but
more than likely stay VFR with flurries.

&&

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

A low near Kamishak Bay this evening will track south of the Kenai
Peninsula as it pushes its occluded front to the north Gulf coast
tonight. Winds are currently at their peak through Prince William
Sound as the front approaches the coast. As the front moves inland
this evening, winds and precipitation will diminish in intensity.
Light snow showers will linger with weak onshore flow in eastern
Prince William Sound into Wednesday, while a shortwave on the back
side of the main upper trough will keep light snow going over
parts of the western Kenai Peninsula, where 2 to 4 inches of snow
may accumulate between Kenai and Homer. Cold advection coming in
from the west on Wednesday will also contribute to continued light
snow along the Kenai Mountains and Chugach Front Range, including
the Anchorage area. This may produce accumulations up to an inch,
with cloudy skies remaining in place around Cook Inlet.

While snow will taper off for a relatively quiet and dry
Wednesday night, it returns Thursday with a strong shortwave
trough tracking west to east across the state. South to
southwesterly flow will accompany this feature, which will favor
the south and west side of mountain ranges. Lower elevations along
the Talkeetna Mountains and Chugach Front Range, including
Anchorage and the Mat-Su Valleys can expect around another inch of
snow accumulation as a result. Thursday night, a strong low in
the eastern Bering Sea pushes its front into the western Gulf,
where Kodiak looks to be warm enough to see only rain with this
system. As the front moves into the northern Gulf, a colder air
mass from the west cuts off the majority of the stream of warmer
air moving up with the front. As the front reaches the north Gulf
coast, this will keep precipitation as snow for much of
Southcentral, with the potential exception of low elevations
along the immediate coast. Several inches of snow will be possible
over the western half of Southcentral on Friday, as most models
are indicating a weaker cross-barrier flow component in the low
levels (compared to the front this evening), with relatively
moist southwesterly flow in the mid-levels, which may limit the
typical dry downslope hole. However, there is still some
uncertainty with the progression of the front and the development
of a triple point low, which will have significant influence on
the low-level flow and resultant snow totals. Stay tuned for
further refinements to the forecast.

&&

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

A short break in the relatively active pattern is set to begin
overnight into Wednesday as the remnants of the low and front that
moved into the region yesterday shifts from near the northern
Alaska Peninsula and Bristol Bay into the northern Gulf. Another
shot of cold, Arctic air will move in from the northwest as the
low departs and skies continue to clear from west to east as a
shortwave ridge axis moves into place from the Bering. This will
facilitate one more round of frigidly cold lows once again
tonight, namely across the Y-K Delta, where lows will once again
fall to between -10 and -20 Fahrenheit.

The break in the pattern will be quite short, with the next system
moving onto our doorstep by Wednesday afternoon in the form of a
fast moving but rapidly decaying front entering from the eastern
Bering Sea. This will give a quick-hitting round of snow to the
region, progressing swiftly across from west to east from
Wednesday evening into Thursday morning. Most locations will not
see more than 1 to 2 inches of new snow accumulation due to the
fast moving and weakening nature of this next frontal system.

A much more potent low will begin to have more notable effects on
sensible conditions late on Thursday into Friday as it winds up
to storm force out over the eastern Bering and pushes a more
formidable front into the Southwest coast. Multiple impacts
from this low and front will be possible, ranging from snow,
blowing snow and strong onshore winds developing as the entire low
shifts towards the Y-K Delta on Friday. There remains a fair
amount of uncertainty regarding the track and timing of this next
low, so expect further updates to the forecast as details for this
next potentially much more impactful system become better
refined.

&&

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

Whiteout conditions have begun this afternoon across the western
Aleutians as a storm force front accompanied by heavy falling and
blowing snow roars towards the southwest Bering while its parent
Hurricane force low (the one that was analyzed earlier today at
932 mb) is south of Kamchatka. This front will make very quick
progress northeast as it begins to weaken to gale force on
Wednesday. Snow and perhaps some blowing snow will progress out
ahead of the front as it transits the Aleutian Chain, but warmer
air behind the front should change snow over to rain fairly soon
after precipitation onset for any given location from Adak east,
limiting the window for accumulating snowfall. Meanwhile, colder
temperatures will hang on for longer up towards the Pribilofs,
allowing for another brief round of blizzard conditions to develop
as southeast winds and snowfall begin tomorrow morning.
Fortunately, this period of near whiteout conditions will be
fairly short, with the front moving past by the late afternoon and
ending falling/blowing snow. Out to the west, the parent low will
slow down and stall out west of Attu as it begins to slowly fill,
but a core of southerly storm force winds will likely continue to
impact the far western Aleutians through Wednesday.

By Thursday, a potent shortwave trough will move into the central
Aleutians from the North Pacific and begin to develop into a
rapidly deepening, closed low as it enters the central/eastern
Bering and pivots around the still stalled and weakening low
farther west. Uncertainty for the exact strength, progression and
timing of this low remains higher at this time, but there is a
good signal that this low will once again produce at least a
storm force wind field as it deepens and lifts northeast. Very
strong and gusty winds will be possible across the central and
eastern Aleutians south of the deepening low from Thursday night
into Friday, depending again on where the low tracks and how
quickly it deepens. There will also be yet another concern for
snow and blowing snow developing closer to the low's center up
towards the Pribilofs, again depending on the low's track and how
much low level temperatures warm up as the low moves in. Stay
tuned for updates on this next system in the very active pattern
continuing across the Bering through the end of the week.

&&

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

The key features of the long term include a building upper level
ridge over the Gulf on Saturday with a broad upper level trough
over the northern Bering. Initially for the beginning of the
period, the jet stream remains south of the Aleutians and briefly
traverses the southern mainland before shifting south over the
Gulf on Sunday. Nonetheless, a mostly active pattern will continue
into early next week as several North Pacific lows lift northward
into the Bering and the Gulf.

By Saturday night, a fast-moving North Pacific low remains south
of the Aleutians and arrives over the Alaska Peninsula. This low
then tracks northeastward into the Gulf, bringing the potential
for precipitation for the southern mainland - from the Alaska
Peninsula eastward to Prince William Sound coast. Depending on the
position of this low as it reaches the Gulf, precipitation may
spread farther northward into the Susitna Valley and Copper River
Basin.

Moving into Sunday, scattered showers look to persist across the
Bering and Southwestern coast, however both the GFS and EC
advertise a building an upper level ridge over the Bering early
Monday morning. Meanwhile a potent low arrives over the western
Aleutians and is quickly driven into the northern Bering by Monday
night. If this setup pans out and the ridge strengthens as
currently advertised, a highly amplified pattern will take shape
for Tuesday as multiple North Pacific lows are steered into the
Bering. Meanwhile much of the mainland may see calmer (though
likely colder) conditions as offshore flow prevails through late
Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 195.
		 Winter Storm Warning 191.
MARINE...Gale 119 130 170 172-176 179 185.
		 Storm 177 178.
		 Heavy Freezing Spray 130 138 150 160 165 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...KO