Heavy Freezing Spray Warning 50, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
622 PM AKST Mon Feb 1 2021

.ANALYSIS AND UPPER LEVELS...
The cold upper low over the Yukon territory of Canada continues to
drop slowly south. A strong 130 kt northwest jet extended south
across Southcentral with dry air intrusion evident on water vapor
imagery. At the surface, the arctic airmass has spread over much
of Southcentral Alaska with many areas in the single digits to
below zero, warmest in windy areas. Sharp thermal/pressure
gradients between the cold continental air and relatively warm
Gulf air accompanied by low to mid level wind support has given
rise to wingspread gusty winds across much of Southcentral.
The strongest winds with gusts in the 60 to to upper 70 mph range
were evident from Thompson Pass to Valdez. Winds with cold
ambient temps produced low wind chill across many areas.

Out west, the frontal system over the eastern Aleutians is slowly
marching eastward bringing rain and windy conditions over the
eastern Bering Sea and snow and blowing snow to the Kuskokwim
Delta. Satellite imagery shows showery conditions to the west of
the front zone.

&&

.MODEL DISCUSSION...
Models are in general synoptic agreement. Minor differences will
be handled with hand edits and high res models.

&&

.AVIATION...
PANC...VFR conditions continue. Gusty northerly winds will
diminish overnight.

&&

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

An upper level ridge to the west with an arctic low moving into
Southeast Alaska is creating a strong pressure gradient and cold
air advection driving gusty winds through the gaps with wind
chill advisories for Thompson Pass through noon tomorrow. The
High wind warning remains in effect for Thompson Pass through 10
PM tonight. Winds will be very gusty in Valdez with gusts up to
65 mph as well as through the Copper River Delta. Seward and
Whittier are not quite as windy but still getting occasional
gusts into the 40 mph range. The winds across the Matanuska Valley
also started early today and will continue through tomorrow
afternoon. They should be strongest overnight with gusts of 50 to
60 mph. By tomorrow afternoon and evening most of the winds will
decrease as the pressure gradient loosens up and the cold air
advection ends.

Our focus then turns to an upper level shortwave moving towards
the area Tuesday into Wednesday. This will support a weak front
pushing through Kodiak Island bringing mainly snow, but may
change to a rain/snow mix at Kodiak City by the afternoon and
evening hours of Tuesday. Tuesday evening the front moves north
into the Kenai Peninsula with periods of light snow. During the
overnight hours into Wednesday morning the upper shortwave may
bring periods of light snow from Anchorage into the MATSU Valleys
with generally accumulations less than 2 inches. The light snow
will also spread into the Copper River Basin Wednesday with only
minor accumulations expected. Overall this system will have
minimal impacts, however some uncertainty remains on timing and
snow amounts so stay tuned.

Finally, the ridge builds back in over the area on Thursday with
clearing skies and light winds.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Monday to
Wed morning)...

A band of mixed precipitation ahead of a front is just beginning
to work ashore as it meets a cold air mass in place across the
Y-K Delta. Gusty offshore winds are driving areas of blowing
snow, especially near the Bering coastline. Winter Weather
Advisories are in effect from this evening through Tuesday
afternoon for both the Y-K delta and Bristol Bay for the potential
for a wintry mix of sleet, snow and freezing rain transitioning
to all snow later on Tuesday morning.

The main concern with this event is shifting more towards the
falling and blowing snow, and both observed and forecast
soundings indicate the warm nose moving in ahead of the boundary
is only slightly above freezing and very dry. Thus, it appears
likely most locations outside the immediate Southwest coast will
see precipitation begin as either all snow, or a mix of sleet and
snow transitioning rapidly to all snow by the middle of Tuesday
morning. This will result in somewhat higher snowfall totals
across Bristol Bay than earlier anticipated, with up to 7 inches
of accumulation possible between Togiak and Dillingham. Snowfall
totals across the Y-K delta are expected to range from 4 to 8
inches with the heaviest amounts along the coast between Hooper
Bay and Kipnuk. Snow will end from southwest to northeast as the
front moves inland between Tuesday afternoon and early Wednesday
morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Monday
to Wed morning)...

A front will continue to bring rain and a wintry mix of sleet,
freezing rain and snow over parts of the far eastern Bering
through Tuesday morning. Winds are continuing to weaken to mainly
small craft and low end gales with this front as it pushes closer
to the Southwest coast. After a brief lull in the weather, another
front extending from a low moving over the Kamchatka Peninsula
will approach the Western Bering/Aleutians by Tuesday night and
bring gale force winds and a mix of rain and snow as it moves
across the Western Bering and Aleutians through Wednesday.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Gulf of Alaska: Gusty northwest outflow winds across the Barren
Islands and Kamishak Gap are possible Thursday morning. By
Thursday night, an approaching low will lift northward and tighten
pressure gradients. This will increase winds to gale force for
Friday. There is the potential for storm force winds with this
front, though models are inconsistent with the strength of the low
at this time. Broad low pressure will be in place across the Gulf
Saturday with residual gale force winds possible.

Bering Sea: A gale force front will be stalled over the central
Bering Thursday. By Thursday night, there is increasing confidence
that a strong low will approach the Western Aleutians with storm
force winds possible, however confidence remains low regarding
where this storm will track. Meanwhile a North Pacific low will
lift over the Alaska Peninsula/eastern Bering Friday. This will
introduce gale force winds to the eastern Bering waters Friday
into Saturday.

&&

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

The long term pattern features a ridge extending over the Gulf
and southern mainland that shifts eastward. Upstream, an
elongated upper level low tracks eastward Friday and Saturday. At
the surface, a North Pacific low supported by this trough will
lift northward over the Alaska Peninsula. There is increasing
confidence that this low will strengthen as it moves northward
over Southwest Alaska through Saturday. The associated front
extending across the Gulf will lift northward, reaching the
north Gulf coast by Friday. While confidence remains low on the
exact track and strength of this low, model solutions remain
consistent with this feature, and depict a moisture-laden system
across the southern half of the state Friday into Saturday. In the
wake of this low, a broad trough remains in place over the
western Bering with several additional lows forming along the
Aleutian Chain Saturday into Sunday. By Sunday afternoon, another
low develops over the western Bering, pushing a front eastward
through Monday. Overall, an active weather pattern will continue
through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 131.
		 Wind Chill Advisory: 131.
		 Winter Weather Advisory: 155 161.
MARINE...Gale: 125 127 128 130 177 178 180 411 413.
Heavy Freezing Spray: 121 126-130 139 140 160 180.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...KO