Small Craft Advisory 219, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
540 AM AKST Sat Mar 12 2022

.ANALYSIS AND UPPER LEVELS...

The majority of Southern Alaska sits between multiple upper-level
systems, which is resulting in a generally unorganized flow
across much of the domain. An upper-level trough associated with a
much colder airmass extends along an axis from northern Canada
southwestward over the Alaska-Yukon border. A broad upper-level
low is extending over the Aleutians and North Pacific. Radar
returns show light snow falling over the Copper River Basin early
this morning with scattered rain showers over much of Prince
William Sound. Nighttime Microphysics satellite imagery reveals a
blanket of low level stratus covering most of the Bering. Farther
west across the Aleutians, several upper-level waves have kept
light showers in place.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement. However, by
Sunday models spread begins to increase. Some timing differences
arise with an upper-level shortwave that moves north to south over
Southcentral. The GFS, is a faster solution and tracks the
shortwave over the Gulf. Whereas, the NAM keeps the shortwave
stationary over Southcentral. A North Pacific low will track into
the southeastern Gulf by Monday. Models have been slowly coming
into better agreement with this low, however, the NAM still
remains an outlier with a faster, and slightly more northerly
track.

&&

.AVIATION...
PANC...Light winds and VFR conditions will persist throughout the
day. Northerly winds will begin to increase tonight with gusts up
to 30 mph.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Today through Sunday
Night)...

An upper level col is directly over Southcentral. Upper level
waves are attempting to approach from both the northwest and
southeast, which is keeping cloud cover plentiful this morning.
However, those clouds are not producing meaningful precipitation
except along the Gulf Coast. All of the clouds are very slow
moving due to the lack of upper level flow.

Mountain high-elevation snow showers and low-elevation rain
showers will persist through the day due to the convergence of
the aforementioned upper level waves. The light precipitation
activity will persist along the Gulf Coast through Sunday night. A
large strong upper level low will move into the southern Gulf on
Sunday, then slowly moves into the eastern Gulf on Monday.
Meanwhile a much colder air mass from Canada will begin to move
into the Copper River Basin today and will really settle into the
Basin tonight. The cold air will filter through the gaps, namely
the Matanuska Valley and Thompson Pass. This will result in gusty
winds in these areas tonight which will persist through Monday
night and beyond. The low in the Gulf will further enhance the
pressure gradient especially Sunday through Monday, resulting in
even stronger winds. Expect gusts to 45 mph through the Mat Valley
and Thompson Pass with these winds. Fortunately with the col being
very slow to move, there won't be any upper level support that
would otherwise have brought concern for damaging winds in these
areas.

A much more significant cold air surge will move into the area
Monday night. This will shift the strongest gap winds to the
northwest, moving through the Alaska Range, which in turn will
diminish the other gap winds a bit, though it will stay gusty.

Both cold air surges will also have the effect of drying the area
out and clearing the abundant moisture that is currently stuck
over Southcentral. The cooling temperatures will also reduce the
daily melting, though the strong March sun will still do a bit of
melting on south-facing surfaces in the afternoons even despite
expected sub-freezing air temperatures. The drying out will also
allow for a few beautiful, if cool, sunny days Sunday through
Tuesday for most of the area.

Looking ahead, guidance is in quite good agreement that a strong
upper low barrels over Southwest Alaska Tuesday. This will cause
the flow to turn southerly in the upper levels over Southcentral,
which will draw a North Pacific low into the area. This presents
the next opportunity for snow, and perhaps significant amounts of
it, on Wednesday. Stay tuned!

&&

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

Cold air advection combined with upper-level ridging will
provide much cooler temperatures and mostly clear skies over most
parts of the region into Monday evening. An upper-level trough
sliding southward from the interior could potentially invite
increased clouds and light snow starting this evening into Mon
morning followed by the aforementioned ridge axis. Overall,
anticipate a quiet forecast.

&&

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

An upper-level low near the Aleutians combined with an upper-
level trough exiting the Southwest Coast will aid to bringing
periods of unsettled weather for the region through the short-
term. These separate features will take their time transiting
through the Bering, which could potentially lead to increased
formation of additional upper-level lows near the Aleutians and
over the central/western Bering by Mon. Strong winds extending to
the NNW of Pribilof Islands and declining temperatures aloft will
favor heavy freezing spray over parts of the central Bering and
mostly WSW of St Matthew Island through the short term.

&&
.Marine (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska: A low of about 975 mb will center over the Gulf
on Monday. Moderate confidence in the placement of this low as it
moves towards the southeastern Panhandle through Tuesday and the
trough elongates along the Gulf coast. Winds could reach around 30
kts in the northern Gulf. Another low approaching closely behind
from the North Pacific will interact with this initial low by
midweek. The speed of this low and how this interaction evolves
has lower confidence. Northerly flow, along with offshore flow and
cold air advection, could increase winds through gaps and bays
near the Alaska Peninsula and the eastern Aleutians on Tuesday
afternoon and Wednesday. Seas up to 15 feet Monday will subside
Tuesday and up to 10 feet on Wednesday.

Bering Sea: Offshore flow and cold air advection is expected
Monday and Tuesday as a low track remains south of the Aleutians.
Flow becomes more northerly Tuesday afternoon and Wednesday with
high pressure building over the western Bering. This will help
tighten a pressure gradient over the eastern Bering and Aleutians
that will increase winds to near gale force late Wednesday. Seas
up to 8 feet on Monday over the western Bering. Seas build through
the first half of the week across the entire Bering to around 12
feet midweek under northerly flow in the eastern Bering.

&&

.Long Term Discussion (Days 4 through 7: Tuesday through Friday)...

A transition to a cooler than normal regime is expected next week
as offshore flow increases with cold air advection. Winds may
increase through wind prone north-south gaps midweek, particularly
over the western Gulf, the AKPen, and eastern Aleutians. Snow
showers are expected across the Aleutians Tuesday with northerly
flow. High pressure will build beginning over the western Bering
on Tuesday night and move eastward through the rest of the week
with another low filling in to the west towards the end of the
week. The evolution of surface features make the location and
timing of snow showers this upcoming week more unclear. Exact
placement of the low over the Gulf on Tuesday will determine the
timing and onset of precipitation along the Gulf coast and the
subsequent spreading across Southcentral. By Wednesday afternoon,
widespread snowfall is expected across Southcentral. This low
appears to circulate through the Gulf again, but the details
remain uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 127, 130, 138, 150.
		 Heavy Freezing Spray Warning: 180, 181, 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...NS
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...MK/VR