Gale Warning 219, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 AM AKDT Sun Mar 20 2022

.ANALYSIS AND UPPER LEVELS...

A highly amplified pattern is in place over Alaska. An upper level
ridge is present over the Western Bering and is slowly pushing
eastward into the Central Bering. A longwave trough extends
across mainland Alaska and into the North Pacific. Shortwaves
embedded within this trough are producing snow showers along the
northern Gulf and Kodiak Island, as well as along the Alaska
Peninsula. Showery conditions are also present over the Bering
Sea, where northerly flow is producing cloud streets and gusty gap
winds through the Aleutians. Gusts 50 kt and greater have been
observed overnight along the Eastern Aleutians and western Alaska
Peninsula, where the east-west pressure gradient is strongest.

&&

.MODEL DISCUSSION...

Model guidance remains in good agreement through Monday night.
Although model agreement is improving, some discrepancies remain
as a North Pacific low enters the Gulf from Monday night through
Wednesday morning. The GFS and NAM seem to be coming into better
agreement, though there are still differences in the low track and
precipitation amount. The Canadian, in contrast, moves the low
into the Gulf more quickly and is slower to bring the front into
the western Gulf. This uncertainty will primarily affect the
precipitation forecast, with greater impacts along the coast as
less precipitation is expected inland.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

A vertically stacked low over the Gulf will begin to slide to the
southwest today as an upper-level ridge builds over Northwest
Alaska and a secondary area of low pressure moves from the north
Pacific to the eastern Gulf. Shower activity across the Gulf and
Kodiak Island will continue today as easterly waves rotate around
the vertically stacked low. A second easterly wave over the
Copper River Basin is also producing enough lift for some light
snow over the region. This area of snow will shift to the
southwestern part of the basin later today as a northeasterly flow
develops. Additional accumulations for the favored upslope areas,
including Eureka, are likely through late tonight.

The eastern Gulf low is then expected to retrograde to the west
while weakening into an inverted trough. As it does, expect
another area of showers to move across the northern Gulf. The
increased gradient between this feature and a surface ridge
building over the Yukon Flats, coupled with cold air advection,
will also drive northerly winds through favored gaps within the
interior as well as along the coast. The trough will continue to
weaken as it moves to Kodiak Island by early Tuesday morning. Also
by Tuesday morning, a frontal system associated with a deepening
low over the southern Gulf will move to the northern Gulf. This
feature will bring precipitation to the Southcentral coast by
Tuesday afternoon while also allowing gap winds to persist.

&&

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

Dry northerly flow will persist through Tuesday with some
occasional cloud cover. Brisk winds are expected mainly along the
Kuskokwim Delta Coast with occasional higher gusts the next
couple days. This will lead overnight wind chills to be around -20
degrees Fahrenheit through the next few nights. Essentially, a
much quieter forecast is expected with colder than normal
temperatures through at least Tuesday night.

&&

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

Widespread gales with northerly wind direction will linger across
the eastern Bering and Aleutians as well as the AKPen with snow
showers through at least Monday. The snow combined with strong
winds will create areas of blowing snow across the eastern
Aleutians and southern AKPen with a Winter Weather Advisory in
effect until 10 am this morning for the Alaska Peninsula.

Anticipate storm force gusts of 50 to 60 mph south of the eastern
Aleutians and AKPen through today as cold air enhances the winds.
A strong high pressure ridge over the western Bering and
Aleutians will slide to the east and become a blocking high over
the north and central Bering Sea by Monday and Tuesday. Meanwhile
a strong front will move across the western Aleutians by Sunday
afternoon and evening, bringing Gale force winds and rain mixed
with snow. This front will slowly move towards the central
Aleutians and Bering through Tuesday with gale force winds
weakening a bit by Tuesday.

&&

.Marine (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska: A fairly active pattern is expected across the
Gulf of Alaska during the 3-5 day period as two low pressure
systems move through the area. The first low will produce areas of
gale force winds across the northern Gulf on Tuesday. Winds will
ease to below gale force Wednesday morning. The next low will move
through on Thursday and is expected to produce widespread gale
force winds across the northern Gulf on Thursday. Forecast
confidence is moderate on Tuesday and Wednesday and becomes low
on Thursday with respect to the exact placement of gale force
winds. These differences in the exact location of the gale force
winds are a result of differences between guidance with respect
to the position of each low.

Bering Sea: Forecast confidence remains moderate during the 3-5
day period as a series of troughs move across the eastern and
central Bering/Aleutians. Winds will generally remain under gale
force, though there is a chance for localized areas of gale force
winds in the central Aleutians. Gale force northwesterly gap winds
are likely across the central and eastern Aleutians due to the
localized funneling of winds. Freezing spray is also a concern for
the eastern Aleutians as strong cold air advection is expected
across the area.

&&

.Long Term Discussion (Days 4 through 7: Wednesday through
Saturday)...

The pattern is expected to be highly amplified as a Rex Block is
expected to form across the Bering Sea, Alaskan mainland and Gulf
of Alaska Wednesday through Saturday. There is good ensemble
agreement that the center of the upper low that is associated with
this block will remain west of the Kenai Peninsula and the
surface low appears to linger in the northern Gulf east of Kodiak.
This will allow for warmer temperatures in Southcentral as warm
southeasterly onshore flow is expected. This pattern is also
conducive to warmer temperatures in Anchorage due to Chinook winds
off the Chugach Mountains. With respect to Turnagain Arm winds,
the ageostrophic component to the wind will support down-inlet
flow and make it less likely for these Turnagain Arm winds to bend
into Anchorage. The strongest winds are expected Wednesday afternoon
through Wednesday night as the trough-axis associated with the
surface low moves northwestward through the area. These winds will
persist through Friday and then ease on Saturday as the surface
low moves farther south. The biggest forecast challenge will be
precipitation amounts and precipitation type Wednesday afternoon
through Wednesday night. Rain is more likely in low lying coastal
areas and snow is more likely in the mountains and inland areas.
Exact precipitation amounts are another challenge due to uncertainty
in the strength of the downslope forcing off the Chugach Mountains.
Temperatures are expected to remain cold across Southwest Alaska
as cold and dry offshore flow is expected to persist across the
area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 181.
MARINE...Gale Warning: 155, 170-174, 177, 178, 411, 414.
		 Heavy Freezing Spray: 160, 165, 179, 180, 412, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KC
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...ED