Gale Warning 209, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
803 PM AKST Thu Mar 3 2022

.ANALYSIS AND UPPER LEVELS...

A weakening low in the western Bering continues to spread light
snow over regions of the western and central Aleutians. Another
surface low near the Eastern Aleutians is tracking towards
Southwest today. The low’s circulation is tapping into colder
air along its backside and warmer Pacific air along its
southeastern periphery creating areas of widespread snow and rain,
respectively. As this wind-wrapped low tracks towards Bristol Bay
for tonight, it will spread sustained gales and storm-force gusts
mainly south of the low from Unalaska north of the Alaska
Peninsula. An associated deepening upper-level low is becoming
more negatively tilted along its track and is aiding in the
surface low’s amplification today and into tonight.

Out east, a compact upper-level shortwave and trough are tracking
northeastward from Kodiak Island across the Kenai Peninsula and
will pass east of Prince William Sound for tonight. As a result,
snow lingers along the Southcentral coast today while a weakening
front continues to push inland. Northwestern Prince William Sound
is seeing the greatest precipitation amounts with these features
today.

&&

.MODEL DISCUSSION...

The easiest way to assess the models and subsequent forecast
confidence today is to look at things temporally. Starting with
today's developing low near the Eastern Aleutians/Bristol Bay, the
models are in near lock-step at this point. They all resolve the
track in similar fashion having it make landfall near north of
Cape Newenham early Fri morning. Overnight, the models all trended
slightly weaker. So the central pressure now generally only drops
to about 975mb. Some subtle questions still centered on this
storm as exactly how strong the winds will get from Dutch Harbor
into SW AK. Due to the slight weakening in the overnight runs, we
have generally held the winds the same strength or slightly weaker
with this forecast package. As this front washes across southern
AK, it is starting to show signs of bringing quite a bit more wind
across the Anchorage Bowl and the Mat-Valley. We have used hi-res
data to increase gusts across these areas on Fri.

The next system of concern moves up from the Gulf of AK on Sat.
This will bring deep southerly flow with abundant moisture. The
synoptic set up looks very similar among the models, so confidence
in the overall pattern is high. However, the important aspect is
that the overall trend with this pattern has been to the west.
This could shift the rain/snow line further west and inland, to
include parts of Anchorage. A surface low will develop near the
Eastern Kenai Peninsula and its exact track will be highly
important. So the main question surrounds whether or not
precipitation starts as rain or snow. Even if inland locations
start with some rain, they should change over to snow as all
models agree on colder air filtering in.

&&

.AVIATION...
PANC...Winds will be the key aspect to this TAF package. The
Turnagain Arm winds will start to increase through this evening.
As a front lifts over the area late tonight, gusty SE winds should
start at the terminal right around midnight. Winds should then
intensify through the early morning hours. The timing might very
by a few hours. The strength of gusts remain hard to nail down and
could actually be a bit stronger (40-50kts). VFR conditions will
prevail even with some passing showers.

&&

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

An upper level ridge returning over the Pacific with a vertically
stacked low nearing Bristol Bay turning northward tonight toward
the YK Delta will tighten the southeast to northwest pressure
gradient after midnight tonight into Friday morning. Winds through
Turnagain Arm will increase overnight. Sounding profiles show winds
peaking over 60 kts around 1500 to 2000 feet with a well mixed
layer that could bring some of those gusts to the surface. Some
minor discrepancy in the models for the peak winds with the GFS
being an outlier, however, the Anchorage Hillside and Turnagain
Arm could experience the highest winds Friday morning up to 65 mph
and the Anchorage Bowl, including the airport could still expect
strong, gusty winds to around 45 mph. As winds diminish in the
afternoon, strong winds may linger awhile longer in the Matanuska
Valley, particularly the Knik River Valley and Palmer areas.

Southwesterly flow will continue through Southcentral, but an
embedded trough and associated surface low will move towards
Kodiak Island late Friday night and near the Kenai Peninsula Saturday
morning. This could potentially bring a substantial amount of
precipitation across Southcentral and especially along the Gulf
coast through Sunday morning. This is a tricky forecast as storm
totals may vary until the placement of the low is more certain and
dialing in how warm the temperatures will become in the
afternoon. Some downsloping at the onset of precipitation is
possible for the Anchorage area but wrap around precipitation
could bring a few inches through Anchorage area Saturday
afternoon. There does not seem to be much of a threat for freezing
rain as the entire column is well saturated in the snow growth
layer, but any rain on freezing surfaces can not be ruled out.
Also, for the surface to mid-layer profile temperatures, a slight
warm nose or even slightly above freezing temperatures near the
surface may cause a mixture of rain and snow, but the potential
for wet bulbing snowfall exists and could lead temperatures to
cool near the surface with the heaviest bands of precipitation and
switch any rain and or mix over to snow. The Copper River Basin
is another area that could see changes in precipitation type
throughout the day Saturday. Snowfall threat will move east and
diminish through Sunday morning. Brief clearing and a weak ridge
may follow on Sunday and Sunday night, but model certainty falls
apart quickly with the following North Pacific low.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - This
afternoon through Sunday)...

A strong low pressure system will approach the area tonight from
the south. This will bring snow and blowing snow to the area with
some areas around Bristol Bay seeing all rain or a rain/snow mix
especially near the coast and west of the Aleutian/Alaskan Range
where downsloping will keep these areas warmer. However with
downsloping areas like Bethel, Iliamna and King Salmon with see
only light amounts of precipitation. This low pressure system has
been producing wind gusts of 50 to 60 mph along the southern AKPen
today. These strong winds will spread into the northern AKPen and
Southwest Alaska this evening and tonight with 50 to 60 mph gusts
likely in many areas, especially across coastal locations and
Bristol Bay. Snow and blowing snow will develop across the
Kuskokwim Delta especially west of Bethel as the low tracks north
tonight. A Winter Weather Advisory is in effect for coastal areas
of the Kuskokwim Delta with 1 to 4 inches of accumulations. Across
Bristol Bay areas north and west of Dillingham may see occasional
periods of blowing snow along with snow mixing with rain in some
areas. As the low moves north of the area Friday morning, strong
south to southwest winds will gradually weaken by the afternoon
and evening hours across the area. These winds will keep
temperatures in the 30s across much of the area. Saturday a weak
low pressure system will track towards the Kuskokwim Delta
bringing areas of light snow with minimal accumulations. A low
pressure system will also develop south of the AKPen Friday night
and move north towards Kodiak Island and may spread some light
snow across portions of the AKPen and western Bristol Bay with
some light accumulations possible. As we head into Sunday high
pressure will build across Southwest Alaska with cooler
temperatures and mostly clear skies. There is a chance of fog
Sunday morning, but too much uncertainty this far out to mention
it in the forecast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2 -
Today through Friday night)...

A strong low pressure system currently near Unalaska will move
north across the far eastern Bering and into Southwest Alaska by
Friday morning. This will bring a wide swath of gales with
pockets of storm force winds especially south of the low just
north of the AKPen tonight. By Friday afternoon the winds will
weaken to small crafts near the coast of Southwest Alaska. A
compact low will move across the Bering Friday into early Saturday
enhancing winds to small crafts and possibly near Gales in a very
small area. By Saturday high pressure develops across the eastern
Bering as a gale force low and frontal system moves north across
the western Bering. This low will move north on Sunday out of the
area with gales decreasing in strength and areal coverage.

&&
.Marine (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: A northern Gulf low moves along the front to exit
the Southeast Gulf for Tuesday. Forecast confidence is good.
Gusty southerly winds accompany the front into the eastern Gulf.
High end westerly gales extend from Kamishak Bay through the
Barren Islands into the Gulf, diminishing Monday, but return on
Tuesday. Gusty winds south of Kodiak Island extend to the Alaska
Peninsula Coast through Tuesday. Seas building to 18 feet from the
Alaska Peninsula Coast through Tuesday.

Bering Sea: A strong western Bering low moves into the Chukchi
Sea by Tuesday. Its front extends through the central Bering and
Aleutians through Tuesday. Forecast confidence is good. This wind
wrapped low and front brings high end gales, diminishing Monday.
Seas to 22 feet, subsiding. A new well developed low and front
approach the Western Aleutians and Bering for Tuesday. Gusty
winds increase to southerly high end gales with areas of storm
force winds spreading into the Central Aleutians and Bering,
diminishing late Monday. Seas building to 28 feet over the
Aleutians and Bering, subsiding Tuesday.

&&

.Long Term Discussion (Days 4 through 7: Monday through
Thursday)...

At the onset of the forecast period, the longwave pattern will be
amplified. Monday expect a ridge over the east Pacific and a
ridge over the eastern Bering with troughs over mainland Alaska
and over the Western Aleutians. As the forecast period unfolds,
the east Pacific ridge will get shunted but the ridge that was
over the Eastern Bering will move over Mainland Alaska. All the
while there will be a broad area of troughing over the Pacific
Northwest, Western Bering and Kamchatka. The models show negative
height anomalies at 500 mb over the Western Bering and NW Pacific
for much of the period. Whereas, the models have positive height
anomalies over the Chukchi Sea, mainland and the Gulf of Alaska
through March 11th. A series of lows will rotate through the base
of the Western Aleutians trough likely keeping conditions
generally unsettled into next week from the Aleutians to the
Alaska Peninsula. Above average temperatures should prevail across
much of mainland Alaska through next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 155.
MARINE...Storm: 155-172 180 414.
Gale: 119 130-139 150 175-178 352 411 413.

&&

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