Gale Warning 51, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 AM AKST Fri Jan 7 2022

.ANALYSIS AND UPPER LEVELS...

At 500 mb there is a strong high over Siberia that spans into
Southwest Alaska. There are major shortwaves south of Shemya,
Adak and Cold Bay. On nighttime microphysics satellite imagery
fog is discernible over portions of Turnagain Arm and Knik Arm.
Also on satellite imagery, there is a decaying frontal boundary
north of Adak and a new occlusion south of Adak. The jet is riding
down the east side of the ridge. There is a jet core with a
magnitude of 85 knots moving towards the Copper River Basin.

&&

.MODEL DISCUSSION...

The models are in good agreement with the synoptic pattern through
Saturday, and by Sunday morning they start to diverge on the
evolution of the low pressure areas over the north Pacific. The models
remain on track bringing a fetch of warmer and moister air aloft
into Southcentral this weekend. However, some of the biggest
forecast challenges are actually in the very near term, to include
fine tuning the potential wind event for the Matanuska Valley
this afternoon and Saturday.

&&

.AVIATION...

PANC...The past two mornings fog/low stratus has been detected
over portions of Turnagain Arm. This morning not only is it over
Turnagain Arm, there is also fog over Knik Arm. Expect reduced
cigs at PANC. The situation is being actively monitored and
amendments will be made as needed. Winds will be relatively calm
at PANC until 3z and then gusty northerly winds are possible.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3)...

Areas of fog remain this morning across the Anchorage Bowl and
Copper River Basin as low-level moisture that advected over these
regions today has now been trapped by a deepening inversion. This
inversion is due to continued cooling temperatures at the surface
coupled with weak warm advection with 850mb temperatures climbing
to around -3C, as indicated by the 12z sounding at PANC. These
areas of fog should erode later this morning as an upper-level
wave dives south from the interior of the state.

This feature will help usher in another round of arctic air, as
850mb temperatures drop to -15C across coastal Southcentral and
the Mat-Su Valleys to -28C over the Copper River Basin. The cold
air advection, along with the upper-level support and an increased
surface pressure gradient, will all combine to keep gap winds
quite gusty through favored locations.

One area of focus is the Matanuska Valley, where it looks like
northeasterly winds will again ramp up beginning this afternoon as
the aforementioned wave moves south. Models have backed off on
previously forecasted gusts of around 60 mph. This is likely due
to the strong inversion and stable airmass near the surface that
has developed (see above). The challenge now is whether this
stable airmass will erode and allow winds that will certainly be
increasing aloft to mix down to the surface. Even with colder air
advecting in aloft, this airmass may remain warmer than forecasted
surface temperatures (currently ranging between -5F and -20F). If
so, the strongest winds will likely remain aloft and will only
mix down once the surface warms and the inversion erodes. Given
this added variable and the likelihood for some degree of
inversion remaining in place, at least initially, the forecast
reflects a lowering of winds gusts to around 40 mph for Friday
afternoon and evening. Winds will should then diminish further
Saturday before a second increase in winds, with stronger gusts
possible, into Sunday as a front approaches the northern Gulf and
the pressure gradient tightens.

Over the Gulf, an inverted trough will develop east of Middleton
Island later today and move west across the northern Gulf. Light
snow looks likely for the eastern Kenai Peninsula by Saturday
morning with snow moving over Kodiak Island for Saturday
afternoon. A front associated with a storm-force low in the North
Pacific will then lift a front into the Gulf for Sunday morning
with snow eventually changing to rain for Kodiak City. The front
then moves north by late Sunday as snow and gusty winds overspread
the Southcentral coast. Although there is still quite a bit of
model uncertainty with regard to the track of the low, it does
look like the front will push onshore sometime late Sunday. A
southerly flow behind the front will likely push temperatures
above freezing along the coast, changing snow to rain. However,
measurable snowfall is likely for locations around Prince William
Sound before any potential changeover to rain. Farther inland and
at elevation, the precipitation looks to remain all snow. For
locations along the lee of the Kenai and Chugach Mountains, snow
amounts will be much less due to a strong southeasterly cross-
barrier flow which will allow for downsloping and limit the amount
of moisture available away from the coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Today
through Sunday night)...

Dry, windy, and Arctic air will be the name of the game for today
through Sunday afternoon. Arctic high pressure over the interior
will remain dominant keeping any storm systems well south of the
area namely across the southern Bering and Aleutian Island Chain.
While Arctic air is currently in place, another shot of Arctic
air will be drawn southwestward tonight from the interior that
will act to reinforce the Arctic air that was already in place.

With storm systems moving across the Aleutian Chain and a strong
surface high pressure across the interior of Alaska expect
breezy/windy conditions from now through Sunday. These two will
act in concert to keep a tight pressure gradient across the area.
A closed upper level low will move southwestward Saturday
afternoon through Sunday which will provide the upper level
support to yield slightly stronger winds for Saturday afternoon
through Sunday. Sustained northeasterly winds of 20 to 30 mph are
expected across the Kuskokwim Delta with gusts upwards of 40 mph
especially Saturday afternoon through Sunday. Gusty winds are also
expected across Bristol Bay but winds aren't expected to be as
strong. Expect bitter cold wind chills as well Saturday night to
Sunday as low as 35 below zero.

Then, a fairly strong storm system is expected to move
northwestward from the North Pacific to near Kodiak Island on
Sunday. As a result, this will be the beginning of a pattern
change for the area with increasing cloud cover, warming
temperatures, chances of snow, with the potential for downsloping
on the leeward side of the mountains due to southeasterly flow
aloft.

&&

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

The Bering and Aleutian Islands are expected to remain in a rather
active pattern for the next few days with multiple lows moving
through the area. The first low that is currently near Amchitka
will continue moving westward today while slowly weakening. Some
rain showers are expected around Shemya as a result along with
gale force winds for the western Bering today. Another low is
currently over the North Pacific southeast of Adak. This low will
continue slowly moving northward today sending its front into the
Aleutian Islands while the center remains offshore and south of
the coastal marine zones. Expect gale force winds to develop for
the coastal marine zones this afternoon and continue through
tonight. An Arctic air mass moving off the Alaska Mainland will
traverse across the Bering Saturday into Sunday. As a result,
expect increasing winds due to the pressure gradient between high
pressure over the mainland and low pressure south of the Aleutian
Chain. This will cause widespread gale force winds along to much
of the Bering along with increased wave heights. Heavy freezing
spray will also makes its return especially near the ice edge.

&&

.MARINE (Days 3 through 5 - Sunday through Tuesday)...

Gulf of Alaska: North pacific low moves just south of the AKPen
on Sunday, bringing waves above 20ft and winds greater than 35kts
to much of the Gulf. Winds and waves begin to subside by Monday.

Bering Sea: Northerly flow on the backside of a low near the AKPen
will produce gale force winds across the Bering and Aleutian
Coasts on Sunday before subsiding on Monday. Seas are expected to
remain below 20 ft Sunday through Tuesday, but may approach 20ft
in ares with highest winds on Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Monday through Thursday)...

As we begin the long term the region will be in the midst of a pattern
change. The blocking high that has been over Alaska this week will
shift towards eastern Russia while a broad trough will develop over
the Bering and Aleutians and extend towards southcentral Alaska.
Additionally, a strong ridge will develop over western Canada and
extend into the interior of Alaska. The western Canadian ridge
will direct lows and fronts northward into southcentral with
milder temperatures and moist southerly flow bringing rain and
snow for parts of southcentral. This pattern will also allow a
couple of lows to cross into the Aleutians and Bering from the
North Pacific which could bring periods of strong winds to parts
of the Aleutians and Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 131.
MARINE...Storm 130. Gale 155 170 172 173 174 175 176 351 179 174
175 176 351 179 180 185 411 412 413 414 119 120 125 127 128 131
138 139. Heavy Freezing Spray 165 179 185 119 121 126 127 128 129
130 139.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...RC

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
226 PM AKST Fri Jan 7 2022

AKZ111-081500-
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
226 PM AKST Fri Jan 7 2022

...STRONG WINDS FRIDAY AFTERNOON THROUGH SUNDAY...

Northeast winds sustained 20 to 35 mph, with gusts up to 45 mph,
will return Friday afternoon and continue through the overnight
hours before slowly diminishing Saturday. These winds are then
expected to increase again late Saturday evening and continue
through Sunday before diminishing by Monday morning. Loose debris
may still be affected by these winds and should be secured where
possible.

Wind chills from 10 to 25 below zero are expected with higher
winds. This could cause dangerous life-threatening conditions for
those without power, as frostbite can develop in as little as as
15 minutes in these conditions.

For the latest information, visit us at: weather.gov/anchorage.