Heavy Freezing Spray Warning 184, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 AM AKST Wed Nov 24 2021

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified across the North Pacific as an upper
level trough extends across the Alaskan mainland and upper level
ridging extends across the western Bering/Aleutians. This large
upper level trough is responsible for the unseasonably cold
temperatures across the Alaskan mainland. Satellite imagery shows
widespread convective ocean-effect snow bands across the Bering
Sea as a result of strong cold air advection over the water.
Closer to the surface, radar imagery shows a band of moderate to
heavy snow lingering over the northern Gulf near Middleton Island
moving northwestward into Prince William Sound.

&&

.MODEL DISCUSSION...

Guidance is in good agreement with the placement and intensity of
synoptic scale features at both the surface and in the upper
levels. The biggest area of uncertainty is guidance resolving the
smaller scale features such as where exactly convective snowbands
will set up and move to. With respect to total forecast
confidence, there is high confidence with respect to the general
weather pattern but moderate confidence at best with respect to
fine tuning the smaller scale features.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 2:
Wednesday through Friday)...

An upper-level low currently anchored over Southwest Alaska and
poised to slowly drift east will keep conditions unsettled
through midweek as a series of shortwaves rotate around this
feature. As these waves move from the western Gulf to the
northern Gulf and eventually back over Cook Inlet, they will spin
up compact surface lows, driving them into Prince William Sound.

The first of the surface lows is nearing the eastern Kenai
Peninsula this morning with a plume of moisture streaming up from
the Gulf into Prince William Sound and Portage Valley. Snow,
moderate to heavy at times, is falling again for Whittier and
Portage this morning with some of the moisture beginning to spill
over the mountains toward Cook Inlet. Flurries or very light snow
is expected to develop for Anchorage and Kenai this morning with
more widespread light snow by the afternoon hours. Light snow is
expected to linger for these locations through Wednesday evening
before tapering off as the low now near Whittier weakens in tandem
with the first upper-level wave moving back toward the parent
upper-level low.

A second wave will then lift north from Kodiak Island, moving
over the Kenai Peninsula by early Thursday morning as the upper-
level low begins to shift east. This wave will spin up a new
surface low south of Seward and drive it into western Prince
William Sound. Again, the south-southeasterly fetch ahead of these
features will push another slug of moisture toward Whittier and
Portage Valley. A weak front associated with the low will also
lift toward Cordova and Valdez, with snow also expected for these
locations for Thursday. With the upper-level low over Cook Inlet,
the shortwave rotating around it, and a moist, southeasterly flow
ahead of the surface and mid-level trough, light snow is expected
to persist across the Anchorage Bowl, western Kenai Peninsula, and
Prince William Sound coast through Thursday. The highest snowfall
amounts will be along the coast, especially for Whittier, where
another foot or more could fall between this morning and Thursday.
A couple of inches of snow are possible from Anchorage to Homer
for Thursday.

As the upper-level low begins to shift east, winds in its wake
developing northwesterly winds will advect the arctic air that has
been bottled up over Southwest Alaska through the gaps and passes
of the Alaska Range. Storm-force winds with hurricane-force gusts
are possible through Kamishak Gap to the Barren Islands and
Shelikof Strait for Thursday. Some guidance is also hinting at the
development of a lee-side low over Cook Inlet Thursday in response
to the cold air advection. If this does happen, the cold air out
of Kamishak Gap could be drawn toward Kachemak Bay and the Homer
Bluffs as snow over southern Cook Inlet wraps around the back side
of the low. This could bring locally heavy snow showers and gusty
winds to the southern Kenai Peninsula, especially from Ninilchik
south to Homer and Seldovia for Thanksgiving. Snow showers are
likely to linger across Prince William Sound and the southern Cook
Inlet through Friday as the upper-level low drifts slowly
northeastward over interior Southcentral. Temperatures will
continue their downward as well through the end of the week a
persistent northwesterly flow ushers in much colder air across
Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today through
Thursday night)...

Arctic air will continue to be the main story for Southwest over
the next few days. An upper level low continues to spin in the
vicinity of the western Alaska Range to Kamishak Gap and the
Barren Islands area. As a result, this low will aid in pulling
Arctic air from the Alaska Interior southward into Southwest for
the next two days. Temperatures at 850 mb today will generally be
between -15 to -25 degrees Celsius. Then starting tonight even
colder air will be pulled southward over Southwest with core of
this cold banged up against the Alaska Range. The air coming down
tonight will be between -20 to -30 degrees Celsius at 850 mb with
even some -35 degree Celsius air aloft. Therefore, expect
temperatures today and Thursday to be in the single digits below
zero across interior areas with single numbers for the immediate
coastal locations. Overnight lows will be generally in the
negative teens to 20s below zero with some 30 degrees below zero
especially where the sky is clear and wind is light and variable
or calm.

As this Arctic air moves out over the Bering, it will pick up
moisture as it moves towards the Alaska Peninsula keeping snow
showers and breezy conditions in the forecast for the next two
days. Several inches of snow remain expected where snow showers
remain the most persistent. Also, falling snow combined with the
wind will limit visibility to as low as one half mile at times.
Expect gusty winds upwards of 50 mph through the typical gaps and
passes as well as heavy freezing spray south of the Alaska
Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2:
Today through Thursday night)...

Arctic air remains in place over much of the Bering for the next
two days. As a result, this will lead to unstable conditions over
much of the Bering and cause occasional snow showers for the
Pribilofs and Eastern Aleutians. The Central and Western
Aleutians may also get in on some of the action but it is expected
to be fewer and far between for places such as Adak and Shemya.
Any snow showers will be capable of lowering visibility. Breezy
conditions are also expected to continue for the area through
Thursday evening. As a result of this Arctic air moving out over
the Bering, there will be heavy freezing spray especially near the
ice edge for any marine interests in the area.

A low pressure system will be spinning to the south of the Western
Aleutians tonight through Thursday. Right now, only expecting
small craft winds for the marine waters south of the Chain
Thursday afternoon through Thursday night.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska...On Friday, a digging trough will push cold,
Arctic air offshore, driving strong winds out of gaps along the
Gulf coast and contributing to the formation of a low in the
northern Gulf. These gap winds will have the potential to reach
Small Craft Advisory to potentially Gale Warning levels and
produce heavy freezing spray, especially in the vicinity of
Kamishak Bay and the Barren Islands.

Aleutians/Bering...The North Pacific is active. There is a high
over Siberia and the northern Bering. Localized areas of gales are
possible near the center of a low in the western Bering/Aleutians
on Friday as a front pushes northward.

&&

.Long Term Discussion (Days 4 through 7)...

More Arctic air is headed to Southcentral. Confidence is high
that brutally cold temperatures will return to the region. Cold
air advection will also enhance gap winds. The longwave trough
will remain steadfast over mainland Alaska and negative height
anomalies at 500 mb are expected through Day 7 over Southcentral
and the Gulf Of Alaska. Whereas, positive height anomalies will
remain over the northern Bering. The GFS actually has the cold
anomalies over Southcentral through Day 10.

Out west, a high amplitude ridge persists over the eastern Bering,
keeping the storm track in the western and central Bering through
at least Monday. Models tend to break down this ridge over the
weekend as a result of the second digging trough, with the GFS and
EC bringing colder air streaming over the Bering from the Alaska
mainland.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 130 131 132 137 139 140 141 150 160 165
180 181 414.
Storm Warning 130.
Gale Warning 119 131 132 138 150 155 165 352.
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1012 AM AKST Wed Nov 24 2021

AKZ181-185-195-251500-
Alaska Peninsula-Eastern Aleutians-Pribilof Islands-
Including the cities of Cold Bay, Sand Point, Unalaska, Nikolski,
and Saint Paul
1012 AM AKST Wed Nov 24 2021

...OCCASIONALLY HEAVY SNOW SHOWERS AND STRONG GUSTY WINDS ACROSS
THE EASTERN BERING THROUGH THURSDAY NIGHT...

Snow showers and gusty northwerly winds are expected to continue
across the Alaska Peninsula, Pribilofs, and Eastern Aleutians
through Thursday night. Arctic air continues to move off the
Alaska mainland and over the relatively warm water of the Bering.
Thus, the atmosphere will continue to be moistened and contribute
to snow shower development over the next couple of days. The
pattern is expected to remain stagnant through Thursday night.

Wind gusts ranging from 35 to 55 mph will accompany the snow
showers in these same areas through Thursday night. Snow showers
could be heavy at times within these bands and produce several
inches of snow, especially if these snow showers persistently move
over the same locations. Visibilities could also be reduced to as
low as one half mile at times due to the combination of snow
falling and gusty winds. Locations that may be impacted by these
adverse conditions include False Pass, Port Heiden, Dutch Harbor,
and Saint Paul.