Winter Storm in Alaska, November 22 to 23, 2021

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 PM AKST Mon Nov 22 2021

.ANALYSIS AND UPPER LEVELS...

A persistent upper level low resides over the central part of the
state this afternoon. Mid level moisture is wrapping in from
Canada around this low, bringing mid level clouds across SE and SC
Alaska. At the surface, a meso low is spinning in the northern
Gulf of Alaska, just south of Montague Island. Clouds and snow
showers continue to rotate around this low as it edges north. Snow
is being reported from Cordova to Valdez across Prince William
Sound and through Whittier. Across the Bering, high pressure
continues to get pinched off as a north Pacific low approaches the
central Aleutians.

&&

.MODEL DISCUSSION...

In the short term - models struggled with initializing the meso
low in the Gulf of Alaska. By normal standards, the models did
capture the present state decently and have good agreement moving
into the mid range. By tomorrow afternoon, another low will
develop in the central Gulf of Alaska, though closer to Juneau.
Guidance remains locked with moving this low towards Yakutat and
into Prince William Sound by Wednesday - repeating much of how the
present low will move into the sound.

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through the TAF package. Light snow continuing overnight may cause
cigs and vis to lower near MVFR conditions.

&&

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

A compact surface low near Montague Island, in combination with
an upper level over Southcentral, is currently bringing convective
snow showers across Prince William Sound and through Turnagain
Arm into the Anchorage area. About 0.5 to 1.5 inches of snow is
expected in Anchorage overnight, with locally higher amounts on
the Hillside. Girdwood could see 4-6 inches of snow, while
Whittier could see around 10 inches overnight. Snowfall amounts
are uncertain as models have been struggling with the location of
the compact surface low, and the flow of moisture through
Turnagain Arm and up towards Anchorage. Valdez and Thompson Pass
may see some snow showers overnight as well, though the northerly
extend of the showers remains uncertain. In addition to snow,
outflow winds through the Barren Islands, Resurrection Bay,
Passage Canal, and the Valdez marine zones will continue through
the night as cold air drains out of the interior. In Whittier,
high winds in combination with falling snow will likely lead to
reduced visibilities.

Tuesday will bring a brief lull as the compact low weakens and
outflow winds subside. Snow remains likely in the Prince William
Sound throughout the day. Early Wednesday morning, a complex,
elongated low enters the eastern Gulf and moves north towards
Yakutat. The introduction of warmer air to the east should allow
for a new baroclinic zone to redevelop a low south of Prince
William Sound as it interacts with the polar airmass to the west.
The general pattern supports a return of outflow winds and
snowfall along the Gulf Coast and coastal mountain ranges through
Thursday afternoon.

&&

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

An Arctic low, which is embedded within an upper level trough, is
currently located over Southcentral and proceeds to move along
the Alaska Range. Cold air temperatures continue to be the main
issue associated with this system as the upper level low ushers in
Arctic air from the Alaska interior over most of the state. Highs
will slowly drop through the week with daytime temperatures only
reaching between -15F and 0F. Cold, breezy, and dry conditions are
expected across most of the Southwest and Alaska Peninsula as the
Arctic low tracks toward the Peninsula and northerly flow and
cold advection continues. Some mid and high clouds will continue
to move into the area from the Interior through the period. This
may slightly increase temperatures for some areas as radiational
cooling effects decrease.

&&

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

A North Pacific low and its occluded front are currently located
just south of the Aleutian Chain, particularly the Central
Aleutians. Windy conditions continue to be the main issue
associated with this low as the front maintains easterly winds
(mostly gale force) across the Central Aleutians, with storm force
gusts for the marine water south of the Central Aleutians. Winds
will diminish to below gale force by Tuesday afternoon as the
North Pacific low tracks southeast away from the forecast area.
This system's precipitation is expected to remain south of the
Aleutians and isn't a major forecast concern for the Aleutians or
Bering Sea. High pressure over most of the Bering and Eastern
Aleutians continues to provide relatively benign weather
conditions for those areas. Cold Arctic air moving over the warm
Bering sea surface is creating widespread snow showers which are
impacting the Pribilof Islands at times. This frigid air, combined
with strong northeast winds, facilitates heavy freezing spray
development for the Southwest Coast and Eastern Bering through
Thursday.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska: Multiple weak lows will work north and towards
Prince William Sound through Friday. None of these storms will be
overly strong and only small craft level winds with the occasional
gale force gust would be expected. Similar winds are expected to
traverse Cook Inlet before turning towards the Gulf. Confidence is
high that only low end gales gusts will be expected.

Bering Sea: Winds will follow the peripheries of the ridge
through the end of the week. On the eastern side of the ridge,
northerly small craft winds are expected, with pockets of gale
force gusts stretching east of St Paul southward, through Dutch
Harbor. Across the western axis of the ridge, only small craft
winds will span the western Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Trends across southcentral will be turning back to cold. The
'warmer' conditions that encompassed the region early in the work
week will again turn to well below normal for this time of year.
Snowfall towards the end of the week is not anticipated and
daytime highs across much of the Anchorage Bowl will struggle to
pass zero, while overnight lows will deep to levels that were seen
last weekend. Overall - the synoptic pattern looks to remain
unchanged through next weekend with an anchor upper level low over
the state and weak surface lows spinning into the Gulf of Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 127 130-132 138 173-177
		 Heavy Freezing Spray: 127 130 137-140 150 160 180 181 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHCENTRAL ALASKA...CJ/KC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
MARINE/LONG TERM...MK/SS