Gale Warning 153, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 PM AKST Sun Feb 6 2022

.ANALYSIS AND UPPER LEVELS...

In the upper levels, a series of jet streaks are supporting a low
that is slowing down over the northern Gulf. The right entrance
region of a jet streak over the Interior is working with the left
exit region of a separate jet streak over the Panhandle.
Unfortunately for the low, both of those jet supports are quickly
leaving the low behind to the east. Meanwhile, a positively-tilted
upper level trough is amplifying southwestward from northern
Alaska down into the northern Bering and Southwest Alaska. This
feature developing a cutoff low will be the main support for the
very active weather across Southcentral this upcoming workweek.
The low over the Gulf is producing a solid area of heavy rain
over the northern Gulf impacting Cordova, while a 34 degree snow
is falling over Valdez.

&&

.MODEL DISCUSSION...

The models are in decent agreement through Tuesday afternoon. They
are finally locking into the storm track for the next several
lows, taking the surface lows near or over Kodiak Island and then
near or over the Kenai Peninsula after that. Along this track,
Prince William Sound will stay on the warm side of things, with
some variability (though mostly warm temperatures) across the Cook
Inlet region. Cooler air will race in behind each low, only to be
replaced soon thereafter with the warm air leading ahead of the
subsequent low. Meanwhile the forecast across Southwest Alaska has
been solid for days with very cold conditions for the Kuskokwim
Delta, where a Wind Chill Advisory remains in effect. There is
significant uncertainty as to the wrap-around precipitation west
of the low track across eastern portions of Bristol Bay and the
Kuskokwim Valley. The NAM is the typical dry outlier compared
with the other models. Given the cold conditions that will be
present in those areas (though not nearly as cold as the Kuskokwim
Delta), potential for significant amounts of dry powdery snow are
present.

The models are struggling with the speed of the third low
developing well south of the AKPEN Tuesday afternoon, with the GFS
the slowest and the CMC the fastest. Forecast confidence is
average.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist into this
evening. Light snow will develop by about mid-evening and persist
through the night, ending during the Monday morning commute. MVFR
will be the dominant condition during this round of snow, which is
expected to produce around an inch of new accumulation. As usual,
any potential bands of heavier snow will reduce visibilities to
IFR at times. After a pause with VFR conditions returning much of
the day, another round of snow is likely again late Monday
afternoon for the evening commute, in advance of the next in a
series of areas of low pressure systems that will bring a variety
of conditions to the area through the upcoming workweek.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3 -
Tonight through Wednesday)...

The surface low that has been centered just south of Cordova today
has begun to move closer to the coast and should move ashore later
this evening. As it does so the precipitation associated with it
will begin to wane over the Copper River Basin and eastern Prince
William Sound tonight. Meanwhile, two shortwaves in tow will try
to eke out a bit of snow from remnant mid-level moisture wrapping
around the northwest side of the low. The first shortwave will
cross from the southern Kenai this evening to the Copper Basin
early Monday morning. As it passes overhead, it will help to
bring Arctic air into Southcentral and produce light snow from the
western Kenai to Anchorage and the Mat-Su, with southwesterly
low-level flow squeezing out moisture along the western slopes of
the mountains. Accumulation will generally be light, with around
an inch of snow for much of this area. Models are however hinting
at the development of a meso-low, which may result in localized
heavier snow bands on the north and east side of wherever such a
feature sets up. A second shortwave enters the area Monday
morning in time to enhance snowfall over the Susitna Valley, as
low-level flow turns southerly, but is unlikely to do much more
than prolong flurries tapering off further south. Precipitation
will diminish across Southcentral through the day on Monday, but
won't completely end as cyclonic flow aloft and low-level
southerly flow maintain light snow along the southern slopes of
mountain ranges.

A second storm system makes its way up from the Pacific on
Monday as well, tracking near Kodiak Island to the Kenai
Peninsula and then inland. This will bring a batch of warmer air
to the Kenai and Prince William Sound regions, leading to mostly
rain near sea level Monday night into Tuesday. However, ample cold
air over Southwest Alaska will wrap around the south side of the
low and help transition precipitation back to mostly snow. Anchorage
and the Mat Valley are not likely to see much accumulation with
this storm Monday evening through Monday night with plenty of
cross-barrier flow to result in downslope drying. However, this
relaxes Tuesday morning, when there could be a quick shot of
light snow on the back side of the low. With deep southerly flow
behind the low and a fast moving strong short-wave aloft, this
looks favorable for a period of heavy precipitation across Prince
William Sound as well as for the Susitna Valley. The Susitna
Valley should remain cold enough for all snow, with 6 inches or
more of snow likely.

Looking beyond Tuesday, a third storm system looks to take a
similar track to the previous one. Though much uncertainty clouds
the details of this system, it looks to be stronger and warmer
than the previous one. As a result, precipitation type is
somewhat uncertain, with the possibility for rain to begin to mix
in for the western Kenai or potentially the Anchorage Bowl if the
low center tracks to the western side of the Kenai Mountains. A
colder solution for the Cook Inlet region would be in store if it
instead tracks to the east, keeping the bulk of the warmer air over
the western Gulf.

&&

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

Most of the active weather will remain over the southeastern parts
of the outlook area over the next several days as a train of low
pressure systems moves up from the North Pacific toward Kodiak
Island and into Southcentral. Farther west, frigid, Arctic air
will dominate the pattern through midweek, with temperatures
expected to plummet to as cold as -25F over parts of the the
Kuskokwim Delta by early tomorrow Morning and again on Tuesday
morning. A Wind Chill Advisory will go into effect this evening
for the Kuskokwim Delta due to expected wind chills dropping as
low as -50F at times with gusty northerly winds persisting as
temperatures drop.

Looking at the details for the aforementioned train of lows, it
now looks likely two main system will bring two separate bands of
light to moderate snowfall across mainly the eastern half of
Bristol Bay and up across the Middle Kuskokwim Valley. The first
round of snow will begin by tomorrow evening along a strongly
baroclinic zone (a sharp temperature and pressure gradient)
developing between a low moving over Kodiak Island and the cold
Arctic air anchored under a polar low drifting over the Kuskokwim
Delta. Both the upper level support and the developing snow band
and the surface low to the southeast will advance rapidly north
tomorrow night, yielding a brief but intense period of snowfall
developing near or just east of King Salmon and shifting north
into Iliamna and Sleetmute through Tuesday morning. New snowfall
accumulation of 2 to 4 inches is expected for the areas mentioned
above for this first round of snow, with locally as high as 6
inches remaining possible.

A brief break in the snow for the areas impacted is expected by
late Tuesday morning, before the next low in the train takes a
very similar track across Kodiak Island and then northeast into
Southcentral late on Tuesday into Wednesday morning. The overall
setup should play out in a similar manner as well over Bristol Bay
and the Middle Kuskokwim Valley, with another band of snow
developing Tuesday night and shifting a bit more slowly north
through Wednesday. This low and subsequent snow band development
should be a bit more potent than the first system, with snowfall
ranging from 2 to 6 inches of new snow expected along and west of
an axis from King Salmon to Sleetmute through midday Wednesday.

Some uncertainty remains for timing and snowfall amounts for both
rounds of snowfall expected over the eastern portions of the
outlook area, so be sure to check back for additional forecast
adjustments.

&&

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

A blast of Arctic air will spread south and west across the
entire Bering Sea through midweek as a polar upper low drifts out
into the eastern Bering from Southwest Alaska. Persistent and
nearly steady northeasterly winds between 20 and 30 kts will
continue to advect frigidly cold air into the entire region, with
potential for the Pribilofs to see temperatures dip down to
around 0F for both Tuesday and Wednesday morning. Seasonably cold
temperatures in the 10s and 20s are on tap across the Aleutian
Chain as well through at least Wednesday. Heavy freezing spray
will become an increasingly widespread concern with these very
cold temperatures and persistent northeast winds, with areas
between the southern Alaska Peninsula, Pribilofs, and much of the
open Bering under threat for heavy freezing spray rates. Snow
showers will become widespread over the next several days as well,
with areas of blowing snow also possible across the Aleutians and
Pribilofs with the brisk northeast winds.

&&

.Marine (Days 3 through 5: Wednesday through Friday)...

Gulf of Alaska:

A mature North Pacific low with an associated front will move
towards the Gulf late Tuesday night and Wednesday. This low will
produce a widespread area of gale force winds through Thursday.
The actual surface low will move inland early Thursday but the
tight pressure gradient will remain over the northern Gulf. The
models bring another Pacific low into the Gulf on Friday expect
another round of gale force winds.

Bering Sea/Aleutians:

The ice shield will continue to grow as arctic air gets advected
into the Northern and Central Bering. Just south of this ice
shield expect freezing spray and possibly heavy freezing spray.
With the thermal gradients in place, expect northwesterly gale
force winds funneling through gaps and passes along the Central
and Eastern Aleutians/Alaska Peninsula through Thursday
afternoon. Another North Pacific low will approach near the
Central Aleutians Thursday morning. There is a potential for
another round of gales and enhanced in associated with this low.
There is model uncertainty with the overall track, position, and
strength associated with this storm system. Therefore, forecast
will be updated and fine tuned as better model data becomes
available.

&&

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

The models all show an active and wet period for the North
Pacific and the persistence of the longwave trough over the Bering
and the Northwest Pacific. The models show 3 distinct lows for
this forecast period. However, there is substantial divergence
with the tracks and the intensities of these lows. Expect an
active weather pattern for the entire southern state as a series
of North Pacific lows dominate the region. Additionally, the
models show persistence with the brutally cold air over the
northern Bering and over most of the state. However, these Pacific
lows will bring relatively warmer air with them and places like
Prince William Sound could see rain and snow.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory...155.
MARINE...Gales: 119, 120, 130, 131, 138, 139, 185, 352.
         Heavy Freezing Spray: 150, 155, 160, 165, 179, 185, 411, 412, 413, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...PJS