Gale Warning 59, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 PM AKST Wed Jan 18 2023

.ANALYSIS AND UPPER LEVELS...

In the upper levels a deepening trough extends south of the
Aleutians with a ridge across the southern Gulf. The jet stream
runs from the north Pacific well south of the Aleutians and then
bends northeastward towards the Gulf and then dives southeast into
the eastern Gulf. A strong low pressure system south of Unalaska
is pushing a front towards the southern Gulf with gale force winds
ahead of the front. Across the Bering weather is fairly benign
with a broad upper level ridge, northerly surface flow less than
25 knots, and areas of light rain and snow. Across Southwest
Alaska a surface trough is producing light snow across the
Kuskokwim Delta.

Across Southcentral an upper level shortwave trough is pushing
north across the Kenai Peninsula producing light snow from Homer
and northward to Soldotna. A vertically stacked low is spinning
just to the east of Middleton Island and slowly moving north.
This low is producing light rain and snow across portions of
Prince William Sound with Whittier and Portage reporting snow with
temperatures hovering around 32 degrees. Otherwise from Anchorage
and north and east the area is dry with mainly mid and high level
clouds. Dense fog was reported around the Anchorage area this
morning, but dissipated by mid- day.

&&

.MODEL DISCUSSION...

Forecast confidence is good through Friday with models handling
the large scale synoptic pattern fairly well. There continues to
be some small disagreements with a stronger low moving northward
through the eastern Gulf Friday with models bringing it onshore
anywhere between Cordova and Yakutat. The biggest forecast
challenge will be timing any precipitation that spills over the
lee side of the mountains bringing light snow inland.

&&

.AVIATION...
PANC...VFR conditions are expected most of the TAF period. However
there is a chance of MVFR or IFR ceilings and visibility through
the late evening hours as an upper level shortwave brings light
snow near the terminal. The character of the snow looks showery,
so would expect up and down conditions as bands of snow move
through.

&&

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

A surface low located near Middleton Island, as seen on Satellite
Imagery this afternoon, will transition to an elongated trough
over the northern Gulf. This feature, along with an upper-level
shortwave tracking up Cook Inlet, will likely develop a band of
snow and track northward towards Anchorage this evening into
tonight. Accumulations with this band will be relatively light
with only a coating to around an inch or so of snow expected.
This feature has also been causing the light snow shown on radar
for the eastern Kenai Peninsula to Cordova. Easterly gale-force
winds will develop across the southern Gulf tonight and move north
through Thursday. As easterly winds eventually work their way
into Whittier and eastern Turnagain Arm, this will bring warmer
air into these areas and change precipitation from snow to rain by
early Friday morning. Models have been struggling with the
orientation of the surface front tracking into the region, which
impacts when the warmer air will push into the aforementioned
areas. If the front continues to be resolved by models as having a
northeast/southwest orientation, then snow will stick around until
Friday morning, but if it changes orientation and brings those
gusty easterly winds in sooner, warmer air could push in and
change snow to rain sooner than currently forecasted. The surface
low associated with the front will stall near Kodiak Thursday
with another upper-level wave moving north over the Gulf. This
wave will help maintain the south-southeasterly flow and moisture
advection aloft and keep widespread precipitation along the coast
through the end of the work week. Heading into the weekend, a
North Pacific low will track into the eastern Gulf and bring
stronger winds an precipitation to the region. Models are having
a hard time with the finer details of this system, so be sure to
check back for updates to the forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Saturday)...

Light snow showers will taper off across the Southwest Mainland
this evening as a trough exits to the north. A front extending
from a North Pacific low is currently grazing the southern side of
the Eastern Aleutians and Alaska Peninsula and will lift to the
north Gulf coast by Thursday morning. The low itself will track
south of the Alaska Peninsula (near Kodiak Island) also on
Thursday morning and will remain nearly stationary through Friday
morning, at which time it gets absorbed by another low in the
Gulf. That being said, expect snow to begin along the Alaska
Peninsula later Thursday morning. Light snow showers could spread
to the Bristol Bay, Kuskokwim Delta, and Lower Kuskokwim Valley
later Thursday into Friday as upper shortwaves traverse the
regions. However, the heaviest snow amounts are expected to remain
along the Alaska Peninsula near Pilot Point/Port Heiden from
Thursday afternoon through Friday morning. On Saturday, snow will
taper off and skies will clear from west to east across Southwest
as the Gulf low exits to the east and an upper ridge builds in
from the Bering.

In terms of wind, strong northerly cold air advection along the
backside of the Gulf low will promote elevated winds across the
Kuskokwim Delta, Bristol Bay, and Alaska Peninsula through most
of the short term forecast period. Northerly winds will become
especially gusty through the gaps and passes of the Alaska
Peninsula from Friday afternoon through Saturday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3: Tonight
through Saturday)...

A low near the Kamchatka Peninsula currently extends its front
across the Western Bering and Central Aleutians while a weak
surface trough spreads light snow across the rest of the Bering.
The front will gradually track east and weaken over the Western
and Southern Bering on Friday morning. Also on Friday morning, a
compact North Pacific low will approach the Western/Central
Aleutians and then exit the Western Bering towards Russia on
Saturday morning, with its front lingering over the Western
Bering. With this system, expect rain and widespread gale-force
winds, with swaths of storm-force possible over the Western
Bering, from Friday afternoon through Saturday for much of the
central and western portions of the domain. A second North
Pacific low (this one looking stronger than the first) is
advertised to lift north to the Aleutian chain sometime on
Saturday. Models are struggling with the timing of this feature.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

An active pattern remains likely for the first half of the coming
week, but most of the details are getting lost in the complex
interaction between a handful of key features that continues to
prove a struggle for models. By the start of the period on
Sunday, models are all showing that a polar low harboring frigid,
Arctic air over Siberia will become displaced by a ridge
developing over the Bering in the short term, resulting in the low
and it's associated Arctic air moving west into the Interior and
North Slope by the end of the weekend. Another large, synoptic low
will be approaching the eastern Aleutians and Alaska Peninsula
from the south by Sunday as well. The resulting pressure gradient
between the low and strong ridge over the northern Bering will
drive a broad swath of northeasterly gale force winds across an
impressive chunk of the Bering Sea, with sustained gales likely
persisting into Monday. An deep frontal zone will extend into the
Gulf east of the center, with a new low likely to form at the
front's triple point somewhere south of the Kenai Peninsula or
Kodiak Island by Sunday evening. Heavy precipitation will spread
into the northern Gulf Coast and Prince William Sound region along
and ahead of this front as a surge of moisture and lift spreads
north through Monday.

From late Monday onwards, the overall outlook becomes increasingly
blurry, with models diverging markedly with the handling of the
Arctic low/trough over northern Alaska. The most recent suite of
operational model runs is showing the low becoming squeezed
between the blocking high over the Bering and another upper ridge
extending into northwestern Canada along a northeast to southwest
axis. Depending on how far the trough becomes stretched to the
south, very cold air could spill down into Southwest Alaska between
Monday and Tuesday, perhaps lingering into Wednesday or later. A
large baroclinic zone will set up to the south across the Gulf and
into Southcentral, with much warmer, moist and southwesterly flow
continuing to push northeast around the upstream ridge. This
should favor continued moderate to heavy snow and coastal rain
across much of the Prince William Sound region, perhaps extending
farther north at times into Southcentral and Bristol Bay. The more
northward extent of snowfall will depend on exactly where the
clash between the Arctic air spilling into the Bering/Southwest
and warmer, maritime air over the Gulf sets up, which remains
highly uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 160 179 180 185.
       Gale Warning 119 120 130 131 138 139 150 155 172 176 177.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...NS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
LONG TERM...AS