Gale Warning 66, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKST Fri Jan 20 2023

.ANALYSIS AND UPPER LEVELS...
Looking at the satellite imagery over the North Pacific and
Alaska, there are three lows that stand out. Two are in the
Bering Sea or south of the Bering and the other is in the Gulf of
Alaska. The Gulf of Alaska storm will impact Southcentral and,
indirectly, Southwest Alaska the next few days. This low has a
very long tap of warm and moist air associated with it as can be
seen on GOES 18 satellite. The warmest and wettest of this air is
heading toward Southeast through the lower clouds over the Gulf
are fairly warm as can be seen on IR. This is contrasted with the
cold air cumulus clouds streaming across the Alaska Peninsula
and into the southwest section of the Gulf low. The cold air is
entrenched over Southwest Alaska which is under high pressure.
This is creating a strong pressure gradient over parts of the
Bering and Southwest Alaska and how the Gulf low is impacting
Southwest Alaska.

The next two lows are farther west with one near Kiska Island and
the other well south of Adak near 40N. The jet stream is feeding
into the more southerly low and strengthen it as it moves
northward toward the Aleutians. The jet max is close to 190 KT at
250 mb so there is a bit of energy to feed this low located in
the favored left front exit region of the jet streak.

&&

.MODEL DISCUSSION...
Models are in good agreement with the synoptic features through
the weekend. Early next week they do start to diverge a bit in
regards to the complex low along the Aleutian and Alaska
Peninsula. This will have some trickle-down effects for mainland
Alaska by mid-week, though there is still usable information to
discern from them. For the shorter term, the high-resolution
models such as HRRR and NamNest continue to outperform the rest of
the bunch with the southeasterly waves across Southcentral
Alaska. The biggest concerns in Southcentral model disparity may
have more to do with freezing levels and how that will translate
to precipitation-type through the weekend along coastal mountains.
The GFS and NAM are doing well for Southwest Alaska and the
Bering Sea region.

&&

.AVIATION...
PANC...Overall, VFR conditions and light winds will persist. There
is a slight chance for some light snow to cause brief MVFR
conditions late tonight or early Saturday morning.

&&

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

A strong low southeast of Middleton Island this afternoon will
slowly weaken and drift onshore near Yakutat tomorrow afternoon.
The system's front is currently over eastern Prince William
Sound and will swing west into Western Prince William Sound
around midnight tonight. Some overrunning moisture may be enough
to give the Anchorage Bowl a light dusting over snow overnight,
but overall moisture content is low. Additional light snow may
linger through the morning hours tomorrow over the Anchorage and
Eagle River Hillsides as flow aloft becomes westerly and upsloping
squeezes out any remaining moisture. The other side to this
system are gap/outflow winds that are ramping up rapidly through
Seward, Whittier, and Thompson Pass, which will remain ovulated
through Saturday afternoon. Skies should clear through the day
tomorrow from west to east, which will allow for some cooler
morning lows to develop on Sunday.

Sunday will begin a pattern change towards a warmer weather regime
as flow aloft shifts to be more southerly to southwesterly. This
will usher in a warmer, wetter airmass with the potential to bring
in some mixed precipitation or rain to non-coastal areas by
Monday as a series of progressively warmer storms move into the
area. Forecast confidence is generally low to moderate on timing
of precipitation and/or precipitation type as we get into the
Monday timeframe. The first of the series of systems will move
into the coast Sunday morning, increasing winds through Turnagain
arm and bringing a transition of snow to rain at sea level through
the evening. With ample cold air pushing into the coast ahead of
this system, snow levels shouldn't rise too high on Sunday, but
will continue to creep up to around 1200 to 1500 ft by Monday,
which could create some difficult travel conditions as rain falls
on snow covered roadways along the Seward and Richardson highways.
Stay tuned for more details as the forecast evolves.

&&

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

An upper-level trough with embedded shortwaves lifts to the
northeast while a strong upper ridge builds in its wake. As a
result, precipitation lingering along the Alaska Peninsula,
Western Alaska Range, and Kuskokwim Mountains will taper off
tonight. Clear skies and cooler temperatures will prevail across
much of Southwest under ridge, with the coldest temperatures
expected across the Kuskokwim Delta. Northerly winds combined with
cold temperatures could create very low wind chills (as low as 45
below zero) across the Kuskokwim Delta, and thus, a Wind Chill
Advisory is in effect from this evening through Saturday morning
for this region. For the rest of Saturday, northeasterly winds
will increase, cloud cover returns, and temperatures trend warmer
in response to a low nearing the Bering Sea. As the low lifts its
front northward, precipitation will return first to the Alaska
Peninsula Saturday night before spreading light and showery
precipitation inland to the Southwest Mainland through Monday.
Strong offshore flow will persist into Monday and may have the
potential to transport already existing snow within the Kuskokwim
Delta and Bristol Bay areas.

&&

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

An active weather pattern continues for the Bering Sea and
Aleutians through the short-term period. A compact low over the
Western and Central Aleutians will continue deepening as it tracks
across the Western Bering tonight. Widespread gales, with
localized storm force winds, and steady precipitation will
accompany the low as it exits towards Russia by Saturday morning.
Its occluded low will linger over the Western Bering as another
(stronger) system approaches from the North Pacific. This second
low will extend its front across the Aleutian Islands beginning
Saturday morning. Easterly winds will start to increase tonight
and then peak mid-afternoon through early evening tomorrow.
Sustained storm-force winds with gusts to hurricane-force are
anticipated across the Eastern Aleutians. Thus, a High Wind
Warning is in effect for the Eastern Aleutians from Saturday
afternoon into Saturday night. Winds will diminish late Saturday
night into Sunday morning as the front weakens. Precipitation with
the front will likely start as snow before transitioning to all
rain by Saturday evening. The strong winds may combine with
initial snowfall to promote a period of low visibilities. As the
front lifts northward and weakens, winds slowly diminish and light
precipitation spreads across much of the Bering through Monday.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

Overall the struggle with a complex pattern evolution, even prior
to the extended timeframe, continues to throw a large wrench into
the gears from a predictability standpoint. The model consensus
for the behavior of an Arctic low situated over far northeastern
Russia and out towards the Bering Strait continues to shift, again
with big changes appearing even in the shorter term on Sunday and
Monday. By the start of the period on Tuesday, models have
partially shifted back to the scenario where the low becomes a
stretched out trough between the North Slope and Norton Sound as
it becomes sandwiched between a blocking high drifting into the
East Siberian Sea and a much stronger ridge extending into
northwest Canada and Southeast Alaska. With the exception of the
ECMWF, most solutions still keep the Arctic air mass to the north
of the Alaska Range, with much more mild conditions still likely
across most of Southwest and Southcentral between Tuesday and at
least Thursday as strong south to southwest flow persists around
the ridge extending over Canada and across much of the Gulf.

Most of the southern Mainland will remain in an active pattern
and right under fire from the prevailing storm track. Several
lows will likely to track into Southcentral through Thursday,
bringing multiple rounds of snow and rain into the region.
Meanwhile, a deep low stalling out near Kamchatka will push a
strong front northeastward across the Bering and Aleutians, likely
remaining gale force or stronger until it approaches the Southwest
coast by Thursday night. There are early indications for the
ridge to amplify and shift west by Friday, perhaps allowing for in
a break in the active pattern towards the end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 131
	 	 Wind Chill Advisory: 155
		 High Wind Warning: 185
MARINE...Storm Warning: 130 155 170-174 176 179
						411 412 413 414
		 Gale Warning: 119 131 132 137 138 150 150 165
					   175 177 178 180 181 185 351 352
	 	 Heavy Freezing Spray Warning: 160 165 179 180 185 412 414
FIRE WEATHER...NONE.

&&

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