Wind Chill Advisory 1, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified across the North Pacific with upper
level ridging extending across the west coast of the lower-48. A
deep upper level low currently extends across eastern Sibera
through the Seward Peninsula. A negatively tilted trough currently
extends southeastward from the aforementioned low center into the
North Pacific. A second upper level low is currently lingering
over the western Aleutians. A third low is currently developing
along a negatively tilted trough extending from the aforementioned
low over the western Aleutians into the North Pacific. This third
low is currently moving northward.

Closer to the surface, radar imagery shows precipitation moving
northward from the Gulf of Alaska to over Southcentral Alaska.
Observations show precipitation type to be rain along the
immediate coastal areas of the southern Kenai Peninsula and across
Prince William Sound. Snow is the precipitation type across the
Kenai and Chugach Mountains as well as in the Anchorage Bowl.

Radar imagery also shows areas of light snow across the Kuskokwim
Delta and across the northern Alaska Peninsula and in Bristol Bay.

&&

.MODEL DISCUSSION...

Guidance remains in good agreement with respect to the placement
and intensity of synoptic scale features. The biggest forecast
challenge continues to be smaller scale mesoscale features and
local effects. Forecast confidence overall is average.

&&

.AVIATION...
PANC...Conditions will mainly be MVFR to IFR this TAF period as
ceilings and visiblity will both fluctuate. Winds will remain
light during this time.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Today through Sunday night)...

A North Pacific low center with the elongated trough is moving
northward into the Gulf this morning. Easterly waves wrapping
around the low is pushing snow showers across Southcentral last
night through this morning. Northerly winds at the surface for
Anchorage along with this passage has led to a little higher than
expected snow amounts. This is expected to taper off over the next
few hours this morning as the synoptic wind field shifts
easterly, downsloping Anchorage and western Kenai Peninsula, and
finally northerly this afternoon. Cooler air will then advect
across Southcentral. The low track has come into better agreement
with the center moving towards Cape Suckling and Yakutat. There
are still some uncertainties that remain with the timing of each
successive wave and timing of the low tracking more inland and
eastward, especially for Saturday as a ridge begins to build in
from west to east. Widespread gales over the Gulf is likely with
this low. As the low approaches the coast, winds are expected to
increase in the Valdez and Cordova area. Snow falling in Thompson
Pass along with the increased north to northeasterly winds will
lead to reduced visibility and blowing snow. Although overall
accumulations are expected to be about two to four inches, a
Winter Weather Advisory is in effect from noon to 9PM. Winds
appear to remain beyond midnight elevated after snow diminishes.

With a more progressive pattern, the ridge will be brief and
allow temperatures to be cooler this weekend. The next system will
enter the western Gulf late Saturday night into Sunday morning.
Higher end gales and easterly winds are likely through Sunday
across the Gulf. Plenty of moisture and winds will blow into
Kodiak and through the Barren Islands and Kamishak Gap. Another
repeat of unsettled weather and precipitation type challenges
return with the passage of this trough going into next week.

&&

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

An upper-level trough lifting northeast across Southwest Alaska
will continue to produce light snow showers across much of the
region today. Light snow will gradually clear from west to east
by midday, becoming limited to the slopes of the Western Alaska
Range by tonight. A strong upper-level ridge will move in behind
the trough, bringing dry and clear conditions for Southwest Alaska
beginning Friday night. Clear skies will allow temperatures to
fall area-wide, with temperatures approaching 20 below zero in
the Kuskokwim Delta. This will allow wind chills to reach near 40
below zero by early Saturday morning with light northerly flow.
Winds increase on Saturday as the pressure gradient increases in
response to a deep low nearing the Bering Sea, but temperatures
recover somewhat as the winds mix down warmer air from aloft.
Increasing offshore flow will have the potential to transport
already existing snow within the Kuskokwim Delta and Bristol Bay
regions through Sunday even as the area remains otherwise dry.
Then, clouds and precipitation reach the Alaska Peninsula starting
Saturday night as the low pushes its front northward. By Sunday,
the leading edge of the front reaches the Southwest coast,
allowing for the onset of light and showery precipitation.

&&

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

Active weather is forecast to continue for the Bering
Sea/Aleutians through the weekend. First, a weak low south of
Kiska will deepen this morning as it pushes north across the
western Aleutians. This low will develop into a strong, compact
system, bringing gales, with localized storm force winds, to the
western/central Aleutians today. Snow may briefly be possible
before changing over to rain by midday. The low then moves into
the western Bering Sea tonight as it continues to deepen, exiting
toward Russia by Saturday morning.

Then, a second low in the North Pacific, located several hundred
miles south of Adak this morning, will push a front across the
Aleutian Islands beginning Saturday morning. This low will prove
more impactful as it begins to run up against strong surface
ridging in the northern Bering Sea, driving storm force easterly
winds through the eastern Aleutians on Saturday. Steep low-level
lapse rates will be present in an environment with 90 mph winds
in the low levels of the atmosphere, suggesting a significant
potential for hurricane force gusts to mix down to the surface as
the front pushes through. This has prompted the issuance of a High
Wind Watch for the eastern Aleutians, including Dutch Harbor and
Nikolski, which may see gusts as high as 80 mph. As the peak of
the winds ends Saturday evening with the front pushing northward,
snow will begin for the Aleutian Chain before transitioning to
rain later Saturday night. Strong, gusty winds also move into the
Pribilof Islands within a similar environment Saturday afternoon
and evening as the low tracks northward. However, hurricane force
gusts appear less likely there at this time. Gale force winds
with air temperatures in the single digits driving off the ice
cover will also induce the potential for extreme freezing spray
near the ice edge.

By Sunday, the low begins to occlude, allowing for the strongest
winds to diminish along the front. Though, strong surface high
pressure will persist in the Chukchi Sea, continuing to support a
strong pressure gradient across the Bering. As a result, storm
force winds stick around into Sunday as the front pushes into the
northern Bering.

&&
.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

The overall pattern in the extended range continues to be
difficult to resolve, with even some of the larger scale players
in the pattern evolution shifting around considerably in terms of
the run-to-run continuity. One of the biggest changes is that
newer model runs from today are no longer showing the Arctic low
currently drifting near Siberia move nearly as far south as it
heads east towards northern Alaska over the weekend, resulting in
a very different looking setup across the Bering and Southwest at
the start of the extended period on Monday. Most solutions now
keep the low and most of the bitterly cold Arctic air well removed
from the outlook area over the Interior and North Slope, with the
projections showing the low stretch out to the south and allow
very cold air to spread into the eastern Bering and Southwest
losing support. The lack of cold, dense air and higher pressure
developing across the same region has resulted in big shifts for
the track of a large area of low pressure expected to move past
the Aleutians into the southern Bering early next week. The
consensus from 12z guidance has shifted the low track
significantly north, now showing the low and a deep upper trough
lift well into the Bering on Monday and Tuesday rather than
staying along or south of the Aleutian Chain.

The potential for precipitation east of the low extending across
Southwest and Southcentral has shifted notably north as well, with
much higher potential for interior parts of the southern Mainland
to see periods of snow or even rain as deep, southerly flow
pushes warm air and multiple shortwaves inland from the Gulf
through midweek. All of the large, wild shifts in even the broader
scale pattern make it nearly impossible to hash out details for
individual systems, but it does look like a clear tilt towards a
warmer/wetter period for much of next week. There is also an
emerging signal for a very potent low to enter the far western
Bering by Thursday, possibly impacting the western fringes of the
Aleutians/Bering with storm force winds, and perhaps even
stronger. The GFS is by far the most bullish with this scenario,
currently depicting a 930-940 mb Hurricane force low move west of
Attu by Thursday afternoon. The ECMWF/Canadian are much weaker
with this system and are showing the low move much farther west.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 185.
Winter Weather Advisory 131.
MARINE...Heavy Freezing Spray Warning 160 165 179 180 185 412 414.
Storm Warning 130 170 171 172 173 174 176 177 411 412 413 414.
Gale Warning 119 131 132 138 150 155 160 165 175 178 179 180 185 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...AS