Gale Warning 179, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 PM AKST Fri Feb 24 2023

.ANALYSIS AND UPPER LEVELS...

The upper level pattern has become more progressive today as the
trough and ridge have flattened. The jet stream runs west to east
across the area from the Aleutians extending into the southern
Gulf. An low pressure system is moving towards the western
Aleutians with an increase in winds and seas. A shortwave is
transversing across the eastern Bering moving towards the
Kuskokwim Delta. This is producing snow showers across the
Bering, the Pribilof Islands, the eastern Aleutians, and the
AKPen. Another shortwave is moving across Southwest Alaska with
some light snow seen on radar across the Kuskokwim Delta. To the
east a shortwave is pushing east with an occasional snow shower
associated with it, however a surface low over the northern Gulf
continues to produce light snow from Valdez to Cordova and is
moving east which will end the threat of snow for these areas this
afternoon. Otherwise, fog and stratus was reported from the
western Kenai Peninsula and north across Anchorage and the Mat-Su
valleys. Most of the fog has lifted but low stratus continues to
linger across the area.

&&

.MODEL DISCUSSION...

Model are in good agreement through Sunday, but are struggling
with the timing and strength an approaching low pressure system
moving into the Bering on Sunday, and then towards the Southwest
Monday and Tuesday. The main challenges with this system will be
determining precipitation types across the Southwest and timing of
the snow across Southcentral early next week. Otherwise, the near
term challenge will be the threat of fog across parts of the
southern mainland.

&&

.AVIATION...
PANC...Mainly VFR conditions are expected through late evening,
but going into the overnight hours, chances increase that ceilings
and visibility could drop to IFR for a few hours as light snow
moves through the area. VFR conditions are expected by late
tomorrow morning or afternoon as the clouds clear from the area.
There is a low threat of fog tomorrow morning, but cloud cover
should hinder its development.

&&

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

Heading into early next week, an upper level trough moves over
Southcentral, which will increase outflow winds through the usual
gaps and passes over the mainland. Meanwhile, a shortwave may
bring some snow showers through overnight, but most of it will be
in the higher elevations. Over the Gulf waters, gusty north to
northwest winds will strengthen as the pressure gradient increases
and cold air pushes into the area. The strongest winds will happen
between tonight and Saturday, especially from Prince William
Sound to Kodiak Island. Winds are expected to briefly subside
Saturday night before ramping up again on Sunday. Skies will also
clear out with calm winds in the inland areas, allowing
temperatures to drop back down in the single digits to below zero.

&&

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

A shortwave trough traversing Southwest Alaska this evening is
producing light snow showers across the Kuskokwim Delta and Lower
Kuskokwim Valley. Snow showers are expected to continue as the
main focus of activity shifts from the Kuskokwim Delta region
early this evening into the Lower Kuskokwim Valley later tonight
as the shortwave pushes eastward. However, snow accumulations from
this system are expected to be less than an inch. As the snow ends
from west to east tonight, a transient ridge pushes across the
area, bringing drier and clearer conditions which should allow for
some cooler low temperatures tonight, especially over the Lower
Kuskokwim Valley and Bristol Bay, where temperatures will drop
into the teens and single digits.

Then, a Bering low pushes its cold front along the Southwest
coast Saturday morning, though little precipitation is expected
further inland than the western capes as the low elongates and
exits to the southeast across the Alaska Peninsula. A trailing
front associated with a surge of much colder air to the north will
sweep southward across the region and bring another chance of
snow and much colder temperatures. Up to an inch of snow
accumulation will be possible Saturday night, primarily in the
Kuskokwim Delta, as this front tracks south. Temperatures plummet
with northerly cold advection behind the front, dropping
temperatures in the interior below zero, with single digits along
the coastal portions of Bristol Bay. A strengthening anticyclone
in the northern Bering continues to push colder air into Southwest
Alaska through Sunday and Sunday night, while drier air keeps
skies mostly clear. This will allow temperatures to continue to
fall through early Monday morning.

Going into the next week, temperatures should rebound somewhat
with the arrival of another storm system tracking in from the
Bering Sea. However, there is significant uncertainty with the
track and structure of this system at this time. The main thing to
note is that with the warming temperatures, there is significant
potential for a transition to mixed precipitation, with freezing
rain possible before a switch over to rain for some parts of
Southwest Alaska early next week.

&&

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

An active pattern looks to return to the Bering Sea after a brief
respite within a fairly benign, showery regime the past few days.
A deepening low centered just north of Attu Island this afternoon
will track into the central Bering Sea tonight as it strengthens.
Storm force winds develop tonight on the south side of the low,
bolstered by cold air wrapping in behind the low. Further to the
south, westerly gales with rain and snow push along the Aleutian
Chain. The low occludes and begins dipping south on Saturday as it
approaches the Southwest coast. The swath of strongest winds
pushes across the eastern Aleutians, with localized areas of storm
force winds and gusts to 70 mph expected. As the low elongates
and weakens, the corridor of winds shifts eastward over the
southern Alaska Peninsula and weakens in kind Saturday night. At
the same time, another low crosses the western Aleutians on its
way into the Bering. The specifics of this system remain quite
uncertain, but the broad expectation is for a much warmer air mass
to lift out of the North Pacific, bringing rain to the Aleutian
Islands. The low pushes into the central Bering Sea Sunday night,
and it is likely to be associated with an area of gale force winds
wrapping the low, though models currently disagree on how
elongated or consolidated it will be. This has significant
implications on the strength of the winds associated with the
system as well as the track it will take, particularly with
regards to the forward speed. Stay tuned for further updates.

&&

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

Starting Tuesday morning, agreement between the 12Z deterministic
model runs is weak, with stark discrepancies regarding synoptic
features. Namely, a low in the Bering Tuesday morning is
positioned by the GFS in the Central Bering, with a front having
just pushed inland into Southwest Alaska. The Euro model suggests
that the low is positioned slightly more to the south, with the
front just offshore of Southwest Alaska. The Canadian model is
much more progressive and the outlier, positioning the low over
the Southwestern coastline, and the front having already pushed
significantly inland, reaching Southcentral already by Tuesday
morning. These differences erode initial forecast confidence. The
lows then look to push inland, with the GFS showing a slower,
heavier precipitation event for Southwest and Southcentral as the
low makes its way east. By Wednesday morning, the GFS shows a
strong precipitation event for the Greater Bristol Bay area to the
Prince William Sound and Eastern Kenai. Wednesday morning the
Euro advertises the low moving into Prince William Sound just with
significantly less of a precipitation signature. The low
represented by the Canadian model has since departed Southcentral
by Wednesday morning, leaving some remnant showers behind.

Solutions appear to converge more by Wednesday afternoon, as
showers across Southern Alaska dissipate by Thursday morning.
Winds associated with these events do show decent agreement, with
the GFS and Euro solutions suggesting gusty winds through the gaps
and passes of the Eastern Aleutians Wednesday afternoon.
Additionally, as the low moves east, strong winds through the
Barren Islands are currently expected between Thursday morning and
that afternoon. A weak low looks to enter the Western Bering by
late Wednesday night moving across the Chain, exiting to the south
upon reaching the AKPen Thursday afternoon. Southwest and
Southcentral Alaska look to enjoy a reprieve from activity through
late Thursday into Friday evening as high pressure moves to build
in. Friday afternoon, the GFS solution shows a front from a
Kamchatka low approaching Southwest Alaska, however the Euro
solution mostly disregards this front and instead builds a North
Pacific low to approach the southern edge of the Central Aleutians
by Friday afternoon instead. Given time, disagreements between
the solutions will diminish, so stay tuned to our latest forecast
to keep up- to-date on this potentially active pattern next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY 127 129 160 180 181 185 414
STORM 170 171 173 178 413 414
GALE 120 127 130 131 132 138 150
155 160 165 172 174 175 176 177 179 351 352 411 412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...CL