Brisk Wind Advisory 78, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Thu Apr 7 2022

.ANALYSIS AND UPPER LEVELS...

A long-wave trough encompasses most of the Alaska Region, anchored
by a deep upper level closed low centered near the Bering Strait.
A strong short-wave trough is rotating around the south side of
this low, pushing onshore across western Alaska. The low level air
mass accompanying this trough is quite cold, with 850 mb
temperatures ranging from -20 to -30 degrees Celsius. With clear
skies across the Kuskokwim Delta, temperatures bottomed out around
zero degrees Fahrenheit. Out ahead of the trough, there is a band
of light snow from the Kuskokwim Valley southward to Bristol Bay,
tracking eastward toward the Alaska Range. A weaker, lower
amplitude short-wave extends from Bristol Bay to south of Kodiak
Island, contributing to snow in Bristol Bay and snow showers
across the western Gulf. Farther east, a deep vertically stacked
low over the eastern Gulf of Alaska is being pulled toward the
northwest as the aforementioned short-waves progress eastward.
With offshore flow and dry air ahead of the low, little
precipitation is making it into Southcentral at this point with
perhaps some areas of light snow in the mountains of southeastern
Prince William Sound and the Copper River Basin. Elsewhere across
Southcentral, the weather is quiet with considerable sunshine.
Lastly, a short-wave ridge is building eastward across the Bering
Sea and Aleutians, leading to benign conditions across the region.

&&

.MODEL DISCUSSION...

Models are struggling with the precipitation forecast over
Southcentral tonight through Friday, as the remnants of the low
over the eastern Gulf push onshore and the two short-waves and
associated cold air advection approach from the west. The 12Z NAM
is the biggest outlier, with a further east track of the Gulf low
and much drier precipitation forecast from Prince William Sound
to the Kenai Peninsula and Anchorage. Will generally use a broad-
brush approach with the PoP forecast. In any case, whatever
precipitation does fall will be light, with little snow accumulation.
Otherwise, model guidance is in good agreement with large scale
features over the next few days and forecast confidence is above
average.

&&

.AVIATION...

PANC...There is quite a bit of uncertainty in the precipitation
forecast, with potential for light snow sometime between 12Z Fri
and 00Z Saturday. If it does snow the intensity will be light,
but it would likely be enough to reduce cig/vis to MVFR for a
short period of time.

&&

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

Today's forecast revolves around two large-scale features and air
masses. The first is a mature, decaying low pressure system
moving westward along the north gulf coast. The system will spread
rain and snow from Cordova through Valdez and westward across
Prince William Sound with minimal accumulations. The second
player is a late-season arctic air mass over the southwest
mainland. High pressure will build in from the Bering Sea, while
the low pressure system moves westward, pulling that air mass
through the Alaska Range. The low pressure is quickly falling
apart, however it brings a saturated air mass that will interact
with the cold air coming across Cook Inlet, especially up against
the mountains. Snow will mainly be across the Chugach Mountains
through the Kenai Mountains, and will be fairly light.
Accumulations are not expected to be greater than an inch. Late
Friday into Saturday, dry air continues to come in from the west
with the arctic air bringing a cool but sunny weekend. Friday
night and through the weekend, outflow conditions will develop
along the north gulf coast bringing gusty north winds to the
favored locations from the Barren Islands through the Copper River
Delta.

&&

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

The troughing pattern over the Southwest region continues for the
next 24 hours before benign conditions commences for the weekend.
Multiple shortwaves pinwheeling on the southern end of a deep
polar low will work concert with low level convergence, thereby
bringing a period of snow showers for the inland valleys. The
forecast remains on track for the shower activity to come to end
by tonight across the eastern corridor of Bristol Bay and the
Lower Kuskokwim Valley. The rest will be favored for the upslope
areas along the Aleutian/Alaska Ranges and Kuskokwim Mountains
until early Friday morning.

As the trough axis pushes eastward across the western Alaska
mainland, the aforementioned polar low will usher an unseasonably
cold and dry airmass (850 mb temperatures around -20C) across all
areas. With mostly clear skies expected, overnight lows will be
in the single digits to below zero with daytime highs in the
teens. Temperatures are expected to rebound nicely for the weekend
as a ridge of high pressure and warmer airmass moves overhead.
Weak shortwaves riding on top of the ridge may bring a period of
light snow along the Y-K Delta coast Friday afternoon into
Saturday morning.

Meanwhile, a combination of colder air aloft, weak synoptic
forcing, and tightening pressure gradient will strengthen the
northerly winds beginning tonight across the Alaska Peninsula with
stronger gusts out of bays and passes. The winds will persist
over the next couple of days before subsiding by Saturday
afternoon. Otherwise, fair and mild weather will continue through
early next week as the ridge dominates the western mainland.

&&

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

A series of upper level waves embedded in the cold, northerly
flow over the relatively warm waters will help generate widespread
snow showers across the Bering Sea and Aleutian Islands. Another
weak band of snow showers will quickly pass overhead for the
Pribilof Islands late tonight into Friday morning, with little to
no accumulations expected. Drier conditions will commence
for the rest of the day Friday as a ridge of high pressure builds
across the Bering Sea.

By late Friday, a North Pacific low lifts toward the southern
Bering Sea, while another low lifts north toward the Kamchatka
Peninsula. The blocking ridge keeps the Kamchatka low from the
forecast area, with the exception of a brief period of small craft
winds across the western Bering Sea on Saturday. The North
Pacific low will push a swath of high end small craft to low end
gale force winds across the eastern Aleutian and Pribilof Islands
through the end of the weekend. Precipitation will initially
start out as rain/snow mix before changing to all rain as warmer
air surges northward.

&&

.Marine (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: Generally northwesterly flow is expected across
much of the Gulf Sunday through Monday night with potential small
crafts through the Barren Islands Sunday, diminishing Sunday night.
Small craft northerly winds are expected to develop especially
across the eastern Gulf Monday night and are expected to continue
through Tuesday. There is also the potential for low end gale
force winds, though, these winds are only expected to be in a
narrow corridor if they occur. Forecast confidence is good. Seas
are expected to be between 5 to 10 ft with the higher seas where
the stronger winds are.

Bering Sea: A well developed low pressure system over the North
Pacific moves towards the Western Aleutians Sunday night. The low
meanders through Tuesday with slow strengthening. Forecast
confidence is good. Widespread easterly winds with areas of gales
spread into the Bering through the day Sunday. Winds then shift to
southeasterly late Sunday night into Monday and then turn
southerly especially along the Aleutians Monday afternoon through
Tuesday. Seas build to 20 feet on the Pacific side of the
Aleutians on Sunday, before subsiding Sunday night, and to 15
feet over the Western and Central Bering through Monday, subsiding
Monday night.

&&

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

The dominant weather feature for next week will be a strong
blocking ridge over mainland Alaska. As is typical, model guidance
is struggling with run-to-run consistency with short-waves
tracking on either side of the ridge and timing of when ridge
will begin to weaken and/or shift away from mainland Alaska.
However, most solutions indicate the ridge holding through late
week. Based on this scenario, expect dry conditions over southern
Alaska, with abundant sunshine and normal to a bit above normal
temperatures. With mostly clear skies, large diurnal ranges in
temperatures will be the norm, leading to a daily freeze/thaw
cycle. While model spread is large, they do generally show the
ridge weakening late in the week, in which case one of the
bordering short-waves could usher in clouds and a chance of
precipitation.

Meanwhile, a long-wave trough will settle over the Bering Sea
and Aleutians, with a steady supply of storms tracking across
the region. Thus, expect wet and windy conditions through the
week. Depending on the position and strength of the ridge over
mainland Alaska, some of these systems could reach the Southwest
Alaska coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning: 130.
         Gale Warning: 131 132 138 150.
         Heavy Freezing Spray Warning: 130 138 160 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...MV/SEB