Gale Warning 333, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
413 PM AKDT Tue Apr 9 2024

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

An arctic trough extends from the North Slope south to the Alaska
Peninsula this afternoon. This trough is anchored by an upper-
level low situated over Kodiak Island. A compact surface low
pressure system continues to drive inland over the Kenai
Peninsula, producing another round of instability driven moderate
to heavy snow showers. Total snow accumulations through tonight of
several inches are expected from Seward to Whittier and Girdwood,
with snowfall rates approaching 1 to 2 inches per hour. A Special
Weather Statement is out for these areas. Total snow
accumulations will be tricky given the timing of the snow during
the day and temperatures right around freezing may limit
accumulations on area roads, with accumulations highly dependent
on snowfall rates. Scattered snow showers across the western Kenai
and the Anchorage Bowl will continue through early tonight with
light accumulations possible. Snow showers will also continue from
Cordova to Valdez, with the highest amounts in the mountains
surrounding both communities.

The upper-level low begins to weaken as it slides southeast on
Wednesday. Weaker and more compact surfaces lows will continue to
spin around in the gulf, and with influence from the upper low,
scattered snow showers will continue along the immediate coast.
Skies will clear out later on Wednesday for Cook Inlet up through
the Susitna Valley as a weak upper ridge briefly builds in from
the west.

A frontal system will push in Southwest Alaska Wednesday,
reaching the Cook Inlet and Susitna Valley area by Thursday
morning. Moist southwesterly flow and vorticity advection will
allow light snow to overspread the area, but downsloping will
quickly develop for locations in the lee of the coastal mountains
as low level southeasterly flow develops east of the new triple
point low. Multiple shortwave troughs and surface troughs embedded
within the main longwave trough will move in behind the initial
front for late Thursday into Friday. Colder air and a more
southwesterly flow ahead of the main trough axis will allow
precipitation to fill back in by late Thursday afternoon or
evening. Despite cold air aloft supporting snow, any snow
accumulation will be dependent on surface winds and temperatures,
especially during the day. Regardless, the coastal mountains will
see significant snow accumulation with this system. With a more
persistent southerly flow across the Susitna Valley, places like
Hatcher Pass and Broad Pass will also likely see significant snow
accumulations Thursday into Friday. A Winter Storm Watch has been
issued for north of Talkeetna, including Broad Pass, for Thursday
into Friday where upwards of 12" of snow is possible.
Precipitation will likely linger through Friday, possibly
including Anchorage as well, as the triple point low moves into
the western Prince William Sound.

-ME

&&

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

On satellite imagery (CIMSS MIMIC PW) there is fetch of Pacific
moisture that extends from Kamchatka to the Pribilof Islands.
Looking at Himawari (Airmass RGB) this moisture fetch is going
around a dome of high pressure to the east of it. One surface low
is actually over Kamchatka and the other surface low is over NE
Russia. Meanwhile the center of circulation for a 1042 mb high is
approximately 450 NM south-southwest of Adak but this feature is
clearly influencing that path of the moisture in the Bering.
Cold air will continue to filter south across Southwest Alaska and
eastern Bering/Alaska Peninsula. Gap winds south of the AKPen
will continue to be gusty through this afternoon and will
gradually diminish through tonight.

Snow and winds reach the Southwest coast early Wednesday morning
and increase significantly. A Blizzard Warning has been issued
for the Kuskokwim Delta, from Bethel west, for Wednesday, as wind
gusts are expected to increase to 50 mph and snow accumulation
will range from 7 to 10 inches. A Winter Weather Advisory for Snow
and Blowing Snow has been issued for the Western Capes of Bristol
Bay, including Togiak and Twin Hill for Wednesday as well, with
snow accumulations of 9 to 13 inches and wind gusts to 40 mph. The
warm air will eventually reach Southwest Alaska, however, snow
intensity is anticipated to be high enough to overcome
temperatures increasing to 33/34 degrees. The immediate coast is
the most likely to see transitions to rain during warmest
temperatures. Snow continues tracking inland by early Thursday and
values of 4 to 7 inches is possible across the lower Kuskokwim
Valley and interior portions of Bristol Bay.

&&

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

By Saturday morning, a deep upper-level trough will be moving
east over Southcentral Alaska, with weak ridging building over
the central Bering. This would lead to a widespread showery
pattern over the northern Gulf of Alaska and relatively calm
conditions over the Bering and Aleutians early this weekend. The
upper low and its attendant surface low will exit into Southeast
Alaska on Sunday. This will lead into a fairly benign pattern
across much of southern Alaska as the ridge once over the Bering,
shifts over our region, allowing for clearer skies and weak winds
across the area. By Tuesday morning, multiple low pressure systems
will approach the Chain from the northern Pacific. Model
agreement regarding the breakdown of a ridge is usually poor, and
remains so in this case, but either way, a significant shift in
pattern does not seem evident. A prolonged break in active weather
seems most likely currently for the latter portion of this
weekend into early next week.

-CL

&&

.AVIATION...

PANC...VFR conditions will be predominate, but there will be snow
showers in the vicinity which could include brief periods of lower
ceilings and visibility. Gusty easterly to northeasterly winds
ongoing this afternoon in response to mesolow tracking across the
southern Kenai Peninsula. There may be a brief period of winds
off of Turnagain Arm this evening, with higher confidence of
becoming lighter and turning from a northerly direction by
midnight. The Turnagain Arm winds will return late Wednesday into
Thursday.

MTL/PP

&&