676
FXAK68 PAFC 211239
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
339 AM AKST Thu Nov 21 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

The dominant feature for Alaska Weather is a strong closed upper
level ridge centered along the southern Alaska Peninsula.
Anticyclonic flow and associated sinking motion extends across
the eastern Bering Sea and all of southern Alaska and the Gulf
of Alaska, leading to "bone dry" conditions. Warm (above freezing
air) aloft moved over the ridge into Southcentral yesterday. The
airmass has warmed further due to northerly downslope flow along
the east side of the ridge. A look at temperatures across
Southcentral mountain locations bears this out, with above
freezing temperatures from Hatcher Pass to the western Chugach
Mountains to the Kenai Mountains. The warmest temperatures are
over the eastern Kenai Peninsula Mountains, with widespread 40s.
Meanwhile, temperatures down at sea level remain well below
freezing with single digits below zero in the southern Susitna
Valley to single digits (above zero) and teens as you head south
to the Kenai Peninsula. The exception is coastal locations like
Whittier, Seward, and Kodiak where downslope winds are mixing
down the warm air to the surface. The airmass over the Copper
River Basin remains quite a bit cooler, with temperatures well
below zero in the Copper Valley. Robust low level northerly flow
along the east side of the ridge is combining with surface
pressure gradients to maintain fairly strong and gusty winds along
coastal gaps. The steep temperature inversion in place on the
eastern Kenai Peninsula seems to be promoting downward
acceleration of the winds along the coast, with wind gusts as high
as 50 to 60 mph in both the Seward and Whittier areas.

The weather will remain quite stagnant for the next few days as
the ridge remains upstream of Southcentral. The ridge center will
slowly shift southward into the North Pacific, but anticyclonic
flow over Southcentral and the Gulf will remain strong. Today will
likely be the warmest day in the mountains, with slight cooling
as a ridge axis over Southcentral shifts south late today.
However, the areas which are above freezing now will likely remain
there. Inland valleys will see a slight warming, but will largely
remain below freezing. Gap winds will keep going along the coast,
though as the ridge shifts a bit further east this weekend, low
level flow will weaken and pressure gradients will loosen. This
will lead to weakening of all coastal gap winds. Other than some
occasional mid to high clouds passing through, conditions will
remain dry.

-SEB

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING SEA/ALEUTIANS
(Days 1 through 3: Today through Sunday morning)...

The large ridge over the eastern Bering will begin to weaken with
the core shifting south into the North Pacific Friday and
Saturday. Low stratus and fog will continue this morning for
portions of the Kuskokwim Delta and Lower Kuskokwim Valley with
the potential for it to linger into Friday morning. The one
caveat against fog is that surface winds will turn northeasterly
and off-shore today which could advect in slightly drier air from
the interior helping to lower dew points. However, the overall
airmass and ridge position today into Friday morning will change
very little. Elsewhere across Southwest, expect mostly scattered
high clouds today through Saturday.

A series of shortwaves continues to deliver light rain and
southeast winds to the Western Aleutians this morning. This
activity is expected to clip Adak later today. A shortwave coming
off of Kamchatka will interact with a shortwave in the North
Pacific late this evening into Friday morning and cause a surface
low to spin up across the Western Aleutians Friday morning. This
will help to enhance showers and winds across the both the
Western and Central Aleutians Friday as the front pushes eastward
with time. Pockets of gale-force winds are possible across the
Central Aleutians Friday with mostly small-craft winds expected.
Pockets of gale-force winds are expected across the western
Bering Friday evening into Saturday morning on the backside of the
system.

The initial front weakens as it reaches the Pribilof Islands
Saturday. However, the main trough across the western Bering will
begin to dig further into the North Pacific Saturday afternoon and
evening which will help pull more moisture northward. This
additional moisture surge looks to mainly affect portions of the
Central Aleutians (Atka) and the Pribilof Islands with steadier
rain late Saturday night into Sunday. The front also makes it to
the Kuskokwim Delta coast and Nunivak Island Saturday and remains
stationary into Sunday morning. The resulting weather for now
looks to be showers for Saturday with potentially more wide-spread
and steadier rain for Sunday across the Kuskokwim Delta coast.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

The Alaska Weather map will become a bit more elastic and active
as a strong shortwave ripples across the top of the Interior
Alaska upper level ridge through Tuesday. The Bering shortwave
extending from an Anadyr low moves over the ridge into Canada for
Tuesday. The ridge resets over the Western Mainland through
Wednesday. Areas of moderate rain and some gusty winds spread over
the Western and Central Aleutians on Sunday before the system
moves over the Bering. This system will turn Eastward, briefly
flattening the ridge. Most of the Southern Interior is expected to
have light winds, overall dry conditions and somewhat moderate
temperatures in the zonal flow over the lower half of the state,
although coolest overall temperatures should linger over the
Eastern Interior through Tuesday. Precipitation, if any, will be
light and intermittent through the weekend with a very small and
brief risk of freezing precipitation over Interior locations.


&&.AVIATION...

PANC...VFR conditions and light winds will persist.

&&


$$