310
FXAK68 PAFC 211256
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Fri Jun 21 2024

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

No significant changes to the previous discussion...

Key Messages:

* Warmer temperatures and an increase in thunderstorm activity
  coming to Southcentral this weekend.

* Gusty offshore winds in Resurrection Bay and Passage Canal
  Friday night through Saturday morning.

* Gusty northerly winds across the northern Susitna Valley and
  northern Copper River Basin on Friday night through Saturday.

Looking at satellite imagery, the key weather features are a
vertically stacked low in the northeast Pacific tracking into the
Gulf of Alaska and a north-south oriented upper trough stalling
over the Southwest Alaska coast. A second wave is situated along
the Alaska-Canada border, just north of the Alaska Range. The bulk
of the shower and thunderstorm activity has diminished overnight
and remains focused along both the trough over Southwest and
underneath the Al-Can wave.

Today, the atmospheric flow over Southcentral will back around to
the northeast in response to the Gulf low progressing eastward
and the upper trough over Southwest rotating northwestward.
Clouds will diminish along the coast, while the northerly
component to low level flow results in warming temperatures and
establishment of a thermal trough over interior Southcentral. This
will result in an uptick in showers and thunderstorms this
afternoon and evening, though the bulk of them will remain inland.
Storm motion will generally be from northeast to southwest.

Continuing to Saturday, an upper level ridge will strengthen
somewhere over the Alaska Interior. Model guidance continues to
vary on the center of the ridge, with most guidance placing the
center over the western Interior. This will bring even stronger
northerly flow to Southcentral Friday night through Saturday,
leading to additional warming and destabilization of the
atmosphere. Locally gusty offshore winds are expected along the
coast and along the Alaska Range into the Susitna Valley and
Copper River Basin, contributing to very warm and dry conditions
region-wide (probably not quite as hot as last Saturday, but not
too far away). Showers and thunderstorms will form inland and
track toward the coast the late afternoon and evening hours,
potentially including Anchorage once again.

While Sunday continues to look warm with afternoon/evening showers
and thunderstorms, there is quite a bit of model spread in
location of upper ridging and troughs. Thus, it difficult to nail
down the preferred areas for convection and overall storm motion.

-SEB/TM

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS
(Days 1 through 3: Friday morning through Monday morning)...

The big picture of the forecast remains largely unchanged, though
there have been major updates to the precipitation and
thunderstorm forecast for Southwest Alaska as we continue to
assess more data. Expect thunderstorm chances to persist through
the weekend for Southwest Alaska, along with a general warming
and drying trend. For the Bering Sea and Aleutian Islands, most
areas will see light winds less than 25 kt as the ridge moves east
across the Bering Sea, and incoming lows remain on the periphery
of the forecast area.

This morning, showers move offshore from the Kuskokwim Delta and
south to the Alaska Peninsula by this afternoon. Thunderstorm
chances for mainland Southwest continue through the weekend,
though forecast confidence decreases appreciably for Saturday and
Sunday afternoon. Expect storms to generally move from north to
south both Friday and Saturday afternoons as steering flow aloft
becomes more northerly. Shower coverage gradually diminishes this
weekend as the upper level ridge moves in. Afternoon and evening
highs will climb into the 70s under this ridge, with the potential
for temperatures to even approach 80 on Monday.


&&


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

A number of changes come to light on the Alaska Weather map
through the forecast period. The upper level low over the Russian
Far East curves towards the Sea of Okhotsk and dissipates late
Tuesday. Its extended trough forms another low over the Western
Aleutians and Bering for Wednesday, and moving to the Central
Bering for Thursday. A third low in the Eastern North Pacific
exits along the Canadian coast for Thursday. A shortwave ridge
over the Eastern Aleutians and Bering moves over Southcentral
Alaska and reinforces an Interior ridge through Thursday. Model
agreement in the geographic broad brush is good, but becomes
somewhat chaotic in the finer details. ECMWF/GFS are closest in
the details, the Canadian model runs low and slow.

A well developed low and front spreads locally heavy rain and
gusty surface winds less than gale force across the Aleutians and
Bering, impacting the Pribilofs and Eastern Aleutians for midday
Tuesday, and into Western Alaska, the Alaska Peninsula and Kodiak
Island through Thursday. Surface thermal troughs support some
convection across the Southcentral Interior South of the Alaska
Range. Areas closer to the coast will see isolated to scattered
showers through Thursday.


-Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Light
and variable winds this morning will turn more westerly by mid-
day today as the sea breeze kicks in coincident with day-time
heating. The terminal should stay dry today with convection
staying further to the north over the Talkeetna Mountains and
Chugach Mountains. Southwesterly winds will turn more light and
variable overnight tonight into Saturday morning.

&&


$$