378
FXAK68 PAFC 201341
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
541 AM AKDT Thu Jun 20 2024

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

An upper-level shortwave and associated surface trough will move
from the northern Gulf this morning over interior Southcentral by
late afternoon. Mid and high level clouds will be on the increase
this morning from south to north as both features advance toward
the region. Showers will also move toward the coast this morning,
with showers and isolated to widely scattered thunderstorms
developing across the Copper River Basin and Talkeetna Mountains
later today as the wave first lifts north then rotates to the west
through this evening. The best chance for thunderstorms today will
be along the mountains and foothill of the northern periphery of
the Copper River Basin. Showers and isolated thunderstorms may
also extend into the northern Susitna valley for this evening, but
confidence on the extent of convection is low given the likelihood
for increased cloud cover over the region by that time, helping to
inhibit convective development. Southerly gap winds will also
develop by late afternoon or early evening in the wake of the
upper-level wave.

A second upper-level wave looks to move across the region for
Friday. Models continue to struggle with the strength and exact
track of this feature; however, it does look like there is again
the potential for isolated thunderstorms over much of the same
areas as is expected today. This second feature does look to track
in a more east-west then southwesterly fashion. If it does, there
is a better chance for some showers, and perhaps isolated
thunderstorms, to move off the Talkeetna Mountains and across the
Susitna Valley for Friday evening.

-TM

&&


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

A low in the North Pacific will continue to bring southerly to
southeasterly winds into Southwest. This will result in
widespread rain showers and a mostly cloudy sky to persist over
the area today. The chance of an isolated thunderstorm, highly
dependent on cloud breaks and the track of a short wave moving
through the area is highest near and north of Sleetmute this
evening. The chance of a thunderstorm is 20%. Elsewhere today,
isolated rain showers, fog and low ceilings will be widespread in
the Aleutians, the Alaska Peninsula and coastal areas from Toksook
Bay to Dillingham through late this morning. Scattered rain
showers are expected in the Eastern Aleutians and the Alaska
Peninsula through the evening hours with drier conditions in the
Central and Western Aleutians this afternoon and evening.

The north Pacific low enters the Gulf resulting in a more
southerly wind flow into Southwest Alaska tomorrow. The southerly
flow will aid in more cloud breaks and multiple waves crossing
the region. The chance of isolated thunderstorms range from 15 to
20% across the Western Alaska Range and the Kuskokwim Delta
in the late afternoon and evening hours. Elsewhere, a ridge
begins to build into the Western and Central Aleutians continuing
the possibility of fog over the area. This ridge will slowly move
eastward as a low travels south of the Western Aleutians arriving
south of Adak tomorrow evening.

Saturday, the ridge in the Central Aleutians moves over the
Eastern Aleutians and the Alaska Peninsula through the morning
hours as the North Pacific low migrates east of Adak. Southerly
flow, fog, low clouds and rain will signal the departure of the
ridge and the arrival of the low. Isolated rain showers and
thunderstorm chances remain in the KW Delta and Western Alaska
Range.


-DJ

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

Three main low centers on the upper air charts demonstrate the
most energy through the forecast period. A slowly retrograding low
over the Chukotsk Peninsula continues into Siberia. The second is
a Western Bering low, the next of a series that have moving
across the North Pacific, that will track across the Alaska
Peninsula by midweek. The last is a low center just South of the
Aleutians that will slide across the Southern Gulf of Alaska/
Eastern North Pacific for Wednesday. Most of Mainland Alaska is
under a weak ridge which supports surface thermal troughs and
areas of convection across the Interior for the entire forecast
period. Showers are expected across Southcentral. A series of
surface low and fronts bring mostly showery conditions along the
Aleutians, Bering and AKPEN, spreading into Southwest Alaska
through Wednesday. The next surface low from the North Pacific and
its front enters the Aleutians and Bering Tuesday, and move over
the Central portions by Wednesday. locally heavier precipitation
and gusty winds up to gale force spread into the Central
Aleutians.


-Kutz

&&

.AVIATION...

PANC...Winds will start out southwesterly this morning and
transition to a more southerly and even a south-southeasterly
component through the day as the Turnagain Arm jet strengthens.
Generally, during the afternoon and early evening hours is when
the gustiest of the winds are expected which is coincident with
peak day-time heating. However, there is uncertainty in the exact
onset of gusty south to southeast winds. Regardless, gusts are
expected to die down overnight tonight with the loss of
instability and day-time heating. Pressure gradients slacken by
Friday morning with the return of more light and variable winds.

Meanwhile, VFR ceilings will prevail through the TAF period. The
Turnagain Arm jet and associated easterly flow aloft will help to
keep ceilings higher than 5,000 feet. However, there will be a
number of short-waves lifting over the area through the TAF period
with mid to high-level clouds expected. Precipitation should stay
out of the terminal due to the downslope drying effects of the
easterly to southeasterly flow aloft. The bulk of precipitation is
expected to fall along Prince William Sound and the Gulf Coast.

&&


$$