252
FXAK68 PAFC 080045
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKDT Tue May 7 2024

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

A weak upper level shortwave and surface heating this afternoon
has lead to showers and even some isolated thunderstorms over
inland, snow free areas. These will dissipate overnight as a
surface low in the southern Gulf moves north to the PWS over the
next 24 hours. This will increase cloudcover over most of the
forecast area for tomorrow, along with a steadier rain along the
coast. The upper level shortwave associated with the feature will
help to bring another round of showers to the foothills and snow
free valleys.

On Thursday the region will begin to come under the influence of
a deep upper level low and modifying arctic airmass. This trough
will move over the Alaska Peninsula on Thursday, wrapping cold air
in from the southwest. Snow levels will drop significantly with
chances increasing for snow accumulation above approximately
1000 ft, with snow falling and not accumulating at even lower
elevations. There is plenty of uncertainty in the forecast
associated with how the upper level trough breaks apart and sends
various shortwaves into Southcentral Thursday and Friday.

&&


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

A broad upper low has taken up residency over the northern Bering
on Tuesday with weak high pressure noted over Southwest Alaska
and also over the Western Aleutians. Despite mostly cloudy
conditions, much of Southwest Alaska has remained dry today. The
one exception being King Salmon, which is still experiencing a
steady band of light snow and reduced visibility down to less than
2 miles in the vicinity of a stalled boundary across Southwest
Alaska. Low pressure over the Gulf of Alaska has aided in the
movement of easterly wave activity along the boundary into
interior Bristol Bay, and forecast models suggest this precipitation
may continue into Wednesday.

Changes in the forecast are expected to begin as early as tonight
as a polar low near Saint Matthew Island drops southward through
the Bering. The low will bring cooler temperatures, gusty winds,
and snow to the Pribilof Islands through the morning hours on
Wednesday. The combination of winds and snow will result in
periods of reduced visibility down to one half mile. A Winter
Weather Advisory has been issued for the Pribs from 4am to 1pm
AKDT on Wednesday. The polar low will continue into the Eastern
Aleutians during the morning hours with gusty conditions expected
to linger into Wednesday evening from Nikolski to Unalaska.
Westerly gusts up to 45 mph will be possible. The arrival of
cooler temperatures will also see rain transition to snow, and
1 to 2 inches of total snow are possible by late tomorrow
morning.

After the polar low departs the Aleutians and moves into the
North Pacific, a Kamchatka Low is forecast to spread a broad
front into the Aleutians through Thursday night. Widespread
precipitation will accompany the front and span the Aleutian
Chain as it tracks from west to east, beginning Wednesday night.
Previously cooler temperatures over the Aleutians should lift
northward and become replaced by warmer North Pacific temperatures.
Thus, any initial snow will be brief and quickly transition to
rain.

&&

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

A broad upper level trough extends across the Bering and most of
Mainland Alaska through the forecast period. A weak upper ridge
moves out of the Russian Far East Sunday, but flattens out over
the Aleutians by Tuesday. Model guidance is good through late
Sunday, but becomes uncertain across the Aleutians as the ridge
collapses and a new overall flow sets up. A couple new features
out of Siberia begin to influence the pattern Tuesday. A well
developed upper low moves across the Alaska Peninsula into the
Gulf of Alaska by Sunday, then weakens and opens to a broad trough
for Tuesday. Its surface reflection moves from the Eastern
Aleutians into the Gulf, spreading a very active weather pattern
along its track Eastward.

Widespread precipitation spread across the Aleutians, AKPEN and
Southwest Alaska into Kodiak Island Saturday, and continues along
the Eastern Kenai Peninsula into Prince William Sound and the rest
of Southcentral Alaska through Sunday before tapering off in the
Western portions. Locally heavy rainfall is expected for coastal
locations from the Eastern Aleutians and AKPEN, over Kodiak Island,
and across to the Gulf into Monday, with decreasing amounts moving
inland. Gusty surface winds to just below gale force levels precede
the low across the Gulf through Sunday before diminishing. Breezy
conditions over the Eastern Bering and Bristol linger into Monday.

-Kutz

&&

.AVIATION...

PANC...VFR ceilings are expected to persist through Wednesday
morning. An isolated shower is possible later this afternoon and
evening near or at the terminal; however, the best chance for any
shower activity will likely be well north and west of the airport
complex. Gusty southeasterly Turnagain Arm winds will quickly
taper off by 06Z at latest as pressure gradients shift ahead of
a low tracking northward across the Gulf.

A series of upper level short-waves will lift northward toward
Southcentral tomorrow, leading to lowering ceilings during the
day Wednesday. Showers will develop by around 00Z Wednesday
afternoon, but will quickly transition to steadier light rain.
Expect ceilings to drop to at least low end VFR, with a chance for
a period of MVFR ceiling/vis, especially Wednesday evening.
Conditions look favorable for some low level convergence over west
Anchorage as southwest winds in Cook Inlet meet southeast winds
from Turnagain Arm. This also creates a challenging wind forecast,
as wind direction could vary from southwest to southeast. In any
case, do expect gusty winds to develop around the same time rain
arrives.

&&

$$