310
FXAK68 PAFC 050049
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Sat May 4 2024

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

Southeast flow on the east side of an eastern Bering upper-level
low continues scattered light rain showers across portions of
Southcentral. This precipitation will gradually taper off through
tonight as the low continues to slide southeast. Gusty southeast
gap winds out of the Turnagain Arm and Knik Arms and Copper River
Basin will quickly diminish by early tonight.

The associated large upper level low with this system crosses the
Alaska Peninsula into the Gulf later on Sunday, with a weak ridge
building over interior Alaska. When combined with some weak upper
level easterly shortwaves and marginal instability, a few
weak/light convective showers may develop along the foothills of
the Wrangell Mountains/Alaska Range in the northern Copper River
Basin late Sunday afternoon into Sunday evening, however, this
threat is conditional on any clearing early on Sunday.

There is increasing agreement that these easterly waves propagating
along the southern periphery of the ridge will bring a steadier
rain to much of the region Sunday night into Monday, with some
model guidance hinting at a slowly westward progressing deformation
band across the western Kenai up through Anchorage and the Mat-Su
during the day Monday. This precipitation shuts off inland Monday
night as the main upper low flattens out, but southeasterly flow
will likely continue rain showers along the coast through at least
Tuesday.

Temperatures will remain near climatological averages, with highs
in the 50s for most of the region (except around 50 on Monday)
and lows in the mid/upper 30s to lower 40s.

-ME

&&

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

An occluded low will move eastward over the Alaska Peninsula this
evening and into the Gulf of Alaska tomorrow. It will continue to
bring a mix of rain and snow showers to the Aleutians, the Pribilofs,
higher elevation areas of both the Alaska Peninsula and coastal
areas of Southwest Alaska through the weekend. A primarily cloudy
sky with scattered rain showers will continue through tomorrow
afternoon for interior areas of Southwest Alaska and into tomorrow
evening for the Alaska Peninsula as northeast winds turn more
northwesterly. Northerly to northwesterly wind flow will keep
scattered snow showers through tomorrow in the Aleutians and
Pribilofs. These northerly winds will also result in freezing
spray for marine zones in Bristol Bay tomorrow evening.

A Bering Strait low will move southward through early next week
resulting in onshore flow along Southwest Alaska. This onshore
flow will bring a decrease in temperatures and increased chances
for coastal snow and rain showers changing to mostly snow showers
for Monday and Tuesday. A weak wave moving southward ahead of this
northern Bering Strait low will bring a resurgence of cold air
and snow showers to the Aleutians and Alaska Peninsula Monday
evening into Tuesday.

-DJ

&&

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

The long term begins on Wednesday with a broad trough stretching
from the western Aleutians/Bering across the North Pacific and
into the Gulf of Alaska. A closed upper-level low is located over
the Bering with weak low pressure at the surface, spreading light
precipitation across the region. A surface low over the
northeastern Gulf and an attendant upper shortwave quickly move
inland and are followed by another low/shortwave. Thus,
precipitation along the Gulf coast will persist into the weekend,
and agreement is very good amongst the models for above average
rainfall from Wednesday through Friday for the Southcentral coast.
The chance for heaviest precipitation along the coast is expected
on Thursday, with lesser amounts spreading inland through Friday.

Out west, a system from the Kamchatka Peninsula approaches the
western Aleutians late Wednesday into early Thursday. Model
agreement begins to diverge around this same timeframe. The GFS
and EC deterministic solutions drop the system south into the
North Pacific on Friday while the Canadian NH keeps the system
moving east across the Bering and Aleutians, which would bring
more active weather to the region. An upper-level ridge attempts
to build through the weekend across portions of the Bering and
Aleutians, and each model solution shows differences in the way
the ridge interacts with the surrounding lows/troughs.

&&

.AVIATION...

PANC...VFR conditions will persist. The biggest forecast challenge
is timing and duration of gusty southeast Turnagain Arm winds.
It`s another marginal day for winds to bend into the terminal due
to extensive cloud cover and fairly uniform temperatures from
Anchorage to the Mat-Su. However, the 00Z sounding shows unstable
conditions from the surface to 900 mb, with a lapse rate of 9
degrees C/KM. Thus, expect there will be at least a brief period
of gusty southeast winds as the Turnagain Arm jet can`t be very
far south of the terminal. For Sunday, expect more sunshine and
warmer temperatures inland, so there is higher confidence in
gusty southeast winds Sunday aft/eve.

&&


$$