959
FXAK68 PAFC 051325
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
525 AM AKDT Sun May 5 2024

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

A large low has transited from the eastern Bering into the central
GUlf in the last 24 hrs. Early morning water vapor imagery shows
several shortwave troughs rotating around the tightly wound parent
low. The eastern most shortwave is already lifting towards the
northern Gulf coast this morning with Middleton Island radar showing
more enhanced reflectivity moving westward along the coast towards
Prince William Sound. The the first half of today, much of the
precipitation will remain across the northern Gulf coastal areas,
Prince William Sound, and the eastern Kenai Peninsula. As the upper
low slowly lifts northwards today, several more shortwaves will
rotate around the periphery and up into the the southern Yukon and
Copper River Basin.

Ahead of this system, shortwave ridging extending westward across
interior Southcentral Alaska will help to funnel mid-level moisture
and warmer temperatures northward into the Copper River Basin today.
With several of these shortwaves lifting north then back west as an
easterly waves and marginal instability building today, weak forcing
should be more than ample to spark some convective showers along the
foothills of the Wrangells and Alaska Range by this
afternoon/evening. Models have trended towards a more widespread
area of showers developing over the northern Copper Basin and
translating westwards toward the Mat-Su Valley through Monday
morning. Both hi-res and med-range models are showing a deformation
band dipping down towards the Anchorage Bowl and the northwest Kenai
Peninsula; however, there are some hints that the heavier showers
may set-up just west of Anchorage over the northern Cook Inlet and
extending up into the Susitna Valley.

By Monday evening the low over the northern Gulf will begin to move
inland as more of an open wave, and besides some lingering showers
over the Susitna Valley and near-coastal areas of the Gulf, most of
Southcentral will see limited shower activity and mainly diurnally
driven.

- PP

&&


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

An occluded low continues moving eastward in the western Gulf of
Alaska this morning. Conditions will remain showery over the
southwestern mainland most of today and becoming more confined to
the higher terrain as the day progresses; especially near the
Western Alaska Range and Lower Kuskokwim Valley. Low stratus,
mist, and areas of fog will also linger over the Kuskokwim Delta,
and portions of Bristol Bay, especially around King Salmon and the
Western Capes this morning. Later today, a lightning strike or
two cannot be ruled out for areas around the Western Alaska Range
and eastern portions of the Lower Kuskokwim Valley due to day-time
heating and a little bit of instability. The caveat to this chance
would be if there is too much cloud cover this morning that does
not break up enough.

Northerly flow then ensues on the backside of the Gulf low as cold
air works in from the Bering Strait and Russia over the Bering
Sea for tonight and Monday. This colder air will work eastward off
of the Bering and into portions of the southwestern mainland
Monday morning where high temperatures will be in the mid 20s to
mid 30s with those coldest temperatures being along the Kuskokwim
Delta Coast and Nunivak Island. The Alaska Peninsula (AKPEN) will
also see cooler temperatures with highs in the mid 30s for Monday.
Interior locations of Bristol Bay and the Lower Kuskokwim Valley
see high temperatures in the 40s. Further to the west, a weak
North Pacific low will send its front to the western Bering and
western Aleutians Sunday afternoon through Monday with mostly
light rain expected. This system weakens and exits further south
into the North Pacific Monday evening.

Meanwhile, the strongest push of cold air through the Bering Sea
will be Monday into Tuesday morning. Freezing spray looks to be
likely through a good portion of the eastern Bering Sea zones and
Bering Sea side of the AKPEN for Monday. There could also be
pockets of Heavy Freezing Spray east of Saint Matthew Island and
west of Nunivak Island. Along with the cold air advection for
Monday, there will be snow showers likely for the Bering side of
the AKPEN and eastern Aleutians through Tuesday. As the new Bering
Sea upper-level low becomes more established Tuesday evening,
shortwaves will rotate around it and deliver the western and
central Aleutians a round of snow showers Tuesday into Wednesday
morning.

&&
.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. Chance for showers to move
over the terminal beginning this afternoon and persisting through
tonight. Gusty winds out of the south to pick back up late this
evening.


&&


$$