Gale Warning 601, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 AM AKDT Sat Sep 7 2024

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

Discussion:

Scattered showers are starting to wind down across the Gulf as the
quasi-stationary low starts to push eastwards in response to a ridge
building over western Alaska this morning. Low stratus and fog have
started to develop along the western Kenai Peninsula per nighttime
microphysics RGB satellite imagery, especially in areas that
received heavier rainfall from yesterday's convection. Expect the
low stratus and fog to continue to spread along the Cook Inlet and
into the lower Susitna Valley by mid-morning. Some areas could see
stratus and fog linger into the afternoon as the ridge builds in,
but most areas should be able to mix out later this morning.

A shortwave trough moving across the Northern Slope and its
attendant front are starting to spark a round of showers this
morning across the Tanana Valley and northern slopes of the Alaska
Range where stronger forcing is positioned; however, there is a good
chance that scattered showers may extend down into the northern
Susitna Valley and the northern Talkeetna Mountains this
morning...moving towards the northern Copper River Basin by this
afternoon.

Another low up near Kamchatka will send its front sweeping eastwards
across western Alaska today, and while this front will be quickly
weakening as it approaches Southcentral...will see more widespread
showers work over the Alaska Range into the Susitna Valley by Sunday
morning. On the heels of that system, a quick moving disturbance
(the extratropical remnants of former Tropical Storm Leepi) will
move through near-zonal flow Sunday bringing another round of more
widespread rainfall to portions of Southcentral. Models are
struggling to handle this system, both in terms of the strength of
the mid-level wave and the track of the system as it moves across
the AKPen and ejects out into the Gulf. The NAM favors a more
northerly track with rain spreading up the inlet and into the Mat-SU
Valley. The GFS and GEM have the low further south with much of the
heavier rainfall remaining confined to the Gulf coastal regions. The
ECMWF is the farthest south solution and would keep the bulk of the
precipitation over the Gulf.

- PP

&&

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

A front currently over the Pribilof Islands will move east today,
pushing into a shortwave ridge currently over Southwest Alaska.
This ridge, and mostly calm winds over the Mainland, have allowed
more fog and low stratus to develop, but it's not quite as
established as Friday. As the front moves east, it will bring light
rain to the Kuskokwim Delta before the front really breaks down
over Bristol Bay and the Interior. These areas will likely see
some light rain, but little accumulation.

Quickly on the heels of todays front will be a quick moving
shortwave embedded in a ~120kt zonal jet streak. Pockets of gales
will surround the somewhat compact low. Rain will start out on
the heavier side near Shemya tonight due to the tropical origins
of the former tropical depression Leepi, but expect intensity to
lessen as it moves east and cooler air is slowly entrained into
the system. The center of the low is expected to be over/near the
Alaska Peninsula late Sunday night and into Monday morning, but
the north/south positioning amongst the guidance is still 50 to
100 miles apart. This forecast package represents a position
close to the ensemble mean and the GFS track.

-CJ

&&

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

On the Alaska Weather map, a weakening closed surface low in the
Southern Gulf of Alaska exits to the Southeast late Tuesday. The
Canadian and UKMET forecast models lag behind the rest, while the
ECMWF and GFS carries the features well through midpoint, with
model means picking up the features through the end of the
forecast period. In the West, an upper level low in the Russian
Chukchi Sea extends a trough through the Western Aleutians and
Bering that moves into Western Alaska and the Alaska Peninsula for
Wednesday and across Mainland Alaska to the Canadian Border by
Thursday. High pressure moves over the Interior of Alaska through
Friday morning. The Southern portion of this system on the surface
gains a little boost from a former tropical system merging near
the Central Aleutians and continues with the surface front into
and across the Gulf of Alaska through Thursday. Following behind,
a well developed surface low moves across the Northern Sea of
Okhotsk and extends a second front into the Western Aleutians and
Bering late Wednesday. This front starts to dissipate as it swings
into the Northern Bering by Friday morning.

Gusty winds to near gale force spread along the the North Gulf
Coast and Northern Gulf through late Wednesday. Areas of moderate
rain spread from Western Alaska into the Central Interior before
diminishing Wednesday. The Central and Eastern Aleutians will see
periods of moderate to heavy rains as the surface low moves over
the Alaska Peninsula into the Western Gulf Wednesday night. This
low brushes past Kodiak Island with lesser rainfall to bring
another round of moderate to heavy rains to portions of the
coastal zones over the Eastern Kenai Peninsula, Prince William
Sound and the Lower Copper River Valley. Lesser amounts of rain
spread further inland. Higher elevations look to gain some
additional snow cover with this system's passage. Gusty winds
accompany the second front across the Western Aleutians and Bering
Thursday through Friday.

- Kutz

&&

.AVIATION...

PANC...VFR conditions are expected for the forecast period. Very
localized fog in the vicinity is possible in the morning hours,
but is not expected to impact the terminal. Otherwise, ceilings
will generally remain above 5000 ft.

Light southeasterly winds with occasional stronger gusts expected
through the morning, with gusts to 20 kt becoming more frequent
this afternoon and evening. However, there is lower confidence in
the timing and magnitude of these gusty southeasterly winds.

-JR/KC

&&