102
FXAK68 PAFC 111231
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 AM AKDT Tue Mar 11 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tuesday through Thursday evening)...

A 986 mb compact, occluded surface low has been quasi-stationary
overnight, situated due south of Middleton Island and due east of
Kodiak City. A deformation band of snow over Kodiak Island
overnight has moved southeast this morning, with snow tapering off
for most places on the island. A core of gale-force winds remain
southwest of center of circulation; however, winds over the
northern and western Gulf are beginning to diminish in intensity
as the low slowly weakens.

Elsewhere, low clouds and isolated to scattered rain/snow showers
continue to move westward across the northern Gulf. The showers
inland over the coastal mountains have tapered off overnight;
however, low stratus continues to linger over the Chugach and
Kenai Mountains. Scattered mid and high clouds over interior
Southcentral have done little to keep overnight low temperatures
elevated, with temperatures early this morning ranging from 18 to
32 degrees from Homer north to Talkeetna to near 0 for the central
Copper River Basin.

The Gulf low is still expected to drift southeast through today,
taking the bulk of the lingering shower activity with it.
However, isolated to scattered showers are expected to develop
later today across the Central Chugach and Copper River Basin,
especially at elevation, as an upper-level trough slides
southwest from the Al-Can border. Multiple vorticity maxima will
rotate underneath the upper-level trough, providing some increase
in instability, as upper-level diffluence increases over these
areas along with an increase in moisture advection from the
lingering low-level moisture over the northeastern Gulf.

Model uncertainty then increases dramatically beginning early
Wednesday morning as the upper-level trough continues to slide
south with yet another area of vorticity advection moving south
from the Susitna valley in conjunction with cold air advection
spilling over the Alaska Range and across the Barren Islands. The
result will likely a strengthening of a mid-level wave over Cook
Inlet or the Kenai Peninsula and the development of an inverted
surface trough or compact meso-low somewhere southeast of Seward
Wednesday morning. Bottom line, most guidance, especially hi-res,
are hinting at the development of a band of precipitation, mainly
in the form of snow, somewhere over Prince William Sound early
Wednesday morning getting drawn northward through the day.

That said, the GFS is a slower solution with snow developing first
over the southeast Copper River and Cook Inlet, before a later
spin up of the meso-low and delayed timing of an area of more
concentrated area of snow in Prince William Sound. The EC keeps
the precipitation farther west and the RGEM and ARW eventually
slides the heaviest precipitation eastward by Wednesday night.

The forecast reflects the likely spin up of the meso-low and the
bulk of precipitation over the sound and lifted northward. For
places west of the Chugach and Kenai, the forecast leans toward
flurries, with little to no snow accumulation for Wednesday. This
is also due to a colder and drier northerly flow developing in
response to the cold air advection. Several inches of snow are
possible, though, for the eastern Kenai east to Valdez and north
to Eureka through Thursday.

-TM

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Thursday night)...

A broad longwave trough is keeping a cooler, relatively unstable
air mass extending across the state this morning. Between a weak
ridge extending up into the central and western Bering Sea from
the North Pacific and broad low pressure in the Gulf of Alaska,
colder air streams down across the central and eastern Bering,
producing a mix of rain and snow showers. A mesoscale low embedded
in the broader circulation in southern Bristol Bay tracks across
the Alaska Peninsula later this morning and opens into a trough.
Enhanced gusty winds and shower activity to the south and west of
the low diminish through the day as the low exits the region,
falling below gale force by this afternoon. However, a burst of
cold air crossing the Alaska Peninsula behind the low leads to gap
winds from Chignik east accelerating up to 30 knots this
afternoon and evening. As weak ridging moves into the area
overnight, expect these winds to diminish through Wednesday
morning.

Further west, a large North Pacific low lifts a front into the
central and western Aleutians beginning this afternoon. Low-level
temperatures will initially be cold enough for precipitation to
fall as snow while easterly winds along the front increase into
low-end gale force range. However, temperatures will steadily
warm overnight into Wednesday morning, allowing snow to change
over to rain after midnight for Adak and Atka. Surface
temperatures hovering in the mid 30s are likely to prevent
significant blowing snow for Tuesday night, but an inch or two of
snow accumulation will still be possible before the changeover to
rain early on Wednesday. The low and front continue east towards
the southern Alaska Peninsula Wednesday into Thursday. Easterly
winds diminish below gale force on Wednesday as a rain/snow mix
shifts into the eastern Aleutians and southern Alaska Peninsula.
Wednesday night, northerly winds draw cold air from the Bering Sea
back across the Aleutians, turning precipitation back to snow for
the central Aleutians overnight, with locations further east
seeing rain transition to snow on Thursday.

For Southwest Alaska, expect much quieter and drier conditions as
the main weather feature to affect the area will be a deep upper
low that brings an increasingly colder air mass from the Interior
through the week. Areas of low stratus and fog over Bristol Bay
should tend to clear up from north to south as light northerly
flow develops through Tuesday morning. Temperatures will steadily
cool each day as northeast winds advect cooler air into the region
from the Interior along with clearing skies through at least
Thursday.

CQ/AS

&&


.LONG TERM FORECAST (Days 4 through 7 - Friday through Monday)...

The forecast opens with a somewhat convoluted upper level trough
extending from Siberia to the Central Aleutians, then curving over
Mainland Alaska into the Northern Canadian Provinces. This
pattern draws down to a smoother medium amplitude trough by the
end of the forecast period. An upper level low transits the Gulf
of Alaska before slipping Southeast by Sunday. A weak upper ridge
rides over the Aleutians into the Eastern Gulf by Monday. A
clustered ensemble of GFS / ECMWF and Canadian maintains good
support through the weekend, with some increased uncertainty over
the North Pacific where models diverge for the new week.

Most of Interior Alaska remains free from precipitation through
the weekend. A series of weak surface lows slide along the
Aleutians and Southcentral areas, bringing rain, mixed rain and
snow or snow over the Aleutians and Alaska Peninsula, and
continuing along the Southcentral coasts into Prince William Sound
and the Copper River Delta, diminishing Sunday. A well developed
North Pacific low and front moves along the Aleutians to Kodiak
Island by Monday, injecting some locally moderate precipitation
over the Aleutians late Saturday and Sunday, moving Eastward to
the AKPEN and Southcentral through Monday. Some areas of snow
spread inland over Southwest Alaska Sunday and Monday.

- Kutz

&&


.AVIATION...

PANC...VFR conditions and light winds will persist. Due to lighter
winds aloft and a weak low over Prince William Sound, light snow
is possible after 12z Wednesday which may drop ceilings below 5000
ft at times.


&&


$$