309
FXAK68 PAFC 210050
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKDT Sun Apr 20 2025

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

A high amplitude short-wave ridge extends from the Gulf of AK
northwestward across Southcentral to the west coast of AK.
A long-wave trough is centered over the Bering Sea with a zonal
jet along the Aleutian chain and southern AK Peninsula. There are
two distinct upper level lows and short-waves embedded within the
larger trough: one pushing up against the mainland AK ridge into
SW AK and the western Gulf/Kodiak; another deeper low/trough
progressing eastward along the western Aleutians and southern
Bering Sea. Both of these features will ultimately affect
Southcentral and the Gulf of AK. However, for now, the ridging
is leading to partly to mostly sunny skies across Southcentral.
Clouds are increasing from south to north as the upper trough and
weak occluded front approach Southcentral. Kenai radar shows light
rain progressing very slow northward across the Kenai Peninsula.
A trailing cold front is nearing Kodiak Island, producing a narrow
band of light rain. A light wind regime is in place across the
region. Coastal ridging ahead of the front combined with sunshine
inland is leading to development of gap winds along Turnagain Arm
into Anchorage, the Knik River Valley into Palmer, and along the
Copper River.

The upper level short-wave over Bristol Bay will initially progress
northeastward this evening, but with ridging to the north and
east it will then begin to shift eastward to the northern Gulf
overnight tonight through Monday morning. Precipitation will
gradually spread inland tonight out ahead of the trough, but with
the best lift out ahead of the trough shifting to the Gulf coast,
precipitation will be very light. Precipitation will be primarily
in the form of rain for the valleys, though interior Southcentral
will cool enough overnight to see some light snow - with little
or no accumulation.

Precipitation will diminish through the day Monday as the upper
trough exits eastward, lingering longest across eastern Prince
William Sound and the southeastern Copper River Basin. With fast
steering flow upstream, there won`t be much break between the
departing trough and the next one moving in from the Bering Sea.
Thus, mostly cloudy skies will prevail. An occluded front and
weak upper level short-wave will bring the next round to Kodiak
Monday afternoon. A short-wave digging into the North Pacific
Monday night will then cause the leading short-wave to lift
northward up Cook Inlet, with another round of light rain for
the Kenai Peninsula and western Susitna Valley Monday night into
Tuesday.

The amplification of the upper level flow will lead to development
of a surface low south of Kodiak Island Tuesday morning. This low
will track into the Gulf and deepen as the upper center transitions
from the Bering Sea to the Gulf Tuesday night- Wednesday. There
is some uncertainty in the low track, but high confidence that it
will quickly occlude and become vertically stacked, causing it to
stall somewhere in the central Gulf. Thus, the bulk of impacts of
rain and winds will be confined to Kodiak Island and coastal areas
of Southcentral. Inland portions of Southcentral will be mostly
dry, but with considerable cloud cover.

-SEB

&&


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

This afternoon, the main weather story is a shield of rain
continuing to overspread the Southwest, with temperatures just
cold enough for Nunivak Island and the Kuskokwim coast to support
a rain/snow mix or all snow. Warm air advection continues to spill
into the region with this first wave, including the Eastern
Aleutians and AK Pen, where both areas have had temperatures
surpass 40F today. Cold Bay has been persistent in being quite
gusty throughout the afternoon, and St. Paul has seen reduced
visibility and cloud ceilings with fog and mist.

As St. Paul improves this evening, areas of fog are possible for
Nunivak Island and the Kuskokwim coast tonight into Monday
morning. Elsewhere, a broad Bering complex low with its associated
trough draped eastward across the Bering finally begins to gain
some momentum and moves eastward through the day Monday. A
shortwave rounding the southern periphery of the low on Monday
brings elevated winds back to Cold Bay and another wave of
precipitation to Southwest Alaska, as the center of the low itself
nears Nunivak Island. Again, temperatures are marginal for this
area, but could support some additional snowfall while the Bristol
Bay coast and the inland Southwest temperatures stay relatively
mild with rain.

However, as the low swings through the area Tuesday, colder air
aloft attempts to wrap in with a northwesterly wind for the
Bering, Central, and Eastern Aleutians. Shortly thereafter, a
transient ridge slides across the region out ahead of yet another
gale force frontal system arriving to the Western Aleutians by
Wednesday morning.


-AM

&&

.LONG TERM FORECAST (Days 4 through 7/Thursday through Sunday)...

A very broad upper level weather pattern with several low centers
and a number of differently oriented troughs extends across the
region. Divergence aloft continues as the pattern weakens and
becomes more zonal through the forecast period. Most of the active
weather will be occurring across the Southern portions of the
state into the weekend. A weak upper ridge builds over the weekend
across Southeast Alaska and Western Canada. A loosely organized
mix of ECMWF / GFS / UKMET and Canadian models carry the main
features quite well, although the GFS hold onto a track to the
South of the other models along the same axis of movement.

A decaying surface low in the Southeastern Gulf of Alaska slips
further South, but leaves a weakening front wrapped along the
North Gulf Coast from Kodiak Island to the Canadian border.
Locally moderate rain remains over the coastal zones through
Thursday. A Western Bering surface low extends a front into the
North Pacific and slips Eastward with snow along its Northern
edges, and rain elsewhere through the weekend. Areas of freezing
rain are expected South of Nunivak Island through Saturday. A
developing North Pacific low picks up the frontal weather and
pushes it over the Alaska Peninsula and Kodiak Island late
Saturday into Sunday. Scattered showers are expected across the
Kenai Peninsula and Southcentral Alaska Sunday. A well developed
low and front approach the Western Aleutians and Bering for Sunday
with another round of rain expected.

- Kutz

&&

.AVIATION...

PANC...Southeast winds gusting to 20 to 30 knots from Turnagain
Arm over the terminal this afternoon are expected diminish around
midnight. VFR conditions will last through the rest of today with
increasing clouds late this afternoon and evening. Rain becomes
more likely after midnight and ceilings look to drop into MVFR
around 16Z Monday. While weather and ceilings will improve by
Monday afternoon, the Turnagain Arm winds will return with gusts
20 to 30 knots.

&&


$$