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FXAK68 PAFC 271308
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 AM AKDT Wed Aug 27 2025

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

IR and WV satellite imagery this morning reveal a train of
shortwaves in the upper levels moving northeast from the North
Pacific into the Southern Mainland, embedded in the southwesterly
flow between a digging upper-level trough over the eastern Bering
and a stout upper-level ridge extending north along the coast of
the western U.S. and Canada.

The first of these waves is moving into the Copper River Basin,
and was the wave responsible for the periods of rain across the
Kenai Peninsula, Anchorage Bowl, and Mat-Su Valleys yesterday
evening through the overnight hours. The second, is quickly moving
across the AKPen toward Cook Inlet and is brining rain to
Southwest Alaska and Kennedy Entrance south to Kodiak Island. This
is the feature that will bring another round of steady rain from
Cook Inlet north into the Susitna Valley and east to Prince
William Sound later today.

At the surface, a low has developed along an old frontal boundary
south of the AK Pen. The center of this low will gradually lift
from Bristol Bay this morning into the Y-K Delta this afternoon.
The strong pressure gradient between this and the ridge to the
east will shift, allowing strong gap winds to again develop by
late morning, continuing through later this evening before
shifting to a more east-west orientation as the next low spins up
south of the AKPen and shutting off the gap winds, similar to what
was observed last night and this morning.

The forecast is on track with respect to this second low, as the
upper-level wave from the North Pacific phases with another wave
driving east underneath the digging upper-level trough moving over
the Aleutians and AK Pen. The shortwave will strengthen rapidly,
aided by a 130kt north-south oriented jet streak, and will also
tap into a tropical moisture feed. At the surface, the low will
spin up, strengthen, and drive northward into Bristol Bay. Its
front will slowly move from the western Gulf to Prince William
Sound through Thursday, and then stall over Prince William Sound
for Friday before finally exiting the region. Multiple shortwaves
will ride along the front, helping to enhance precipitation along
the coast and over most of Southcentral. Gap winds will also
continue through the week given the storm track, with the
strongest gusts likely Wednesday and Thursday afternoon and
evening. Gusts across favorable gap locations could range between
30 and 50 mph. While some lulls may be expected given the
seemingly ever-shifting axis of the pressure gradient, these gap
winds will peak in intensity by late Thursday morning as the low
lifts across the Kuskokwim Valley. Winds at ridgetop level will
also rapidly increase during this time with gusts of 50 to 65 mph
not out of the question for the hillsides of Anchorage and Eagle
River.

Rainfall amounts are also on track for these upcoming systems,
with perhaps slightly higher amounts than initially thought. This
is true given the amount of moisture advecting into the region and
the slower eastward track of the surface low and upper-level
trough depicted in the latest EC and GFS runs (favored over the
NAM and GEM solutions). For Wednesday through Saturday morning,
rainfall totals could top out between 3 and 6 inches for coastal
locations from Seward to Cordova. 2 to 4 inches of rain could fall
across the Susitna Valley along with 1 to 3 inches for coastal
western Kenai Peninsula. Upwards of 1 to 2 inches of rain is
possible for the Anchorage Bowl and Matanuska Valley, as the
strong dynamics with this system helps to negate any downsloping
from the southeasterly winds closer to mountaintop level. Around
one half to one inch of rain is also possible for the Copper River
Basin Friday into Saturday.

-AM/TM

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: This morning through Saturday morning)...

Active weather continues through the end of the work week. The
most impactful weather will be focused on Southwest Alaska, where
a Flood Watch is in effect for much of the region through Thursday
due to prolonged moderate to heavy rainfall. For the Bering Sea
and Aleutian Islands, gale force winds and moderate to heavy rain
are forecast from Thursday through Friday as a strong low and its
front sweep eastward across the Bering Sea. The forecast generally
remains on track, though there continues to be some uncertainty
with storm track and, thus, rain totals.

Radar this morning shows rain becoming more showery in nature
across Southwest Alaska as the front occludes and pushes further
inland with its parent low driving north towards Norton Sound
through this evening. Showers are expected to continue across
Bristol Bay and the Kuskokwim Valley through this evening as the
upper level trough pivots further east into the eastern Bering.
Overall, the general synoptic picture remains on track as this
front lingers over Southwest Alaska, followed by a North Pacific
low moving in from late Wednesday through Thursday. However, the
track of this second low is much more uncertain. There are some
differences with how far west rain will extend, with some model
guidance bringing rain as far west as Bethel, while other models
keep the rain from Wednesday/Thursday`s storm from about
Dillingham east. This will have implications for rain amounts and
flood potential for these areas. The speed of this low will also
factor into the timing of moderate to heavy rain, and whether the
Flood Watch may need to be extended to address continued moderate
to heavy rainfall after Thursday morning.

Less impactful but still notable will be nighttime lows dropping
into the low 40s and high 30s as cold air moves in behind the low
for Thursday night and Friday night. This influx of cold air will
lead to showers as the steadier rain tapers off Thursday evening,
with the potential for more robust convection due to an unstable
vertical temperature profile. The colder air may also bring a
fresh dusting of snow to taller peaks in the Western Alaska Range,
and a momentary preview of more winter-like conditions before
temperatures warm up again with the next storm.

Speaking of the next storm, the primary feature of interest for
the Bering Sea and Aleutian Islands will be a 980-990 mb low
moving in from the west for Thursday and Friday. Confidence is
high that winds will reach gale force along its front, with
moderate rain rates. The low moves across the Western and Central
Bering/Aleutians from Thursday through Saturday morning, reaching
the Pribilof and Eastern Aleutian Islands by Friday afternoon and
the Southwest Alaska coast by Saturday morning.

-JH/Chen

&&


.LONG TERM FORECAST (Friday to Tuesday)...

Rainfall from this week`s trough will be winding down though the
prolonged period of up inlet flow of precipitation could lead to
river rises especially in the Kenai Peninsula Rivers as well as
Yetna/Skwentna Rivers in the Susitna Valley through early next
week. A weak ridge builds into Southcentral Saturday evening into
Sunday morning though another round of rain is expected Sunday
through Tuesday.

A North Pacific low moves over Adak late this week and its front
brings strong winds and heavy rainfall to the Aleutians, the
Alaska Peninsula and Southwest Alaska. Wide spread small craft
advisories in the Bering Sea on Thursday increase to areas of gale
force winds, especially through the favored gap locations east of
Unalaska, Friday and Saturday. As the low moves toward the Bering
Strait, its front rotates through the Gulf of Alaska bringing
another round of heavy rain and gusty winds to Kodiak Island and
Southcentral Alaska for the holiday weekend.

&&


.AVIATION...

PANC...VFR ceilings and visibility are forecast through Thursday,
along with periods of rain through the duration. Southeasterly
Turnagain Arm winds will be common this afternoon and evening as
the first of multiple disturbances lifts across the region. In
between the first and second disturbance, winds may relax and
become down- inlet oriented later this evening. However, a second
and stronger wave of low pressure lifts across the region early
Thursday with another round of southeasterly winds, potentially
gusting into the 30 to 40 mph range during the morning hours.

BL

&&


$$