419
FXAK68 PAFC 290126
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
526 PM AKDT Thu Aug 28 2025

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

Key messages:

 - An atmospheric river continues to move across Southcentral this
   evening. Flood Watches remain in effect for the eastern Kenai
   Peninsula and the Susitna Valley. A Flood Warning is now in
   effect for the Yentna River above Lake Creek.

 - Strong gap winds into the Mat Valley, Anchorage and Copper
   Basin are peaking or have already peaked this afternoon. A High
   Wind Warning remains in effect for the Anchorage Hillside,
   Anchorage Bowl, and Matanuska Valley (Palmer and Butte) through
   this evening. A Special Weather Statement is out for portions
   of the Copper River Basin and Copper River Valley.

 - Rain and strong winds will end from west to east late tonight
   into Friday as quieter conditions return for the start of the
   weekend.

Discussion:

A very active pattern remains in place across Southcentral this
afternoon as an atmospheric river and strong frontal system
continues to bring a range of impacts from strong winds to very
heavy rainfall to the area. The ongoing high winds across
Anchorage, the Matanuska Valley and through the Copper River Basin
have most likely already reached their peak already earlier this
afternoon, but strong to damaging wind gusts will remain possible
until winds begin to diminish more quickly later this evening,
namely near Palmer and across parts of Anchorage. Taking a broader
look at the synoptic picture, the main upper trough situated over
Southwest Alaska is now beginning to lift up towards the Alaska
Range, with a cold front now stretching from an elongated surface
low moving up into the Kuskokwim Valley south to Kodiak Island.
Bands of moderate to heavy rainfall continue to stream into the
Cook Inlet, Mat-Su and Kenai Peninsula out ahead of the trough and
front, particularly where southerly flow is upsloping into
terrain near the Alaska Range and from portions of the Prince
William Sound to the southern Kenai Peninsula. Rises have already
been observed on a number of waterways, particularly along parts
of the Yentna River, where a Flood Warning is now in effect
through Sunday.

Overall, the forecast from tonight onwards remains on track. The
main upper trough off to the west will amplify and accelerate
northeast into the Copper River Basin by Friday afternoon, while
the main moisture tap and front sweep across Southcentral from
west to east. Cooler, drier air will advect into the region with
the frontal passage, and the worst of the gap winds should also
begin to diminish from late tonight into Friday morning. One
exception will be across portions of the western Kenai Peninsula,
where a combination of pressure rises behind the frontal passage
and cold air advection through the Kamishak Gap will usher strong
southwesterly winds up the Cook Inlet beginning late tonight and
persisting into much of Friday. Gusts of 30 to 45 mph are not out
of the question from Homer north to Kenai, especially early on
Friday morning. Gusty southwesterly winds will also develop over
at least West Anchorage through Friday evening. Periods of rain
will end from west to east through Friday evening as the front and
upper trough progress steadily northeast with time. Ahead of the
trough passage, cooling air aloft coupled with daytime heating
over the Copper Basin could yield a few thunderstorms on Friday
afternoon as the air mass briefly becomes more unstable.

Behind this system, expect clearing skies by Friday afternoon and
evening. Low temperatures overnight Friday into early Saturday
morning could dip into the 30s for some sheltered locations if
winds become calm. Saturday again looks to be much calmer and
quieter as the upper level ridge rebounds overhead. Cloud cover
and rain chances will begin to increase somewhat from late
Saturday into Sunday ahead of a strong low pressure and frontal
system moving over Southwest. Right now, it looks like the best
rainfall chances will stay confined to the Alaska Range and
northern Susitna Valley, but this will depend on how far the front
along with a returning moisture axis is able to work into
Southcentral through Sunday evening.

-AS/TM

&&


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

Longwave troughing extends across portions of Southwest Alaska
through the rest of this evening. Light rain will gradually fizzle
out through this evening, with drier conditions expected for much
of Friday. A colder airmass will quickly track west to east
across Southwest Alaska, allowing temperatures to drop into the
upper 30`s tonight.

Farther west, high pressure is set up over the southern Bering
Sea and Aleutian Islands. Widespread low stratus will continue
Friday as the ridge tracks eastward. A front extending off a
Kamchatka low moves over the Western Aleutians this afternoon and
will track eastward over the next couple of days. Widespread
rainfall and gale force winds are expected along the front. There
will be an area of storm force gusts along the front as it passes
over the Western/Central Aleutians before diminishing back to gale
force gusts as it pushes over the Eastern Aleutians. The front
reaches Southwest Alaska early Saturday morning. Another round of
rainfall will impact the Kuskokwim Delta and Western Capes
initially on Saturday morning before becoming more widespread
across Southwest Alaska by late Saturday evening. Persistent
southerly flow along the northern Kuskokwim Bay may produce areas
of increased surf at times, the chance for coastal flooding
remains low at this time but will continue to be monitored.

&&


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

At the beginning of next week, a broad longwave trough will be
situated over the western and central Bering Sea, while a longwave
ridge extends up from the North Pacific into the Gulf of Alaska
toward the Alcan Border. This general pattern looks to hold
through mid-to-late week, aiming a stream of tropical moisture in
excess of one inch of precipitable water between these features,
toward the Alaska Peninsula and Southwest Alaska. As a result,
several inches of rainfall are forecast along the Pacific side of
the Alaska Peninsula, potentially in excess of 4 inches for some
locations through Thursday. Lower amounts, broadly speaking 1 to 3
inches are possible for mainland Southwest Alaska. While these
regions are likely to be wet for much of the long term forecast
period, there is uncertainty in the exact orientation of the
atmospheric river, so many locations will likely see several
periods of moderate to heavy rain as the moisture plume wobbles
back and forth (west/east). There is some potential that the moist
southerly flow glances parts of Southcentral, with the Cook Inlet
region and southern Kenai Peninsula with the greatest potential
to see another round of lighter rainfall.

Otherwise, gusty southerly winds from a broad, weakening low
tracking into the northern Bering Sea on Sunday will lead to a low
risk of coastal flooding along the northern Kuskokwim Bay
coastline. Winds decrease on Monday as the low lifts into the
Bering Strait or across the far eastern reaches of Chukotka. High
pressure across the Gulf of Alaska keeps winds light and
conditions generally dry across Southcentral for the duration of
the forecast period (with the exception of the aforementioned
potential for glances of moisture intrusion). By Wednesday, the
next North Pacific low approaches the western Aleutians, bringing
gusty winds, potentially to gale force, and light to moderate
rainfall. The track of this low is particularly uncertain, but it
looks to be fairly slow moving and generally tracks along the
periphery of the Aleutian Chain through the end of the week.

&&


.AVIATION...

PANC...Southeast winds are expected to continue this evening with
gusts up to 50 kts possible. Although winds should start to
decrease tonight, they will shift more southwesterly by Friday
morning and gustiness of 20 to 30 kts is expected to continue
until later Friday afternoon and evening.

Downslope drying is expected to end later this evening as
southwest flow from Cook Inlet along with a front tries to push
eastward over the terminal. Although the onset timing of the
rainfall is of lower confidence, rainfall is certainly expected to
return tonight through Friday morning. VFR conditions is expected
with drips into MVFR within heavier showers overnight and Friday
morning.


&&


$$