252
FXAK68 PAFC 010215
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
615 PM AKDT Sun Aug 31 2025

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

Key Messages:

 - The Flood Warning for the Yentna River in the Susitna Valley
   remains in effect until 10 AM Tuesday. Water levels for the
   river are expected to slowly decrease over the next several
   days.

 - Labor Day Weekend: Mild with a chance of light rain Sunday and Monday
   afternoons for western portions of Southcentral. Localized
   breezy areas in the afternoon and evening.

Discussion:

Currently, there is a broad ridge present in the Gulf of Alaska.
This ridge extends into the Copper River Basin, allowing for
mostly sunny skies and warmer temperatures. However, the same is
not true for Anchorage and the Mat-Su Valley. A longwave trough
over western Alaska is propelling shortwaves along the top of the
ridge. These waves are crossing into the western parts of
Southcentral from Kodiak Island to the Susitna Valley. As a
result, cloudy skies and rainfall are continuing to develop. In
particular, the Susitna Valley is expected to have on and off
rainfall today trough Tuesday. This will slow drainage of rivers
and creeks, allowing them to stay elevated. Rainfall will be more
sporadic in the Anchorage and Kenai Peninsula regions. As the
atmospheric river out west pushes into Southcentral on Tuesday,
rainfall will become more steady even in Anchorage and the Kenai
Peninsula. Wind speeds will become gusty through gap areas around
Kodiak Island. A Turnagain Arm wind in Anchorage is expected to
set up this afternoon, continuing through Tuesday as a coastal
ridge sets up from the waves.

Changes occur Tuesday as the ridge in the Gulf flattens out and
moves eastward. This will allow the trough out west to progress
eastward. This could mean another swath of rainfall moving into
Southcentral Alaska. However, there is uncertainty on how the
trough wants to move. There is agreement that it will lift
northeastward, but not on how far east it will be when it does
this. If it lifts closer to Southcentral, Anchorage, the Kenai
Peninsula, and the Mat-Su Valley could get heavy rain on
Wednesday. It it lifts more to the west, only light rain would be
possible The Copper River Basin seems to not have a good shot of
rainfall for this event. Gap winds could also become gusty around
Kodiak Island as well as Anchorage.

-JAR

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA / BERING SEA / ALEUTIANS
(Sunday to Tuesday)...

Steady rainfall and strong winds continue through late Monday in
the Aleutians, Alaska Peninsula and Southwest Alaska as a front
remains stalled over the region. A dry Tuesday morning and early
afternoon will be replaced by fast-moving system bringing rain
and wind to the area as early as the late afternoon hours.

Today`s lighter rainfall amounts will begin to increase as a wave
of heavy precipitation move northward. This heavy rainfall will
bring an additional 0.25" to 1.75" through the overnight hours to
the Pacific Ocean side of the Aleutians, from Sand Point to
Chignik, with the highest amounts in the mountains and lesser
amounts on the Bristol Bay side. These additional rainfall ranges
will be similar from Togiak to Dillingham and into interior
Southwest Alaska with the highest amounts in the mountains away
from the coastline. A second wave of heavy rain moves through
early tomorrow morning and persist into the evening hours bringing
an additional 0.75" to 2.5" to the region. The overall steering
flow during tomorrow`s rainfall will allow higher rainfall totals
to occur on the Southwest coastline with lesser amounts in the
Alaska Peninsula and Eastern Aleutians. A hydrologic outlook for
the region covers these expected rainfall totals through Monday
afternoon. The main concerns with expected rainfall will be for
higher than normal river and stream levels, as well as water
inundation and ponding of water for low-lying areas.

Wind speeds across the Bering Sea will continue to decrease into
the evening. Wind speeds and wave heights in the Alaska Peninsula
gaps, in Bristol Bay and along its coastline increase through
Monday afternoon.

A new low moves out of the North Pacific Tuesday afternoon
bringing rain and strong wind to the Eastern Aleutians, the
Alaska Peninsula and Southwest Alaska by the evening hours.

&&


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

While a stubborn ridge remains centered over the Gulf of Alaska, a
fast-transiting North Pacific low will have made its way north and
will be transitioning across the boundary between the East
Aleutian Borough and the West Aleutian Census Area by Wednesday
morning; this low will bring heavy rain with a deep moisture
fetch and gusty gap winds to the Eastern Aleutians and Alaska
Peninsula Wednesday and the Southwest Coastline, Bristol Bay to
the Kuskokwim Delta, on Thursday. A long-wave ridge will be
affecting areas further west along the Aleutians through this
period, while southcentral will remain relatively quiet with the
ridge to the south, though gusty gap winds along the Prince
William Sound and Alaska Range will be prevalent.

Once the aforementioned low breezes towards the north-Interior,
the two ridges of high pressure, which once bookended the low,
will slowly weaken, creating a messy pattern over mainland Alaska
by early Friday.

Turning west, a deep low will move out of the northwest Pacific
and extend into the western Aleutians as early as Thursday
morning, quickly becoming the prevailing driver across the
Southwest, Pribilofs and the Aleutian Chain. Meanwhile, weak
ridging will continue to prevail across Southcentral, with
chances for winds and rain ahead of the barreling low move into
Kodiak and areas north and east over the course of the day Sunday.
There are model differences as to how quickly the low will
transition out of the Pacific, into the Bering and then inland at
the end of this forecast period, which will dictate wind and rain
timing across Southern Alaska, so stay tuned for updates.

AB

&&

.AVIATION...

PANC...VFR conditions continue under mid to high ceilings through
the period. Light winds and light rain showers move through from
the southwest to start. Showers become VCSH as winds turn
southeast by 01/00Z, gain strength by 09Z, and later gust to
22 kts by 01/14Z. The Turnagain Arm winds diminish Tuesday
afternoon.

AB

&&


$$