NWS Anchorage, AK wrote its last area forecast discussion before the first event at Aug 28, 3:55 AM AKST, 10 hours 5 minutes earlier.
Area forecast discussion, Aug 28, 3:55 AM AKST, 10 hours 5 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 AM AKDT Thu Aug 28 2025
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
No significant changes to the previous forecast discussion.
Key messages:
- An atmospheric river and frontal system is slated to bring
widespread rainfall across much of Southcentral through Friday
morning. Flood Watches are now in effect for the eastern Kenai
Peninsula and the Susitna Valley.
- Strong gap winds into the Mat Valley, Anchorage and Copper
Basin are expected to peak during the day today. A High Wind
Warning remains in effect for the Anchorage Hillside, Anchorage
Bowl, and Matanuska Valley (Palmer and Butte) through tonight.
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.
Synopsis:
Radar and satellite imagery this morning show a potent shortwave
and surface low driving into Southwest Alaska. This shortwave is
one of several riding in between a longwave trough over the Bering
Sea and a strong upper ridge extending from the Gulf into much of
Canada. A slow moving cold front and attendant atmospheric river
are continuing to make slow but steady eastward progress, with an
axis of 1.0" to 1.5" precipitable water values pushing up Cook
Inlet and into Prince William Sound. Gap winds, along with winds
at ridge-top level, are both rapidly increasing this morning.
Gusts to 60 mph have already been observed along the Anchorage
Hillside with gusts over 75 mph at mountaintop locations above
3,500 ft. Southeasterly winds through Turnagain Arm are also on
the increase and are beginning to clip the far western portions of
the Anchorage Bowl, with gusts to 25 mph. Intermittent wind gusts
have also been reported at Palmer.
Steady rain continued to fall across the western half of
Southcentral, with pockets of heavy rain over the Kenai Peninsula
this morning where half an inch or so of rain has already fallen.
Farther north, overnight totals are slightly less across the
Anchorage Bowl, around a quarter of an inch. However, upwards of
three quarters of an inch has fallen over the Susitna Valley.
Discussion:
Much of the forecast remains on track by and large. The most
notable short-term change has been to further increase the peak
winds expected through the various gaps of note, including across
Anchorage, the Mat Valley and across the Copper River Basin. The
new low currently developing south of the AKPen is still poised to
move very quickly north along the front stretching northeast out
ahead of the center, speeding up through Southwest this morning
and reaching the western Interior by this evening. Gap winds
near Anchorage and Palmer will fluctuate as a down-inlet gradient
tries to hold on out ahead of the approaching low, but will roar
back in with even more intensity as the low moves north and
effectively tugs winds back towards the north. In addition to the
impressive mid to upper jet supporting this system, models have
trended stronger with a roughly 60 kt southeasterly low level jet
expected to develop ahead of the front and approaching low across
the Kenai Peninsula and Cook Inlet region. Confidence has
increased for gusts ranging from 30 to 55 mph to occur at the peak
of the event across the Anchorage Bowl and Mat Valley, with up to
75 mph gusts possible across the Anchorage Hillside starting
early this morning and lasting through much of the day. While low
confidence, there is even a small chance for an isolated gust or
two to 80 mph on the hillside and up to 60 mph for both W and NE
Anchorage and near Palmer. Please see the High Wind Warnings in
effect for Anchorage and Palmer and the Special Weather Statement
in effect for the Copper River Basin for additional details on
winds expected through this evening.
The other important aspect of this system will be rainfall.
Moisture advection will increase markedly into Southcentral as
both winds aloft and near the surface ramp up tonight along a
tropical moisture tap already beginning to move into the southern
tip of the Kenai Peninsula. General thinking for precipitation
totals through Friday morning remains on track, with the heaviest
rainfall totals ranging from 2 to 5 inches focused where there
will be the greatest upslope enhancement across the western Kenai
Peninsula and Prince William Sound, as well as along the Alaska
Range out to the northern Susitna Valley. Rainfall totals have
again been lowered slightly across the northern Kenai Peninsula
and Anchorage area given a continued downward trend in model
projections that's likely associated with the strengthening trend
in low level, downsloping southeasterlies on the front end of this
system. Flood Watches are now in effect where the highest
rainfall totals and possible flooding concerns are highest through
Friday morning, across much of the Susitna Valley and towards the
southeastern Kenai Peninsula. See the Flood Watch and Hydrologic
Outlooks currently in effect for additional details.
A trend towards much quieter conditions will begin on Friday as a
secondary shortwave embedded in the western trough phases with the
shortwave moving up into the western Alaska Range, pushing the
cold front and moisture axis northeast as the trough aloft
accelerates in the same direction. Gap winds and rain will sharply
drop off from west to east; however, strong cold air advection
aloft along with pressure rises will allow for gusty southwesterly
winds to develop up Cook Inlet for Friday morning and afternoon.
Gusts of 30 to 45 mph are not out of the question from Homer north
to Kenai. Gusty southwesterly winds will also develop over at
least West Anchorage through Friday evening.
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.
-AS/TM
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Tonight through Saturday)...
Another round of moderate to heavy rainfall across Southwest
Alaska is underway this morning as a North Pacific low lifts along
the frontal boundary which remains situated across the Alaska
Peninsula, Bristol Bay, and the Western Alaska Range. While the
main axis of moisture continues to pivot east into the Gulf of
Alaska, precipitable water values in excess of one inch ahead of
the low continue to stream into Southwest Alaska and promote one
more round of widespread rainfall to conclude this week's long-
duration rainfall event. As the low approaches the southern AKPen
this morning and takes a northeasterly track along the Alaska
Range, the bulk of the precipitation will fall east of a line
roughly extending from Nelson Lagoon to Dillingham up to
Sleetmute. Areas further west from Togiak to Aniak will continue
to see modest rainfall amounts through this morning before the
system progresses eastwards as the upper level trough axis finally
begins to push across the region. A Flood Watch remains in effect
through this morning for Bristol Bay and parts of the Lower
Kuskokwim Valley as the eastern portions of these areas are likely
to see between 1 to 1.5 additional inches of rain through this
afternoon.
Cold air spreading across the region tonight behind the departing
low and clearing skies will allow temperatures to fall into the
upper 30s to low 40s across much of Southwest Alaska. The colder
air may also bring a fresh dusting of snow to higher elevations of
the Kilbuck and Ahklun Mountains, as well as some of the
foothills of the Western Alaska Range. Southwest Alaska
experiences a break in active weather on Friday, with only a
chance of rain showers forecast.
For the Bering Sea and Aleutian Islands, A North Pacific low
brings gale force winds and moderate to heavy rain to the western
Aleutians and Bering Sea beginning this afternoon. The low tracks
across the western Aleutians on Friday, pushing its front to the
central Aleutians and then to the eastern Aleutians/Alaska
Peninsula by Saturday. Friday night into Saturday, the front
begins to move onshore of the Southwest Alaska coast, which begins
the next round of wet weather for the region. Tides are forecast
to be low amplitude this weekend, so the strong southerly winds
are not likely to induce coastal flooding issues at this time.
&&
.LONG TERM FORECAST (Saturday to Wednesday)...
The long range forecast is characterized by a continued
atmospheric river in Southwest Alaska and a ridge building in the
Gulf of Alaska. The atmospheric river will allow for steady
rainfall spanning from the eastern Aleutians/Alaska Peninsula to
inland areas including the Lower Kuskokwim Valley all the way
through Wednesday. There is uncertainty for the placement of the
plume of moisture, so the area that is forecasted to receive the
most rainfall could change. Other than that, gusty winds will
again be possible for the Southwest coastline on Saturday as a low
pushes in from the west. Winds drop off as the low moves
northeast of the region and weakens. High pressure will build in
afterwards on Monday, keeping wind speeds down for the forecast
period.
For Southcentral, it is more uncertain. A ridge of high pressure
will build into the Gulf of Alaska on Saturday, dropping off wind
speeds and rain chances for the Gulf and Kodiak Island. Inland
areas will also see their rain chances drop off and wind speeds
die down. However, there is some uncertainty in the exact size and
position of the ridge. Some guidance has it shorter and further
south, allowing shortwaves to continue moving into inland areas of
Southcentral. This would cause rain chances and wind speeds to
remain elevated. However, other guidance has the ridge stronger
and further north, which would keep rain chances and wind speeds
low for inland areas of Southcentral. Continue to monitor the
forecast for future updates.
-JAR
&&
.AVIATION...
PANC...Light northerly winds are anticipated early this morning
with gusty southeast winds aloft. Thus, a period of low-level
windshear is likely before flow throughout the atmosphere becomes
predominately south to southeast. That said, there may be times
early this morning when southeasterly gusts out of Turnagain Arm
clip the terminal, counteracting the predominant northerly down
inlet flow.
The strong gusty southeasterly winds out of Turnagain Arm will
then take hold by mid to late morning and continue through late
this evening. Peak wind gusts could reach up to 40 kts at times
during the late morning to early afternoon hours today. Gusts then
slowly diminish to 25 kts through late evening with flow then
turning south to south-southwest tonight through Friday morning.
As flow turns southwesterly, a resurgence of gusty conditions,
peaking around 30 kts, is likely Friday morning and afternoon with
colder and unstable air moving in behind the departing storm
system.
Looking into the precipitation forecast for today and tonight,
showers are likely across the terminal early this morning. Showers
become more sporadic in nature late morning as stronger
southeasterly downslope flow takes hold. As flow turns more
southerly to south-southwesterly tonight, another round of
steadier showers is possible before things dry out Friday morning.
While conditions are expected to remain VFR, thanks in part to
the strong southeasterly flow initially, cloud ceilings could
still drop to 5,000 feet at times through the TAF period. A lower
scattered deck, around 2,500 to 3,000 feet, may also develop at
times; especially early this morning and tonight.
&&