NWS Anchorage, AK wrote its last area forecast discussion before the first event at Aug 27, 4:04 PM AKST, 8 hours 56 minutes earlier.
Area forecast discussion, Aug 27, 4:04 PM AKST, 8 hours 56 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
504 PM AKDT Wed Aug 27 2025
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
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 on Thursday. A High
Wind Warning is now in effect for both the Anchorage Hillside
and Anchorage Bowl beginning early on Friday.
- Rain and strong winds will end from west to east from Thursday
night into Friday as quieter conditions return for the start of
the weekend.
Discussion:
Radar and satellite imagery this afternoon are now highlighting
the next shortwave moving up along the western Alaska Range into
the Cook Inlet and Mat-Su Valleys, and the associated batch of
light to moderate rain has now overspread the western half of
Southcentral. 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 1.5" precipitable
water values now beginning to work up into the mouth of the Cook
Inlet ahead of the frontal zone sitting off to the west. A new low
is rapidly developing south of the Alaska Peninsula near a more
pronounced shortwave trough rounding the base of the broader
trough out west, and this new feature will become a key focal
point in the forecast over the course of the next day or so.
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 on Thursday
morning and reaching the western Interior by Thursday evening.
Gap winds ongoing near Anchorage and Palmer will relax markedly
this evening as a down-inlet gradient develops 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 70 mph gusts possible across the
Anchorage Hillside starting early Thursday and lasting through
much of the day. Please see the High Wind Warnings in effect for
Anchorage and the Special Weather Statement in effect for the Mat
Valley for additional details on winds expected through Thursday
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
been lowered slightly across the northern Kenai Peninsula and
Anchorage area given a 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 from Friday morning through Friday
night, with some clearing even likely by the late afternoon and
evening. Saturday again looks to be much calmer and quieter as the
upper level ridge rebounds overhead.
-AS
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Tonight through Saturday)...
Southwest Alaska experienced a brief lull in active weather today
as precipitation became more showery and sparse in coverage with
an upper-level shortwave ejecting north and east into the
Interior. A weak frontal boundary persists, however, stretching
across the Alaska Peninsula, Bristol Bay, and the Western Alaska
Range this afternoon. It is along this frontal boundary which a
compact North Pacific low, currently located several hundred miles
south of the Alaska Peninsula, quickly lifts north tonight. Ahead
of the low, tropical moisture, with precipitable water values in
excess of one inch, will overspread the peninsula and into
Southwest Alaska late this evening, leading to another round of
moderate to heavy rain. Increased model agreement lends increased
confidence that the bulk of this precipitation will fall east of a
line roughly extending from King Cove north to Togiak and finally
to Aniak. As a result, the Flood Watch has been canceled for the
interior Kuskokwim Delta and the Western Capes, while it remains
in effect for Bristol Bay and parts of the Lower Kuskokwim Valley.
These areas are likely to see between one and two additional
inches of rainfall through Thursday as the low lifts across
Southwest Alaska.
Behind the low Thursday night, cold air spreads in across
Southwest Alaska from the northern Bering Sea. This will bring
nighttime lows into the low 40s to upper 30s, aided by mostly
clear skies. 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 beginning on Thursday. 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...Breezy southerly winds will persist throughout the TAF
period for Anchorage, with the strongest winds expected this
evening as the coastal ridge strengthens, thus increasing the
pressure gradient. Conditions will remain VFR otherwise.
&&