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FXAK68 PAFC 220031
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKDT Tue Jul 21 2026

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

Key Messages:

1) A Wind Advisory has been issued from 4PM this afternoon to Noon
AKDT Thursday for the Anchorage Hillside and Upper Eagle River for
gusts up to 50 to 65 mph.

2) A Wind Advisory has been issued for the lower elevations of
Eagle River, Anchorage, and Eklutna from 1AM AKDT Thursday to Noon
AKDT Thursday for expected gusts of 30 to 45 mph.

3) A Wind Advisory has been issued for the Western Kenai
Peninsula along and near Cook Inlet for wind gusts of 35 to 50
mph. 8 to 12 feet waves expected moving northward up the Cook
Inlet.

4) Flood Advisories remain in effect for the Yentna and Skwentna
rivers.

5) Flood Watches remain in effect for the Susitna Valley and
Hatcher Pass due to excessive rainfall and continuing into mid
week.


Discussion:

A wet, windy, and dynamic forecast remains on track for
Southcentral Alaska. Looking at 500 mb model analysis, the general
setup through Wednesday morning is that of a negatively tilted
longwave trough draped from the Bering Strait to the northern
Gulf, with weak vorticity lobes/waves embedded within the mean
flow. Currently, radar returns show rain filling in from southwest
to northeast across the Cook Inlet region. Also at the surface,
coastal ridging will continue to build through this evening across
the Gulf coast, setting up an east to west pressure gradient from
Whittier to Anchorage, thus inducing a southeasterly Turnagain
Arm wind. Although the core of the strongest winds will likely
stay over the Arm, a negative pressure gradient from Anchorage to
Homer will bend some of these winds into the Anchorage Bowl,
creating breezy conditions as rainfall continues to overspread the
region, with stronger winds for the Anchorage Hillside. Thus, an
impact based Wind Advisory has been issued for a combination of
elevated winds and saturated soils that could cause downed trees
for the Anchorage Hillside. Hi-res model guidance is hinting at
gusts approaching 50 mph for the Hillsides.

By early Wednesday morning, a weak surface trough/low crosses the
Alaska Peninsula and into the northern Gulf, bringing additional
rainfall to coastal areas. At the same time, the 500 mb longwave
trough is lifting northward and exiting the region. This will
cause steady rain to taper to showers across most of Southcentral
with the exception of coastal areas like Seward, Chenega, Valdez,
and Cordova. Albeit weak, the surface feature will help to flatten
the coastal ridge situated across the eastern Gulf and coastal
Southcentral, allowing winds to decrease (but remain breezy)
across Anchorage for a time Wednesday morning. A brief lull in
rainfall is also expected late Wednesday morning as Southcentral
becomes sandwiched in between storm systems. Through Wednesday
afternoon, most locations across the Cook Inlet region are on
track to see an additional 0.25 to 0.50 inch of rainfall, with
higher values for the Eastern Kenai Mountains with upslope
enhancement.

Starting late Wednesday morning to Wednesday afternoon, the
surface low exits the region to the south and moves inland over
the Alaska Panhandle, which will allow for a redevelopment of a
coastal ridge and southeasterly Turnagain Arm winds. All of the
guidance suggests this will be a stronger and more dynamic system
than the one ongoing. Diving into the details of Wednesday
afternoon`s system, the first component is a deeper low pressure
system moving inland from the northern Bering Sea and into the
north-central part of the state. Its front is on track to sweep
across Southwest Alaska through Wednesday evening. Aloft, the
global models shows that its associated shortwave trough/closed
low will be robust, and a leading upper trough will move over
Southcentral first midday Wednesday. A combination of lowering
pressure ahead of the front, the reformation of the coastal ridge,
and the overall synoptic flow will lead to enhanced wind speeds
with this system...not just through the Turnagain Arm, but for the
Cook Inlet and Knik River Valley as well. Some of these winds
will most likely make it as far inland as the Matanuska Valley,
but will be much weaker than for gaps to the south and east. For
the Cook Inlet, reinforced up-inlet flow with gales is likely
Thursday morning. Although the bulk of these winds will stay
offshore, places like Kenai Beach could very well end up being
clipped with these winds as well as Nikiski (and places where the
western Kenai Peninsula coast juts out into the Inlet). These
winds will lead to high seas up to 12 feet or so moving north up
the Inlet. Therefore, a Wind Advisory has been issued for the
western Kenai Peninsula, with an emphasis on the western coastline
seeing the strongest of these winds (gusts to 50 mph).

Regarding rainfall, one area of concern is a period of heavy rain
(Wednesday night into Thursday morning) in the Talkeetna
Mountains and nearby portions of the Matanuska and Susitna Valley
resulting in fast responding rivers and streams such as the Little
Susitna River and Willow Creek to be susceptible to flooding.
Larger and slower responding rivers across the Susitna Valley will
also see fairly heavy rain and will not have a chance to drop
much this week, so out of bank flooding onto floodplains is also
likely for some of these locations. For Thursday morning, the
concern for stronger winds and downed trees grows as low level
convergence sets up as up-inlet gales interact with the Turnagain
Arm wind, leading to enhanced precipitation and QPF. With this
additional forcing, pouring rain Thursday morning on the tail end
of the system working in tandem with strong winds across the
Anchorage area increases the likelihood of downed trees from
saturated soils from recent and ongoing rainfall. Through Thursday
night, most locations across the Cook Inlet region will see
another 0.25 to 0.50 inch of rainfall, with higher values for
western slopes of the Talkeetna Mountains due to the synoptic flow
shift between systems. Wind wise, the 850 mb cold air
advection/instability with this system is quite impressive, and
vertical momentum transport from sinking air aloft will lead to
stronger wind gusts making it to the surface Thursday morning.
Starting Friday morning, conditions begin to improve in regards to
both rain chances and wind.


-AM/KC

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Days 1 through 3: Today through Friday)...

A low has pushed onshore over the Kuskokwim Delta Coast. The next
low is not far behind and is currently over the Bering Sea north
of Shemya. Rain across the Kuskokwim Delta Coast, Bristol Bay
Coast, and Alaska Peninsula (AKPEN) will slowly taper off as the
regions move in between these systems. The same is true with the
southerly to southeast gusty winds (of 15 to 25 mph) blowing over
Bristol Bay and south of the Alaska Peninsula; they will slowly
diminish through tonight.

Winds turn southwesterly through this tonight along the waters of
Bristol Bay and Mainland Bristol Bay. Wave heights of 4 to 7 feet
in the coastal waters of Kuskokwim Bay will slowly subside
through the rest of the day. For Bristol Bay, wave heights of 7
to 10 feet will slowly subside this evening into early Wednesday.
However, this subsiding of wave heights will not last long as our
next system approaches.

Attention then turns to the aforementioned low over the Bering Sea
quickly approaching on the heels of today`s low. Its front is
spreading warm air and rain over the Shemya area. Rain then moves
east to Adak/Atka and the Pribilof Islands by late tonight into
early Wednesday morning. The system continues to deepen as it
moves just west of Saint Matthew Island late Wednesday morning. By
this time, a surge of warm air and moderate to heavy rain
associated with the front will have begun to move over coastal
Southwest Alaska. Moderate to heavy rain then moves inland across
the rest of Southwest through Wednesday afternoon and Wednesday
night. The heaviest rain with this system will occur farther north
than with today`s system. The heaviest rain is expected to fall
across the Kuskokwim Delta, Kuskokwim Valley, and along the
Western Alaska Range. Expect 1 to 2 inches of rainfall from this
system from Wednesday morning into Thursday morning for the
Kuskokwim Delta, Kuskokwim Valley, and Western Alaska Range. The
Western Alaska Range will see the higher-end totals due to
favorable upslope southwesterly flow. For Bristol Bay and the
AKPEN, expect 0.50 to 1 inch of rainfall Wednesday morning into
Thursday morning. The higher-end totals here will also occur
inland with the favorable southwesterly upslope flow along the
Western Alaska Range and Northern Aleutian Range.

Likewise with today`s system, gusty winds, from the south and
southwest, will make it over the Kuskokwim Delta and Northern
Bristol Bay Coasts by Wednesday morning. Gale-force winds will
also occur over the coastal waters of the Kuskokwim Delta and
Northern Bristol Bay. Expect wave heights to build along the
coastal waters of Kuskokwim and Bristol Bays through Wednesday
evening. Peak wave heights along Kuskokwim Bay will be 8 to 14
feet with 9 to 13 feet likely for Bristol Bay. Wave heights will
slowly subside through Thursday. A Special Weather Statement has
been issued through Thursday for the Kuskokwim Delta Coast, the
Western Capes, and the Northern Bristol Bay Coast to bring further
awareness to the heavy rain, gusty winds, and rough seas along
the coastal waters with the next low set to impact the area.

As mentioned above, scattered rain showers will continue across
Mainland Southwest through Thursday as the AKPEN begins to dry
out by late Thursday morning into Thursday afternoon. Meanwhile,
another round of rain and warm tropical air makes it way to the
Aleutians Wednesday evening through Thursday. The North Pacific
ridge builds farther north over the Central and Eastern Aleutians,
so Adak/Atka and Nikolski/Unalaska/Akutan should remain mostly
dry by Friday. Some moisture makes it around the northern
precipice of the ridge and across the Bering to the Pribilofs and
southern AKPEN for Friday. Otherwise, except for some lingering
showers along the mountain ranges, Southwest looks to finally dry
out for Friday.

DAN/JAR

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through
Tuesday)...

By Saturday morning, high pressure is expected to remain
stationed over the southern and eastern Bering Sea, with a
weakening low pressure system in the northern Gulf of Alaska.
Through the remainder of the weekend, the ridge over the Bering
appears to remain relatively stationary, with the weak trough over
the Gulf dissipating, leaving a fairly undefined set-up over
Southcentral. The lack of defining features in the Southcentral
area may result in heightened local effects given the weak
synoptic flow pattern. In the Bering, ridging may promote either
clear skies and/or widespread low stratus. By Tuesday morning, the
ridge in the Bering appears to begin shifting south out of the
area, which may allow for more active features to make their way
in eventually, but ultimately leaving the Bering and the southern
mainland in zonal flow for most of Tuesday.

-CL

&&



.AVIATION...

PANC...An approaching upper level short-wave and surface front
will bring another round of rain and gusty southeasterly winds
this afternoon through tonight. The primary area of uncertainty
is in the ceiling forecast. The southeasterly low level winds
are favorable for maintaining VFR ceilings. Working against this
will be the flow from around 5000 feet on up, which starts out
southerly and backs to the southwest as the short-wave comes
through overnight tonight. This does tend to favor lower ceilings.
Thus, there could be a period of MVFR ceilings - mostly likely
overnight through early Thursday morning.

Winds will weaken Wednesday morning, but will likely remain gusty.
There will be a brief break in rain before a stronger storm system
approaches later in the day, with rain and gusty southeast winds
redeveloping Wednesday afternoon and intensifying Wednesday evening.
Low level southeast flow looks shallower (with deeper and moister
southwest flow aloft), so confidence is higher that ceilings will
fall to MVFR Wednesday afternoon.

-SEB

&&


$$