008
FXAK68 PAFC 210254
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
654 PM AKDT Tue May 20 2025

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

A southerly flow regime has become established across Southcentral
between a longwave trough extending from the western Arctic Ocean down
into the eastern Bering Sea and a longwave ridge extending across
Northwest Canada and AlCan Border. A couple weak shortwaves are
lifting north within this broad region of southerlies, one in the
eastern Copper Basin, and another near the Mat-Su Valleys.
Isolated to scattered showers have once again developed with
pockets of afternoon sunshine and heating, namely over the western
Kenai Peninsula, Mat-Su Valleys and northern Copper Basin. A
couple more lightning strikes will still be possible near the
northern Alaska Range and across the Mat-Su this evening. However,
the cooler air streaming in from the Gulf today has helped keep
instability more limited overall compared to yesterday. Thus, any
thunderstorm activity through this evening will remain very
isolated in nature.

On Wednesday, a potent shortwave trough and attendant low will
move into the Gulf just to the south of Kodiak Island. This low
will push its front into the central and western Gulf, spreading
gusty southeasterly winds and rain into Kodiak Island and up into
the eastern Kenai Peninsula. The approaching low and front over
the Gulf will help build up a coastal ridge along the north Gulf
Coast, and this should drive fairly potent gap winds through the
Turnagain Arm, Knik Valley and Copper River Valley during the
afternoon and evening. Southeasterly gusts up to 30 to 40 mph
will be common along parts of the Turnagain Arm, as well as parts
of the Anchorage Hillside and western side of the Anchorage Bowl.
Similar or slightly weaker winds are expected across parts of the
Mat Valley and Copper River Basin. While it will certainly be a
blustery day in places, the interior valleys should stay fairly
dry thanks to the strong southeasterly flow developing north of
the Gulf low/front and downslope drying in the lee of the
mountains.

From Thursday into Friday, a transition to a quieter, warmer and
drier pattern will begin as the Gulf low moves off into the
Northeast Pacific and as prevailing winds aloft begin to turn more
easterly to northeasterly. This should draw warmer and drier air
into Southcentral from the Interior and Yukon, especially on
Friday. It`s looking like quite a pleasant close out to the work
week on Friday afternoon, with increasingly clear skies and a
decent chance for valley temperatures to approach or exceed 60
degrees Fahrenheit.

&&


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

Currently, scattered showers are forming across the Southwest
Alaska mainland as a low over the Alaska Peninsula moves eastward.
Wind speeds are relatively light and easterly in the mainland.
The Eastern Aleutians are a different story. They are seeing heavy
rains and gusty galeforce northwesterly winds, especially out of
gap regions. The western Aleutians are under a ridge and are
relatively calm with scattered showers. As the low continues its
trek eastward on Wednesday, the main core of precipitation will
move over the mainland, allowing for more widespread rains and
gusty easterly winds out of the Kamishak Gap into Bristol Bay. The
Bering will see a weaker low push a front into the western
Aleutians by Wednesday afternoon, allowing for another round of
precipitation and small craft winds. This low will quickly weaken
and phase into the first low by Thursday. It will drag an area of
light precipitation and winds into the Fox Islands on Thursday
before this happens.

The first low will push into the Gulf of Alaska by Thursday, and
higher pressure will build into the southwest mainland, allowing
for drier and calmer conditions through Friday. Although,
lingering showers are still possible in the Lower Kuskokwim Delta.
Also, gusty winds out of the Kamishak Gap will also linger
through Friday morning. The Bering will have a broad ridge set up,
allowing for calmer and less rainy conditions. However, this
ridge will quickly be pushed southeastward by a strong Kamchatka
low from the west. A strong front from the low marches through the
Aleutians, arriving at the Fox and Pribilof Islands by Friday
night/Saturday morning. Gale force winds and heavy rains will be
associated this front.

-JAR

&&



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

A number of upper level low centers progress from the Russian Far
East across the Bering and Alaska Peninsula into the Gulf of
Alaska through the forecast period. Main jetstream energy remains
across the North Pacific into the new week, with shortwaves
passing through the pattern. Most of the active weather will be
occurring over the Southern portions of the state. Ensemble
forecast models handle the features overall with some variations
in timing of individual events.

Lingering showers are expected over the Southern half of Mainland
Alaska through the weekend. A well developed low and front
pushing across the Western Aleutians and Bering brings moderate
rain and locally gusty winds across the region. This front moves
over the Central and Eastern Bering on into Western Alaska, the
AKPEN and Kodiak Island Sunday before spreading across
Southcentral Alaska through Tuesday. Locally moderate rain moves
further into the Interior with the front extending across the
coasts. The supporting surface low crosses the AKPEN Monday and
slips South of Kodiak Island through Tuesday.

- Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the period. The
Turnagain Arm wind will continue to bend over the terminal this
evening, slowly decreasing through the overnight hours. Thursday
looks to be a scenario where the wind is not necessarily bending
over the terminal, but where the wind is only clipping the
airport, coming straight out of Turnagain Arm.

MTL

&&


$$

913
FXAK67 PAJK 210534 AAA
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
930 PM AKDT Tue May 20 2025

.SHORT TERM...Somewhat dreary day, with a nearly fully saturated
atmosphere for the panhandle from the surface up to 500 mb. A
weak, progressive shortwave aloft moving over the panhandle looks
to provide the most modest amount of lift to ensure most areas of
the panhandle remain wet for this Tuesday. Looking at water vapor
satellite, a dry slot in the southern panhandle is clearing some
clouds in Ketchikan with mostly clear conditions in the Metlakatla
area. Wednesday sees the weak shortwave be replaced by a transient
ridge aloft, which will provide some clearing from dry air
advecting into the inner channels, but due to widespread surface
moisture, not looking to see widespread clear skies.

.LONG TERM...Looking towards late week, guidance have begun to
converge on a less progressive pattern, with increased cold air
descending down from the Arctic. This cold air will intensify the
trough, increasing the amplitude, and directing the moisture flow
towards SE AK. The result will be multiple waves of moisture
moving over the panhandle beginning this Saturday. Exact details
of this evolving system are hazy, but what can be said is long
duration moderate rain with periods of heavy rain will move into
the southern panhandle. What is uncertain is how far this moderate
to heavy rain producing moisture will move northward. Currently,
the more likely solution is the heavier moisture will be directed
at the southern panhandle with lighter precipitation from
Petersburg up to Juneau. However, trends in ensemble guidance has
probabilities increasing for these much higher than normal
precipitation totals up into the Juneau area. In the southern
panhandle, there is around an 80% chance for 2 inches of rainfall
in 24 hours, while the same percentage chance exists for 1 inch of
rainfall for areas like Juneau, Gustavus, Angoon, and Sitka.
Regardless of either solution, with the current state of rivers,
no flooding is currently expected.

&&

.AVIATION...Mainly VFR ceilings and vis this evening with some
scattered areas of MVFR ceilings down to 1600 ft here and there this
evening. The showers across the southern panhandle have diminished
from what they were this afternoon, but they are still bringing some
ceilings down to 2500 ft and vis down to 5 miles at times mainly
over Wrangell and Misty Fjords. Some MVFR ceilings are possible
after midnight tonight as lower marine layer clouds develop, but
most places should then improve to VFR by mid to late morning with
showers continuing here and there through Wednesday night at least.
Winds remain less then 15 kt for most areas but Skagway may remain
the exception to that with 15 to 20 kt winds possible there through
Wednesday evening.

&&

.MARINE...

Eastern Gulf of Alaska: Surface ridging over the
panhandle will give general onshore-to-southerly flow in the Gulf.
Wind speeds will be generally 5 to 15 knots through Thursday,
little closer to 15 to 20 knots in the central gulf. Friday into
Saturday, an area of low pressure will track southeast through the
western and southern gulf. Ahead of this low, southerly wind
speeds will increase to around 15 to 25 kts with the higher
speeds, 20 to 25 knots, in the southern marine areas and in Dixon
Entrance.

Wave heights will be mainly less than 5 feet until that low pressure
approaches, then wave heights will build ahead of the low to upwards
of 8 to 10 feet.

Inner channels: Inner channel wind speeds look to be pretty light
overall through most of Friday - generally out of the south at
around 5 to 10 knots. The main exception to this is Icy Strait and
Lynn Canal, where speeds will be upwards of 15 to 20 knots tonight
and tomorrow, with speeds decreasing tomorrow night.

Late Friday into the weekend, wind speeds will increase in response
to the next approaching area of low pressure. While confidence in
speeds greater than 20 kts is high, confidence is speeds greater
than 35 knots is low. So for now, capped wind speeds at 25 to 30
knots. But as confidence in the track and strength of the low
increases, gales may need to be introduced. Stay tuned.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

SHORT TERM...NC
LONG TERM....NC
AVIATION...EAL
MARINE...GJS

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