Small Craft Advisory 732, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 AM AKDT Sat Sep 17 2022

.ANALYSIS AND UPPER LEVELS...

The powerful hurricane force low that has dominated the sensible
weather for the last few days, especially for western and
southwestern Alaska, slowly fills/weakens and transitions to storm
force as it continues to move off to the north towards the Bering
Strait this morning. The satellite presentation is textbook of a
strong system; the Nighttime Micrphpysics Satellite Product as
well as water vapor imagery both show a well defined and "wrapped
up" low pressure system. Its front continues to lash the Norton
Sound area while the southern end continues to impact the
Kuskokwim Delta/Kuskokwim River and the Pribolof Islands regions.
Bethel radar shows areas of rain moving through the Kuskokwim
Delta and Kuskokwim River Valley areas. The bigger stories with
this system continue to be gusty winds as well as coastal
flooding for Kuskokwim Bay and lower Kuskokwim River. A Coastal
Flood Warning remains in effect until 4PM this afternoon and a
High Wind Warning remains in effect until 10AM this morning.
Current observations reveal Bethel gusting to about 50mph.

Looking at the current configuration of the jet stream, it dives
southeastward out of eastern Russia/Kamchatka to the subtropical
North Pacific. Then it extends northeastward from the subtropical
North Pacific to Southcentral Alaska and curves southeastward
through the eastern Gulf of Alaska to the North Pacific. The deep
moisture fetch is once again noted in the CIMSS NIMIC Total
Precipitable Water Satellite product shows total precipitable
water values of at least 1.5" extending from the subtropical
North Pacific into the western Gulf of Alaska. This moisture is
being pulled northeastward due to the influence from the strong
Bering low.

Meanwhile, conditions across southcentral Alaska remain mostly
quiet. Middleton Island radar is picking up on rain showers
moving up Cook Inlet as well as the Kenai Peninsual, and a few
spotty showers around Prince William Sound. A weak surface low
resides in the eastern Gulf and continues to move southeastward
while a coastal surface ridge exists over the northern Gulf Coast.
The tight pressure graident between this ridge and the strong
Bering low, coupled with up- inlet flow, is helping to produce
gusty Turnagain Arm winds.

&&

.MODEL DISCUSSION...

Models continue to perform well with the major Bering low. All
guidance has the system continuing on its current northward
trajectory through the Bering Strait and into the Southern Chukchi
Sea through tomorrow afternoon. Guidance also is strongly
suggesting the development of an atmospheric river that first
begins to impact the Alaska Peninsula/far eastern Aleutians
Sunday morning before impacting the rest of southern Alaska on
Sunday night. Forecast confidence is becoming higher with the
development of the atmospheric river itself, but details on timing
and exact rainfall amounts still need to be ironed out. Confidence
is also above average on most of Southcentral getting
precipitation from this system too. However, odds are once again
tilting towards the Prince William Sound communities getting heavy
rain from this system Monday through the day Tuesday as it moves
eastward from the Alaska Peninsula.

&&

.AVIATION...

PANC...A front and associated upper waves of energy will cross
the area early this morning which will bring the chance of
precipitaiton through about 18z mid-morning today. Behind the
front, flow veers from the south to the southwest. This wind
direction change, coupled with up-inlet flow, will be conducive to
MVFR ceilings through the morning hours. Drier air works in
through the end of the morning to afternoon hours and ceilings
should predominantly return to VFR then. Winds look to remain
gusty mostly out of the south and southwest during the TAF period
due to synoptic pressure gradients and up-inlet flow.

&&

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

An occluded front and associated upper-level wave will continue to
move east across Southcentral this morning. A surface low is also
expected to spin up east of Kodiak Island, at the triple point of
the occlusion. As the front and upper-level wave move east, a
lee-side low will develop over the Susitna Valley. The result
will be an increase in the up-inlet flow and a transition from a
Turnagain Arm wind over Anchorage early this morning to a strong
up-inlet flow that will bring gusty southwesterly winds for Kenai
north to Palmer and Talkeetna. Showers developing over the Western
Kenai Peninsula this morning will also move east to Prince William
Sound. Scattered showers are also likely across the Anchorage
Bowl and Mat-Su Valleys this morning, but most of the
precipitation will remain east of these locations, and any showers
that do develop should quickly come to an end as the front moves
east over the Copper River Basin.

As the upper-level trough exits the region, a ridge will begin to
build over the region. Clearer and drier conditions will prevail
Saturday night through Sunday afternoon. Winds will also diminish
by late Saturday night or early Sunday morning. With the ridge in
place, low temperatures Sunday morning could drop to around
freezing for many sheltered locations. The challenge will be just
how quickly the winds diminish overnight Saturday. The other
challenge in the short term will be the extent of stratus over the
northern Gulf underneath the ridge and whether the weak southerly
flow due draws any of this marine stratus along the coast and up
Cook Inlet. Hi-res models are indicating a potential for this and
the forecast does reflect that, with clouds back in the forecast
for places like Cordova, Seward, and Kenai by early Sunday
morning.

By late Sunday, the next system moves from the North Pacific
toward the Alaska Peninsula. Light rain looks to overspread the
region from southwest to northeast late Sunday night into early
Monday morning. Gap winds will also increase Monday morning as a
front associated with an area of low pressure over Bristol Bay
moves from the western Gulf to the northern Gulf. This system
looks to be the next widespread rain maker across Southcentral
with steady rainfall likely for the Susitna Valley and a
potential atmospheric river event, with bouts of heavy rain, for
Prince William Sound and points east.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Tuesday)...

The strong low is now well into the occlusion process over the
Bering Strait but remains a very potent system at approximately
950 mb. Strong southwesterly winds and rain continue to sweep
across the Kuskokwim Delta this morning. It won't be until the
overnight hours when gusts start to fall below the 30 mph mark,
but the strong gusts to 60+ mph should move out of the region by
10 am. Storm surge and coastal flooding are expected to reach peak
intensity in the early morning hours and should slowly diminish
through through the morning as the tide goes out and winds
subside. There may be a slower response to flooding along the
Kuskokwim River and as such the Flood Warning for Napakiak and
Flood Advisory within the Delta will remain in effect until 8:30am
Sunday. Gusty winds will be slow to diminish today now that the
progression of the low has slowed down in it's northerly
trajectory. Rain will also slowly subside over the area through
the evening.

On Sunday, much calmer weather will return to the northern areas
of Southwest with some pockets of sunshine emerging throughout the
day. However, the system that impacted the region built a stout
ridge over the north Pacific. This will allow a weak shortwave
currently emerging from Kamchatka to round the southern periphery
of the trough and re-curve north into Southwest Alaska. This will
bring some stout rainfall to Bristol Bay and the Lower Kuskokwim
Valley on Monday until the system moves east into Southcentral on
Tuesday. Behind this system, westerly flow and showers are
expected.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Today through Tuesday)...

Elevated winds over the Central Bering today will slowly subside
as the strong low currently in the Bering Strait moves north and
weakens. Calm weather is then expected through the forecast period
with no major features moving through the area. Light westerly
winds and shower activity will persist. On Tuesday, a front
extending east from a Kamchatka low will move through the Western
and Central Bering.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Aleutians / Bering: An elongated area of low pressure across the
Bering moves into Western Alaska by Wednesday. Forecast confidence
is fair with the timing of movement. A front moves from the
Central Bering into the Gulf of Alaska by Wednesday. Generally
light winds over the Bering give way to a new system with gusty
southerly winds increasing to gales over the western Bering
Tuesday, and the Central Bering for Wednesday. Seas building to
20 feet over the Western Bering Wednesday.

Gulf of Alaska: A front enters the Gulf late Monday, and extends
across the Northern Gulf by Wednesday. Gusty Southerly winds ahead
of the front diminish late Monday, then increase as a new North
Pacific low brings widespread gales over the Central Gulf Tuesday.
These gales become a boundary jet along the North Gulf Coast for
Wednesday. Seas to 12 feet over the Northern Gulf and to 16 feet
to the East of Kodiak Island for Wednesday.

&&

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

Unsettled conditions are expected to continue through the
extended period with two more systems impacting Southern Alaska.
The beginning of the long term period begins with a strong upper
level ridge remaining in place across Western North America while
a deep trough remains entrenched over western Alaska. To the west
of this trough, another upper level ridge is present over the
western Bering/Western Aleutians. In between the upper level ridge
and ahead of the upper level trough will be deep, moist, and
southerly flow (AR- Atmospheric River) aimed right into
Southcentral. Multiple upper level shortwaves will move northward
towards Southcentral ahead of this upper level trough. While the
overall pattern is fairly high confidence, the details remain low
to moderate confidence. The reason being the EC and Canadian-NH
remain more progressive with the upper level pattern for Tuesday
and keep the trough more positively tilted to neutral before going
negatively tilted heading into Wednesday. The GFS on the other
hand, makes the upper trough go more negatively tilted earlier on
Tuesday afternoon as well as bringing up much stronger upper level
energy. Though, at this time, this solution appears to be the
outlier. With that said, either way, expect another prolonged
heavy rainfall event across Southcentral with the details
remaining highly uncertain at this time, especially in regards to
amounts. Recommend checking back for updates over the weekend as
the situation continues to evolve and models converge on the
correct solution.

For the remainder of the period, the upper level ridge over the
western Bering/Western Aleutians is expected to be broken down as
another potent storm system moves into the Bering Sea and Southern
Alaska with details (strength, intensity, and track) uncertain at
this point in time. This is important as it would affect where
the main impacts would be felt. Overall, this system will
basically reinforce the whole longwave trough keeping the region
in this very active and wet pattern through the end of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 155.
         Coastal Flood Warning: 155.
         Flood Warning: 155.
         Flood Advisory: 155.

MARINE...Storm Warning: 181.
         Gale Warning: 414, 412, 185, 180.

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DAN
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...MK/MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
238 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1000 AM     FLOOD            NAPAKIAK                60.69N 161.98W
09/17/2022                   BETHEL             AK   PUBLIC

            PUBLIC REPORTED ALL LOW LYING AREAS IN
            NAPAKIAK AND OSCARVILLE ARE FLOODED.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
241 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1200 PM     FLOOD            NAPASKIAK               60.71N 161.76W
09/17/2022                   BETHEL             AK   PUBLIC

            AIRPORT ROAD STILL HAS WATER OVER IT, AT THE
            LOW END. WATER DROPPING SLOWLY. STILL WINDY.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
249 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1030 AM     FLOOD            2 N BETHEL              60.80N 161.76W
09/17/2022                   BETHEL             AK   LAW ENFORCEMENT

            CORRECTS PREVIOUS FLOOD REPORT FROM 2 N
            BETHEL. ALLIGATOR ACRES FLOODED. BETHEL
            SEARCH AND RESCUE REPORTED WHILE PATROLLING
            ACROSS (BROWN) SLOUGH AND BOAT HARBOR WHERE
            WATER IS FLOWING 1 FT DEEP OVERBANK.
            ELSEWHERE ON THE EAST SIDE OF TOWN, THE MAIN
            ROAD IS SUBMERGED. RUNWAY WAS STILL DRY, BUT
            HOUSE AT THE END OF RUNWAY WAS BECOMING AN
            ISLAND. KUSKOKWIM RIVER OVERBANK AT SCHOOL
            AND WATER RUNNING BENEATH.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
251 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1030 AM     FLOOD            2 N BETHEL              60.80N 161.76W
09/17/2022                   BETHEL             AK   LAW ENFORCEMENT

            CORRECTS PREVIOUS FLOOD REPORT FROM BETHEL.
            ALLIGATOR ACRES FLOODED. BETHEL SEARCH AND
            RESCUE REPORTED WHILE PATROLLING ACROSS
            (BROWN) SLOUGH AND BOAT HARBOR WHERE WATER
            IS FLOWING 1 FT DEEP OVERBANK. ELSEWHERE ON
            THE EAST SIDE OF TOWN, THE MAIN ROAD IS
            SUBMERGED. RUNWAY WAS STILL DRY, BUT HOUSE
            AT THE END OF RUNWAY WAS BECOMING AN ISLAND.
            KUSKOKWIM RIVER OVERBANK AT SCHOOL AND WATER
            RUNNING BENEATH.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
255 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0130 PM     FLOOD            NAPAKIAK                60.70N 161.99W
09/17/2022                   BETHEL             AK   PUBLIC

            SOCIAL MEDIA REPORTED FLOODING IN FRONT OF
            THE SCHOOL.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
315 PM AKDT SAT SEP 17 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0215 PM     FLOOD            NEWTOK                  60.94N 164.63W
09/17/2022                   BETHEL             AK   PUBLIC

            REPORT CAME IN OF ENTIRE COMMUNITY IS
            INUNDATED WITH WATER. THEY ARE CUT OFF FROM
            THE AIRPORT. THEY ESTIMATED 100 FEET OF
            SHORELINE WAS LOST. 12 HOMES ARE FLOODED. A
            5,000 GALLON FUEL TANK WASHED AWAY. ABOUT 35
            PEOPLE DO NOT HAVE A HOME TO GO BACK TO.

&&

MV