Small Craft Advisory 332, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 AM AKDT Mon Apr 23 2018

.ANALYSIS AND UPPER LEVELS...
A large, elongated upper level trough/complex low stretches from
the Kamchatka Peninsula, across the entire Bering and into the
southwestern Gulf early this morning with three main circulations
impacting the area. The first is a strong, though now becoming
vertically stacked low tracking through the western Aleutians. As
the western Aleutians low tracks east, a low in the eastern
Bering is curving back towards the west and tracking into the
central Bering in response. The third low center in the
southwestern Gulf is currently weakening towards a trough as it
lifts north. An associated frontal system stretches across the
northern Gulf coast and is pinned in place between the low/trough
to the south and the upper level ridge extending from the Yukon
Territory over the Alaska Range and into interior Alaska.

&&

.MODEL DISCUSSION...
Models remain in good agreement through midweek with all resolving
the the triple point low rotating up over the Kuskokwim Delta
early Tuesday and the strong southwesterly jet pushing from the
Alaska Peninsula into the western Gulf and then to point at
southcentral Alaska after it. This good model agreement increases
confidence in the unseasonably strong southeasterly wind event
potentially impacting the area Tuesday.

&&

.AVIATION...
PANC...VFR conditions will continue. Ceilings will likely lower
a bit during the day Monday as upper level flow shifts to south-
southwest, but low level southeasterly flow will keep them in
the VFR category. The Turnagain wind will bend into the airport
Monday afternoon and strengthen into the evening hours. In fact,
with pressure gradients rapidly tightening ahead of the next
system, the southeasterly winds may just continue to strengthen
all the way through Tuesday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An active week is in store for Southcentral Alaska with a number
of unusually strong systems for this time of year rumbling
through. The first one is bringing rain to the north Gulf coast
today with just scattered showers inland. The exception could be
the Copper River Basin where satellite shows a bit more lifting in
the eastern half of the Basin. Winds will increase again through
the typical gaps today and then crank up a few notches tonight
through Tuesday. A strong front will push into the western Gulf of
Alaska and up Cook Inlet tonight which is associated with a large
low in the eastern Bering Sea. A significant warm push aloft will
be ahead of this front with some colder air moving in behind it
Tuesday night. This front will bring strong southeast winds into
the Anchorage area and Matanuska Valley and strong south winds
along the Copper River. Winds will make it into the Anchorage bowl
as they bend northwestward out of Turnagain Arm. It has been a
while since winds this strong have made it into town. The strong
winds will mostly keep the area dry with the best shot of rain for
Anchorage and the Matanuska Valley late Tuesday afternoon through
mid evening as an upper level wave moves through. There is also
some questions as for snow amounts Tuesday afternoon into Tuesday
night for areas north of Talkeetna. Talkeetna will be on the
borderline for snow, but areas north of there should be able to
get mostly snow by Tuesday night with perhaps a number of inches
of accumulation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level low situated out over the Bering Sea will continue
to support an active weather pattern over the SW portion of the
state through mid-week, reminiscent of a pattern typically seen
during the fall. A series of short-wave troughs will continue to
sweep across SW Alaska today bringing rain and snow showers to the
region with persistent cloud cover. A pair of surface lows over
the Bering will rotate around each other then merge into a single
low center by Tuesday morning. At the same time, the upper level
low will reorient itself and dig south allowing a secondary
surface low to rapidly form near Bristol Bay and track north over
the SW mainland on Tuesday. This system will be aided by a strong
120 kt southwesterly jet which will help to pump in a large plume
of moisture to the mainland and bring strong southeasterly winds
to the surface on Tuesday. Winds will be strongest through
channeled terrain including through the Kamishak Gap and out
across Lake Iliamna, where winds could gusts as high as 50 mph at
times.

As the system pushes east Tuesday night, long fetch gale force
southwesterly winds will develop across the southern Bering and
into Bristol Bay. This will lead to rising seas and rough surf
along the coast. There is the possibility of minor flooding and
beach erosion along the coast from Kuskokwim Bay south to the
Northern Bristol Bay Coast as storm surge coupled with high tides
could bring water levels up to 1-3 ft above high astronomical tide
(grass line) on Tuesday evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A large upper level low will continue to dominate the weather this
week over the Bering bringing cloudy, wet, and windy weather to
the area, or just another typical day in the Bering and
Aleutians. A pair of surface lows will continue to rotate around
each other today bringing showery weather over most of the
region. A stronger surface low will develop today over the Western
Bering as the upper level trough digs further south and amplifies
as a strong jet pushes north over the eastern Bering. This will
lead to widespread gale force winds across the southern Bering and
most of the Aleutians beginning this evening through the middle
of the week. The long fetch winds will increase wave heights over
this area, with seas on the Pacific side of the Aleutians
increasing to more than 20 ft by Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long range forecast beginning Tuesday night will be in an
active pattern as a broad Bering low spins multiple shortwaves
around its perimeter which spans across the state and surrounding
waters. Onshore flow supplies abundant moisture for showers to
develop with the embedded shortwaves as they move around the low
center which brings higher precipitation chances for the southern
mainland through mid week.

Late Thursday, the Bering low is kicked eastward as the next low
races up from the North Pacific to the western Bering. Models are
in good agreement on the timing of this storm reaching the
central Aleutians early Friday morning; however, they diverge on
the timing and track of the system thereafter. The main challenge
for models is resolving a ridge that builds into the southern
gulf ahead of the next approaching low. The ECMWF had the best run
to run consistency and also had good continuity between its
operation and ensemble solutions for the extended range forecasts.
Overall, only minor updates were made for second half of the
forecast as there is low confidence concerning the track of the
Bering low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 119 120 125 130 131 132 139 150 155 170 172 173 174
175 176 177 178 185 .

&&

SYNOPSIS AND MODEL DISCUSSION...JR
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...KH

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
129 PM AKDT Mon Apr 23 2018

AKZ155-242100-
Kuskokwim Delta-
Including the cities of Bethel, Hooper Bay, and Nunivak Island
129 PM AKDT Mon Apr 23 2018

...HIGH WATER LEVELS EXPECTED ALONG THE KUSKOKWIM BAY COAST
TUESDAY AFTERNOON THROUGH EARLY WEDNESDAY MORNING...

Strong southerly winds will lead to high water levels along
Kuskokwim Bay Tuesday afternoon through early Wednesday morning as
a storm tracks up the west coast of Alaska. While flooding is not
expected, high surf with water levels at or slightly above
highest astronomical tide levels is likely around the time of high
tide Tuesday afternoon and early Wednesday morning. Anyone with
equipment along the immediate coastline should take precaution to
protect it.