Small Craft Advisory 536, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKDT Sun Jul 12 2020

.ANALYSIS AND UPPER LEVELS...

An upper level low over Southwest Alaska continues to generate
showers over the greater Bristol Bay area this morning. Another
swath of showers over southern Cook Inlet and Prince William Sound is
moving to the northeast. Farther west, a pair of surface lows are
slowly tracking eastward south of the Aleutian Chain. A layer of
marine stratus remains in place across much of the Bering as well
as the Gulf of Alaska this morning.

&&

.MODEL DISCUSSION...

Model solutions remain in fairly good agreement. There is good
consensus that the upper level low currently over Southwest
Alaska deepens and moves over the Gulf of Alaska. At the surface,
there is less consistency regarding where this low tracks beyond
Tuesday. The NAM was the preferred model for the placement of this
low in the Gulf. Farther west, model solutions agree on an
inbound low over the western Aleutians midweek, though there is
less consistency with the track and strength of this low as it
progresses eastward. In the meantime, higher resolution models
were preferred, particularly given the convective environment.

&&

.AVIATION...PANC...Gusty southeasterly winds may lull early this
morning before ramping back up by late morning. Low level wind
shear will be the main concern during the day Sunday before winds
diminish by Sunday evening. Ceilings should remain above VFR but
may drop to MVFR with passing showers.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today and
Monday)...

The upper level low over Southwest Alaska will move southward
through the day today. This will cause the broad flow over
Southcentral to turn southwesterly. The southwest onshore flow is
beginning to transport a much more stable marine air mass into
Southcentral, along with additional Pacific moisture. Thus, the
weather pattern today will feature scattered shower activity for
much of Southcentral from the southern Susitna Valley south and
east. North of there, the unstable air mass along with an airflow
that turns more out of the east later in the day will support a
chance of isolated thunderstorms along the Alaska Range and
Talkeetna Mountains. The overall coverage of thunderstorms will
be much less today than previous days.

Another changing aspect to the forecast will be the gusty gap
winds through Turnagain Arm, Knik River Valley, and the Copper
River Basin. As the low level flow turns southeasterly today, the
winds will be forced through those gaps. Meanwhile the low over
Southwest Alaska will help to further pull those winds westward.
Today should be a bit cooler than yesterday for most of
Southcentral, primarily due to significant cloud cover and
scattered rain shower activity.

Then on Monday, the upper low driving the weather across
Southcentral will shift eastward near Kodiak Island in the
morning. This will aid in the development of a North Pacific low
over the Gulf through the day. Strengthening easterly windflow
ahead of the low will get up to gale force across the offshore
waters south of Middleton Island. Meanwhile, the lift to the east
of the upper low which has been over Southcentral the past several
days will shift with the low over the Gulf. Thus, most inland
areas will finally get a break from all precipitation on Monday as
ridging and sunshine return, along with somewhat warmer
temperatures. Cloud cover and rain will persist along the coast
due to the Gulf low, but since the low is expected to track
eastward, the strongest winds will remain well offshore of the
coast. Even some coastal locations may see some sunshine at the
end of the day. The low will also begin turning the winds to the
offshore northerly direction on Monday, which in addition to
beginning a drier weather pattern, will end the gap winds as well.

&&

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

The upper level low that tracked south into the region yesterday
can be observed spinning in place over Southwest AK. This is as
expected. This means more thunderstorm activity today, though not
quite as intense as yesterday. Widely scattered thunderstorms are
in the forecast. This will be the last day of widespread
convection. Weather begins to clear out tomorrow with quiet
weather for the first part of this week.

&&

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

Little change to the weather again today. High pressure continues
to dominate much of the Bering with stratus and fog trapped
beneath it. Low pressure continues to march slowly east just south
of the Aleutians, with its stretched out front riding right over
the islands themselves. This will continue cloud cover and rain
showers for them. More of the same for the next few days with high
confidence in the forecast.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

High pressure lingers across the Bering with easterly winds and
waves across the lower half and southerly winds and waves over the
upper half through Thu. High uncertainty comes with the initial
position and track of a North Pacific low, bringing problems with
movements and wind directions with the low through Thu. Confidence
is good for less than small craft winds and waves south of the
Aleutians through Thu.

Over the Gulf, a low center will track across the Gulf, however
certainty is low for frontal positions through Thu. East to
southeast winds and waves expected across the northern Gulf less
than small craft speeds, shifting to northerly winds and waves
around Kodiak Island and the western Gulf by Thu.

&&

.LONG TERM FORECAST (Days 3 through 7: Monday through Thursday)...

By Tuesday, the upper level low that is near Southwest Alaska
today will have moved over Kodiak Island and be in the central
Gulf of Alaska. This will start the period with high pressure over
Southwest Alaska and a front along the north Gulf coast. The high
pressure is not terribly strong but should spread over
Southcentral Alaska for the middle of next week. Southwest Alaska
will be susceptible for low stratus to advect into the region off
the Bering Sea, though rainfall should mainly be afternoon and evening
showers over higher terrain.

Afternoon and evening showers are also likely over interior parts
of Southcentral Alaska throughout the period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...351.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...MK/EZ