Small Craft Advisory 709, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKDT Thu Aug 17 2023

.ANALYSIS AND UPPER LEVELS...

Skies continue to clear over south central as an upper level
ridge builds over the area. Low ceilings and fog continue to burn
off over the Susitna Valley south of Talkeetna as well as the
Copper River Basin with partly cloudy and light winds noted. Low
clouds are slower to burn off north of Talkeetna where skies
remain mostly cloudy. Gusty gap winds in areas such as Whittier,
Seward, and Kodiak City will continue to decease this afternoon
and evening. Low ceilings, gusty winds and scattered rain showers
are noted to the west of the Alaska Range and over southwest
Alaska and extending south and west over Bristol Bay and the
Alaska Peninsula. Further west, satellite imagery depicts a band
of higher clouds moving through the Aleutian Islands as another
low approaches from the North Pacific Ocean.

&&

.MODEL DISCUSSION...

Models are in fairly good agreement with the weekend system moving
into the Gulf of Alaska. NAM is the farthest solution northward
and that would allow for more precipitation and wind for Kodiak
and along the coast. Overall trend in the track is more away from
the coast. Agreement decreases going into next week, mainly with
the strength of a trough dipping south from the arctic and the
following low pressure system Tuesday through Wednesday over the
Aleutians and Bering Sea, whose implications could impact not only
the Aleutians and Alaska Peninsula, but also Southwest Alaska.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Slight chance
for fog, but anything that develops is expected to be patchy.

&&

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

A relatively quiet pattern should continue to unfold through the
upcoming weekend, particularly in the near term as an upper ridge
over Southwest moves overhead by Friday. Offshore flow helping
much of the region stay clear and dry today should weaken as the
pressure gradient along the coast diminishes by Friday morning,
but cloud cover should stay fairly minimal through at least Friday
afternoon. There remains some potential for low stratus to move up
the Cook Inlet somewhere between Friday afternoon and Friday night
with up-inlet flow, but this appears a bit less likely given that
marine stratus has entirely cleared out over the Gulf this
afternoon.

From Friday night into Saturday, a weak low will move into the
Gulf near Kodiak Island and move well south of Middleton Island as
it progresses mainly east. Model agreement for this feature has
improved significantly compared to yesterday. It's likely what
limited rainfall we will see with this system will remain focused
along the coast near Prince William Sound and Kodiak Island, with
most of the interior mainly seeing an increase in cloud cover on
Saturday. Weak upper ridging will try to reestablish itself on
Sunday as the low moves into the southeast corner of the Gulf,
however it will most likely not be nearly as clear and sunny as
what we've seen today with west to southwest flow developing south
of a trough and low pressure system moving from the Bering Strait
into the Interior. Some of the rainfall associated with the trough
moving off to the north may sneak into northern parts of the
outlook area, mainly near the Talkeetnas and far northern Susitna
Valley on Sunday.

&&

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

High pressure continues to build over the Bering and Aleutians and
into Southwest, resulting in widespread marine low stratus and
areas of fog. Steady west to southwesterly winds promote light
upslope showers along the western slopes of the Kuskokwim
Mountains and Western Alaska Range. Chances for showers decrease
on Saturday as winds diminish and high pressure continues.

An upper level low and its attendant surface low are located near
the eastern Aleutians this afternoon and will track east into the
western Gulf late Friday into Saturday. The precipitation with
this system is expected to stay confined to the eastern
Aleutians/Alaska Peninsula and surrounding coast marine zones.

Also on Saturday, an upper trough and compact surface low enter
the western Bering and Aleutians from the Kamchatka Peninsula.
This system will produce widespread steady rain and gale force
winds as it tracks east. As the upper trough breaks off a
separate low that tracks into the North Pacific, the front looks
to weaken quicker than previously advertised with sustained winds
dropping below gale force late Saturday night over the western
Bering/Aleutians. Rain with the front dives south into the North
Pacific on Sunday morning, following the track of the upper low.
The main aforementioned trough continues tracking east into
Southwest Alaska, and it is expected to bring steady rain to the
Kuskokwim Delta and Lower Kuskokwim Valley for Sunday and Monday.

Yet another upper low and attendant surface low are advertised to
track from the North Pacific to the eastern Aleutians on Sunday
and then into the western Gulf on Monday.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

Uncertainty remains through the first half of the forecast
period, but looks to tighten up towards the end. A well developed
upper level Arctic low stays to the Northwest to North of Alaska,
with a trough extending through the Bering into the Pacific all
the way to Thursday. The remnants of the tropical system Lan
approaches the Alaska Peninsula Coast and slips to the East of
Kodiak Island, dissipating Tuesday. This will bring rain,
occasionally heavy from Kodiak into Southcentral Alaska during the
first half of the forecast period. A moderately strong Sea of
Okhotsk low drives South of the Western Aleutians before the
Bering trough redirects it into Western Alaska by Thursday.
Periods of heavy rain and gusty winds are expected across the
Eastern half of the Aleutians and Bering Tuesday through Thursday.

&&

SYNOPSIS AND MODEL DISCUSSION...ccc/rux
SOUTHCENTRAL ALASKA...as
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...af
LONG TERM...mk