Small Craft Advisory 950, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
1039 PM AKST Mon Nov 28 2022

.ANALYSIS AND UPPER LEVELS...

The low that brought the snow to Kodiak and the Bristol Bay region
is just southeast of Kodiak Island this afternoon and continuing
to track southeast. A high amplitude ridge continues to build
over Southwest Alaska which will bring in increased northerly
flow to southern Alaska and is clearing out the remaining clouds
from the region. This is also leaving a tight pressure gradient
along the north Gulf coast resulting in gusty winds through
channeled terrain.

Warm conditions persist over the central and western Bering Sea
under the upper level ridge. Over Southwest mainland Alaska the
temperatures are cold at the surface this afternoon, but this warm
ridge over the Bering is setting up that region for a strong
inversion to develop again over that area.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement again today. The more
southerly track of the storm over Kodiak which was discussed
yesterday was the correct track. Not too much else to say for the
near-term with the models as high-resolution ones are being used
to ascertain the timing and strength of the winds in Valdez and
possibly the Matanuska Valley.

Late in the week there will be a strong low in the
western/central Bering Sea. The overall agreement is much better
today and the GFS and GEM are very close to each other. The EC is
a bit farther east and weaker, but suspect it will shift closer to
GFS/GEM solution in upcoming model runs.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Snow across Kodiak Island tapers off this afternoon as a low
tracks southeast away from the island. Along the gaps and passes
of the Southcentral coast, gusty offshore winds persist as high
pressure and cold air blanket the interior. An upper-level
shortwave is expected to drop over the Eastern Chugach tonight,
strengthening the northerly winds through Thompson Pass and Valdez
in particular. Winds 40 to 50 mph with gusts up to 80 mph are
possible, thus, a High Wind Warning is in effect for these two
areas from this evening through Tuesday evening. A Matanuska
Valley wind is also expected to develop from this evening through
tomorrow evening. As a ridge builds overhead Southcentral from the
west, strong offshore flow along the coast begin to relax on
Wednesday while cold and clear conditions persist.

An upper-level trough near eastern Russia will track southeast
across Southcentral on Wednesday afternoon through Thursday
morning. The minimal amount of moisture with this feature will be
blocked by the Alaska Range, so precipitation across Southcentral
should also be minimal. If anything, traces of snow may be
possible late Wednesday. A surface low develops over the Gulf late
Wednesday into Thursday while high pressure builds over the
interior. As a result, a tight pressure gradient will form along
the Chugach Mountains and gusty winds will likely develop again
along the Southcentral coast. The low will depart into the far
southeastern Gulf by Thursday afternoon and yet another upper-
level ridge will build across Southcentral from the west. Thus,
expect clear and cold conditions across the region on Thursday.

&&

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

The longwave pattern features a ridge over the Central Bering and
a trough over the Western Bering and NW Pacific. There is a jet
core of 100 knots near Pilot Point. On satellite imagery (GOES
Airmass RGB) there is a mature low south of Kodiak with the
occlusion bent back towards the AKPEN which is still producing a
light band of snow and is present on King Salmon's radar. Earlier
today blowing snow was observed over portions of Southwest AK and
9 inches of snow fell in Naknek. Tuesday is going to be dry. A
upper level disturbance will drop down from NE Russia and bring
another round of wintry weather to Southwest. Nunivak will get
precipitation first and then Bethel will take a direct hit
Wednesday. This is a fast moving storm. Significant accumulations
are not expected at this time. The main concern with this system
is p-type (freezing rain vs snow vs sleet vs rain or some combo).
Stay tuned for more details.

&&

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

The longwave pattern features a ridge over the Central Bering and
a trough over the Western Bering and NW Pacific. There is a jet
core of 100 knots near Attu. On satellite imagery (GOES Airmass
RGB) there is a mature low south of Kodiak with the occlusion
bent back towards the AKPEN which is still producing a light band
of snow. Additionally, there is another mature low near Kamchatka
that has brought a cold front to the Western Aleutians. Also on
satellite imagery (CIMSS Mimic PW) there are 2 discernible fetches
of moisture from the Central Pacific that are entrained into each
low. The models bring this moisture to the Aleutian chain and into
the Bering this forecast period. Expect gales and small crafts.

&&

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

Overall model agreement with deterministic and ensemble guidance
is fairly good in the long term with above average predictability
through Sunday before model solutions diverge. The notable weather
features include a high amplitude ridge over western Alaska and a
series of upper shortwaves and attendant surfaces lows attempting
to break down the ridge or ride over it's axis from a deep trough
over eastern Russia. The first shortwave and surface low will
transit the Bering Strait on Friday, with it's front likely
bringing an initial bout of rain followed quickly by snow to the
Kuskokwim Delta and River areas as the system occludes and much
colder air returns aloft. Other than some light precipitation and
gusty onshore winds, this system won't have much impact on the
AOR.

The primary focus for the long term will be a strong storm
developing along the southern periphery of the Russian trough and
moving quickly into the Western and Central Bering Saturday. This
looks like a likely high wind scenario for the Central and
Western Aleutians with widespread high seas and gale to storm
force winds across the Bering Saturday and Sunday. Models have
trended more towards yesterdays ECMWF track into the Gulf of
Anadyr, which would put the western coast of Alaska into
south-southeast flow. Lunar cycles are not supportive of a high
high-tide so that should help mitigate any coastal flood issues in
addition to the fetch of wind and waves no longer being as
favorable (south-southeast instead of southwest) for high water.
There remains a possibility for sea ice related issues but this
remains uncertain at this time.

As this strong low moves north into the High Arctic another will
be quick to follow. The main impact from this system will be a
sweeping front that will move across the Bering Sea Monday,
reaching the coast Monday morning. With the occlusion of the
previous low and additional cold air from this system, the
atmosphere will cool considerably, bringing the return of normal
winter weather to the region. The two subsequent storms will
likely be enough to break down the ridge or at least shift it far
enough to the east, to return precipitation to Southcentral.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 131.
MARINE...Gale Warning 127
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
LONG TERM...CJ