Small Craft Advisory 828, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 PM AKDT Fri Oct 30 2020

.ANALYSIS AND UPPER LEVELS...

The pattern aloft features a shortwave trough sliding through the
Copper River Delta and towards Canada. A vertically stacked and
decaying low sits south of Atka, with a surface front protruding
to the north and east, laying just south of Kodiak.

A weak low over the north eastern Gulf continues to move into
Canada this afternoon. This low, combined with a shortwave to the
north, is bringing light snow showers to the eastern Copper River
Delta.

For Southcentral Alaska, northerly flow has begun to increase.
Despite the winds, clouds formed across much of the Anchorage
metro this morning and finally dissipated once the sun heated the
atmosphere up.

&&

.MODEL DISCUSSION...

Models are all in great agreement through the short and mid range
forecasts. The biggest disagreements start to show Monday/Tuesday
but are well outside of the forecast area. Given the consistency,
confidence remains high on the wind forecast extremes coming up
later this weekend.

&&

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

&&

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

A surprisingly active weather pattern is moving into the area,
despite a lack of precipitation nearly everywhere. Presently, the
focus is on Kodiak. A light northwesterly surface wind in town
resulted in all snow falling in the area. These snow showers will
continue through the day, but the combination of daytime heating
warming paved surfaces and temperatures at or slightly above
freezing along with light precipitation rates should confine any
very minor accumulations to grassy surfaces only. The fog that has
haunted the Cook Inlet region the past few days has finally
dissipated this afternoon. As the winds gradually increase over
the next several days, no more fog concerns are expected.

A strong upper level trough and associated push of Arctic air are
moving across all of Southcentral this afternoon. Counteracting
this cooling will be the gusty winds that will gradually increase
with time in most areas, particularly through the gaps. The
primary gap wind to take note of will be Thompson Pass. Once the
upper level wave finally passes south of the Pass Sunday and
Sunday night, the northeasterly flow behind it aligned with the
already gusty northeasterly winds and additional downward forcing
makes high winds through Thompson Pass a strong possibility
Sunday night into Monday. There remains some disagreement in the
models as to how strong the winds will be and when the atmospheric
winds become fully unidirectional, but headlines are probable
with future forecasts, barring there aren't any substantial shifts
in forecast thinking. Blowing snow will be present the next
several days as winds increase, but should not amount to
substantial decreases in visibility since no additional snowfall
is expected.

While the airmass will be by far the coldest of the season, the
strong winds accompanying the arrival of the air mass should
greatly temper how cold the temperatures get in wind-prone areas.
Seward, Whittier, Valdez, the Matanuska Valley including Palmer
and Wasilla, and north of Talkeetna through Broad Pass should all
see gusty winds increasing Sunday and through the day on Monday.
Anywhere the winds are calm, the temperatures will plummet.
However for most of the area, favorable upper level support should
support most areas having a decent wind through the night. The
breezy, but not particularly gusty areas will include west
Anchorage, Kenai, along the coast of the Kenai Peninsula and much
of the Copper River Basin. Thus, have nudged forecast lows
significantly warmer owing to those winds negating much of the
cooling from the cold air mass. If any of those windier spots see
calmer winds overnight for any substantial amount of time, the
overnight lows will be much colder than advertised.

&&

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

Overnight low temperatures across the lower Kuskokwim Valley and
Kuskokwim Delta will remain in the teens through the weekend,
while air temperatures in the lower 20 to upper 30 degrees
Fahrenheit will be felt across Bristol Bay and AKPEN in the
coming days. Mostly sunny days and clear to partly cloudy skies
will persist into early next week, thanks to an upper level ridge
nearby which will keep the region especially the coastal areas
relatively quiet.

A shortwave from a polar low will dive past Kuskokwim Mountains
early Saturday morning, and this could bring another brief round
of light snow across Kuskokwim Valleys and Kuskokwim Delta
Saturday morning.

&&

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

An extensive occluded front across the central and eastern
Aleutians will continue to bring steady light rain there, with
gales over much of the Aleutians east of Adak. Storm force winds
are expected to pass through Amukta Pass, which lies between
Nikolski and Atka Island by tonight. Hazardous wave heights and
strong gales will continue into Saturday morning, then gradually
diminish by Saturday afternoon. The next frontal system from
Northwest Pacific will re-invite gales over the western Aleutians
on Saturday night, and this may last for a day should the
circulation weakens and stay south of the Aleutians in the coming
days.

&&

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

A North Pacific low and front tracks southward through Wed.
Models are mixed, but confidence is good for easterly small craft
winds and waves with local gale force winds over the Aleutians and
Alaska Peninsula diminishing Tue. Upper level troughs bring
northerly small craft with local gale force winds over the Eastern
Bering and Bristol Bay Tue and Wed. A strong front approaches the
Western Aleutians and Bering with widespread high end gale force
winds for Wed.

For the Gulf, a weakening low over the Northern Gulf lingers
through Wed. Track and development vary between models, but two
areas of westerly gale force winds and waves occur Mon, the first
from the Barren Island into the Central Gulf, the second from the
Alaska Peninsula into the Western Gulf, diminishing Tue. These two
areas become northwesterly gale force winds that fan out into the
western Gulf for Wed.

&&

.LONG TERM FORECAST (Days 4 through 7)...

The main weather story moving through the weekend and into next
week will be the intrusion of arctic air across the Southern
Mainland in the wake of a vigorous surface low moving from the
western Gulf to the Alaska Panhandle. The core of the coldest air
looks to arrive on Monday as the polar upper-level low settles
over Southcentral. 850 mb temperatures (~4500ft AGL) look to
plummet to -18 to -20C across interior Southwest and over the
Anchorage Bowl and Kenai Peninsula. The Copper River Basin could
see 850 mb temperatures fall to -22 to -25C. This would translate
to highs struggling to climb into the teens to lower 20s for most
locations not immediately along the northern Gulf coast by early
next week. The initial thinking for the extended forecast was that
with the cold airmass, that daytime and overnight temperatures
would bottom out. Despite the cold, the strong winds will actually
help to keep temperatures up and we've made those changes in the
forecast.

Gusty outflow winds will also remain a potential along
the immediate coast through next week due to the build up of
colder air inland and a lingering gradient between an interior
ridge and trough along the coast. Models, however, are indicating
that one or more compact, meso-lows could spin up at the surface
over the northern Gulf due to the interaction of the upper-level
dynamics and the increased surface winds and thermal gradient. If
this does happen, there could be additional cloud cover that could
help moderate temperatures nearer the coast and also bring about
an increased chance for snow showers through early next week.

Farther to the west, a ridge of high pressure will build over the
western Aleutians and expand east by next week. Multiple
shortwaves diving south between the ridge and the aforementioned
polar low to the east will allow for clouds, snow showers, and
gusty northerly winds to persist from the central Bering to the
Southwest Alaska coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 155-173 175-180
		 STORM 174
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHCENTRAL ALASKA...JPW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...SS