Small Craft Advisory 882, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKST Sun Nov 6 2022

.ANALYSIS AND UPPER LEVELS...

At upper levels, a ridge of high pressure stretches from the
central Bering east into the central Mainland, with its negatively
tilted axis located over the eastern Bering. At 850 mb, southerly
flow along the backside of the ridge advects warmer air over much
of the Bering and Aleutians, while northerly flow downstream of
the ridge keeps colder Arctic air over Southwest and Southcentral
Alaska. An impressive atmospheric river is visible on satellite
over the northern part of the state.

As a result of the ridge, Southcentral and Southwest Alaska
continue to see clear skies and colder temperatures. Gusty
northerly winds across Southcentral continue to diminish this
morning, with the strongest winds still lingering near Valdez and
out of the Copper River Delta. Out west, a North Pacific low and
its front are lifting across the central and eastern Aleutians
into the southern Bering. The front is bringing heavy
precipitation, storm force winds, and warm air along with it. The
strongest winds this morning are located between Adak and
Unalaska. Over the western Bering and Aleutians, another front
lingers and maintains light rain over that area.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the next
few days. There is consensus for a surface low to develop near
Kodiak Island and the Kenai Peninsula on Wednesday morning.
However, model agreement with this feature begins to diverge
later in the week. The GFS tracks the low over the Gulf by
Thursday morning, while the EC moves the low snug along the Gulf
coast and into Prince William Sound around the same time. The
exact track the low ends up taking will have an impact on the
wind field and precipitation location, timing, and amounts for
Southcentral.

&&

.AVIATION...

PANC...VFR conditions will persist. Gusty northerly winds will
continue diminishing this morning and into the early afternoon,
after which time the winds will remain light. Expect clear skies
through the TAF period as a high amplitude ridge builds in from
the west.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 2: Today
through Monday night)...

The gap winds will decrease through the day as a ridge begins to
move towards Southcentral and the pressure gradient weakens.
Otherwise, expect mostly clear skies and below normal
temperatures through tonight. On Monday morning a frontal system
will move towards Kodiak Island and the western Gulf bringing
gale force easterly winds and rain and snow across Kodiak Island.
This front will move north towards the Kenai Peninsula and then
towards Anchorage by Monday afternoon and evening bringing
initially snow along coastal locations but transitioning to rain
or a mix of rain and snow. Elsewhere snow is expected with light
accumulations of snow expected around the western Kenai Peninsula,
Anchorage and the Matanuska valley through Monday night. The
Turnagain wind will also increase on Monday, but there is model
disagreement if it will bend into west Anchorage so low forecast
confidence for winds on Monday afternoon through the overnight
hours. The GFS has a surface low developing near the Kenai
Peninsula which would keep the winds northerly across west
Anchorage with down inlet flow, but other models do not form the
low. This will allow the low near western Alaska to create up
inlet flow and gusty southeasterly winds for west Anchorage.
Finally, this front will bring warmer temperatures across much of
the area ranging from the teens and 20s across the Copper River
Basin and 30s elsewhere.

&&

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

One last day of clear skies and sunshine for Southwest Alaska with
an upper level ridge exiting off to the east. Active weather
returns with the approach of a front extending off a North
Pacific low. Models have come into better agreement indicating a
more rapid approach of warmer air and a quicker transition to rain
than previously anticipated. This means, less snow overall is
expected for most of Southwest Alaska, with highest amounts being
north and west of King Salmon, including Dillingham, New Stuyahok,
and Koliganek, and west towards Twin Hills, Togiak, and Platinum,
with 4 to 8 inches of snow accumulation possible. Thus, Winter
Weather Advisory has been issued. With a surge of warmer air,
temperatures will approach freezing early Monday morning, allowing
for a heavy, wet snow. Gusty southeasterly winds impacting the
Bristol Bay coast during periods of heavy snow could incite some
visibility issued due to blowing snow. Temperatures will rise
above freezing later Monday morning, and snow will transition to
rain. Mid-morning, however, with temperatures hovering around
freezing, there is a chance for brief periods of freezing rain
from King Salmon to Dillingham. Gusty south-southeasterly winds
and areas of light precipitation will continue into Monday night,
diminishing by Tuesday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A North Pacific low lifts into the southern Bering Sea this
morning. The associated front is transporting with it storm force
winds, heavy precipitation, and warm air. Storm force winds are
expected to track along the Eastern Aleutians and southern Alaska
Peninsula today and tonight and push into Bristol Bay Monday
morning. Channeling is expected to increase winds through Dutch
Harbor and Cold Bay, and through the gaps and passes north of the
AKPen. The low continues north through Monday morning, exiting
into the Bering Strait. Winds will come down and precipitation
will diminish into Monday morning. A secondary weak surface low
moves over the Eastern Aleutians overnight Monday, bringing
another quick shot of rain to the Eastern Aleutians and southern
AKPen.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

The overall pattern progression for the long term starts off
fairly clear with reasonably close model agreement, but this
quickly deteriorates later in the period. On Wednesday, an upper
trough will be positioned over the eastern Gulf and Alaska
Peninsula (AKPen), with an associated surface low slowly moving
across the eastern Gulf. This system will be shouldered by upper
ridging both upstream over the Bering/Aleutians and downstream
over the Yukon and Southeast AK. There is already some notable
model spread for the location of the main system in play over the
Gulf by this point. The ECMWF brings the surface low as far north
as the Prince William Sound (PWS) on Wednesday morning, while the
Canadian shows a slower progression, with the low beginning to
stall out over Kodiak Island. The GFS projects a separate low
wrapping in from the southeast that phases with the main upper
level trough, resulting in a much stronger low persisting over the
Gulf compared to the consensus all the way into Thursday morning.
These differences open up a lot of forecast uncertainly already
from Wednesday to Thursday, particularly in terms of winds over
the Gulf and inland extent of precipitation over the southern
mainland. One factor that is more clear is that the frigid air
mass will be long gone by this point, with some coastal and lower
elevation spots around Southwest and Southcentral likely warming
back to or even above freezing by the middle of next week.

Looking out farther in time, the forecast details and even the
larger scale pattern resolution begins to fall apart, especially
by next weekend. Large differences begin to appear for a North
Pacific low expected to move approximately along the Aleutians
from Thursday to Friday, with some solutions lifting the low north
into the eastern Bering, while the GFS tries to plow the center
straight east and south of both the Aleutians/AKPen and Gulf by
Friday. Similarly significant differences are apparent for another
low tracking towards the western Bering out of the Kamchatka area
going into Friday and Saturday. It appears the models are
struggling quite a bit with an increasingly 'blocked' large scale
pattern developing late next week, where significant meridional
and even retrograding (easterly) upper level flow results in
slow, meandering progression of storm systems across Alaska.
Needless to say, there is much left to be determined for the
forecast from Friday onwards at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 161.
MARINE...Storm Warning: 155, 160, 165, 170, 172, 174, 180, 414.
		 Gale Warning: 130-132, 136, 137, 150, 171, 173, 175,
					   176, 179, 181, 185, 352, 412, 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...AS