Small Craft Advisory 932, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKST Thu Dec 3 2020

.ANALYSIS AND UPPER LEVELS...

A broad upper trough extends southeastward over the mainland. Weak
waves rippling trough the southwesterly flow aloft are maintaining
some light snow/flurries across parts of Southcentral and
rain/snow showers over the Gulf. Out west, a weak low near
Nunivak Island is producing a little light snow as it tracks
eastward across the Kuskokwim/Yukon Deltas. Patchy fog was noted
along the Bristol Bay Coast into the afternoon hours. A series of
at least 3 significant surface lows were evident along a broad
baroclinic zone extending from just south of the Central Aleutians
to southeastward across the Northeast Pacific. The further west
of the surface lows produced storm force easterly winds over the
coastal marine waters south of the Central Aleutians and general
gale conditions across the remainder of the Aleutians and Southern
Bering Sea.

&&

.MODEL DISCUSSION...
The general synoptic fields are in fair agreement through the
short term forecast period (into Sunday). The main players
initially will string of lows south of the Aleutians. Then
attention shifts to a fairly broad storm system and front heading
north this weekend.

&&

.AVIATION...
PANC...VFR conditions will persist through this evening. There is
a possibility of IFR conditions and stratus and fog during the
overnight hours tonight and Friday morning. Light winds will
persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Sunday afternoon)...
Flurries will end this evening as low-level flow begins to
transition to more northerly. Some low stratus will likely linger
around the northern Cook Inlet region. The extent of leftover
cloud cover will determine how low temperatures fall across the
area. Quite a cold air mass is in place, which will allow
temperatures to fall in to the single digits in many places. How
low they actually go will depend on any lingering cloud cover and
winds. Friday and Saturday will be categorized by light northerly
winds in most places. The exception will be along the coast where
wind comes out of the mountain gaps. However, they won't be very
strong due to being mostly a drainage wind. The next front begins to
affect the northern Gulf of Alaska on Sunday, beginning as snow
for most coastal locations, changing to rain later in the day.

&&

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

A cold core high is expected to persist over the northern Bering
through the forecast period. This will bring clear, cold and dry
weather to Southwest through Sunday. Winds are expected to
increase out of the northeast on Saturday as a strong north
Pacific low approaches the AKPEN and strengthens the pressure
gradient. This may help to increase temperatures a bit by Sunday
as winds mix down the low level inversion. However, wind chill may
drop the apparent temperature as low as -25F over the interior
areas. The AKPEN itself will be impacted by the low Saturday
afternoon with the precipitation mainly over the high terrain and
coastal areas southwest of Port Heiden. To the northeast
precipitation is expected to be mostly downsloped, which will warm
areas to the northwest of the Aleutian Range.

&&

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

Two low pressure systems to the south of the Aleutian Chain are
expected to absorb into one by Friday afternoon. Meanwhile a very
strong north Pacific low will be moving to the east at
approximately 45N. Over the northern Bering mostly calm conditions
are expected underneath a region of high pressure. Weather will
begin to become active once again on Saturday as the strong north
Pacific low begins to turn north. Storm force winds and high seas
are expected over and to the east of the central Aleutians. By
Sunday model guidance begins to differ with the track of the low;
however, gale force easterly winds are expected over the eastern
Bering with northerly gap winds across the central and eastern
Aleutians and the AKPEN.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska: Off-shore winds through gaps and passes will be
present in the Western Gulf on Friday and cold air filters into
the Gulf. Outside of these gap winds, the Gulf stays quiet. There
is a weak low moving north into our forecast area Saturday, but
there is low confidence in this as long range models have been
very inconsistent. We are more confident in northeast flow that
develops over the Gulf on Saturday, which will enhance winds in
the Lower Cook Inlet and Shelikof Strait to small craft advisory.
However, there are still no major weather systems forecasted and
no winds above small craft advisory.

Bering: A low pressure system that has been becoming more
pronounced in models the past couple of days will be present just
south of the Central Aleutians Friday. It is expected to produce
weak gale force winds in the Central Bering Friday. We have at
least moderate confidence in this since its been in models for a
couple days now. This low should weaken and stay south of the
Aleutians over the weekend. Winds then shift to the northeast for
the Bering and could become as strong as weak gale force winds in
the Eastern Bering, but this part of the forecast is still being
honed. Otherwise the Bering remains quiet.

&&

.LONG TERM FORECAST (Days 3 through 7)...

A gigantic North Pacific low will basically influence much if not
all of the long term forecast. A couple shortwaves from this
system will spread to the eastern Aleutians and AKPEN as early as
Sunday morning, while the other couple of shortwaves races
northward to Kenai Peninsula and Prince William Sound (PWS) around
Sunday afternoon. A broad area of warm air advection from the
Gulf and North Pacific ocean will roll across Southcentral and
Southwest Alaska in the coming days, and this could lead to a
rainy pattern and/or mix with snow inland. Although much colder
temperatures at 850 mb may push as far north of Kuskokwim
Mountains and well west of Kuskokwim Delta earlier in the week,
the potential for snowy conditions is feasible as we take winds
and freezing level into account in the coming days...in as such
where snow may be limited mainly around the Gulf.

Models struggled a bit with the placement of the synoptic low
after Sunday night, but the mix rain/snow pattern looks quite
favorable on this latest model package. An upper level ridge over
the Bering will stall there for a couple days before moving
eastward, and depending on the strength of the aforementioned low,
the ridge will take its time trekking eastward through the middle
of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms: 174, 176.
         Gales: 130, 155, 165, 170, 172, 173, 175, 176, 179, 413.
         Heavy Freezing Spray: 160, 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...CB