Small Craft Advisory 933, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKST Fri Dec 4 2020

.ANALYSIS AND UPPER LEVELS...

A longwave trough extends from southwest Alaska over to the AlCan
border. A ridge to the south of this feature remains over the
eastern Bering. A weakening area of low pressure has moved inland
over the Kuskokwim Delta, bringing light snow to the northern
Delta. Three surface lows in the North Pacific are increasing
winds and bringing rain for the Aleutians as their associated
fronts approach the area. Besides some precipitation over the
central Gulf, Southcentral looks to remain largely dry. One area
to note is the presence of low stratus visible on webcams from
Palmer to Eagle River towards the Hillside, which could remain
throughout the day. Northerly flow aloft will usher in cold air
so expect chilly temperatures to continue throughout the day.

&&

.MODEL DISCUSSION...

Models are in fair agreement as to the synoptic pattern for the
short term.

&&

.AVIATION...

PANC...There is a possibility of MVFR conditions due to low
stratus through this morning becoming VFR in the evening. Light
winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Low level clouds have developed along the Chugach Mountains in
northern Cook Inlet this morning. The northerly flow off the Inlet
in the area will likely keep them around for much of the day.

An upper level trough over the Copper River Basin this morning is
keeping some light snowfall over the Richardson Highway corridor.
This snow will not accumulate much and should end later today, but
clouds will be slow to dissipate in the lower elevations of the
Basin as an inversion will help trap the moisture under it. There
is a better chance for clearing on Saturday for the Copper River
Basin.

By Saturday night, the next system will move into the Gulf of
Alaska and Kodiak Island. This will do what most fronts do over
Kodiak this time of year: snow will fall at the beginning of the
event and then it will switch over to rain for the majority of the
precipitation.

&&

.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 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 the 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 weak gale force winds in the
eastern Bering, but this part of the forecast is still being
honed in on. 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 race
northward toward the 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
as the Kuskokwim Mountains and well west of the Kuskokwim Delta
earlier in the week, the potential for snowy conditions are
feasible as we take winds and freezing level into account in the
coming days. However, snow may be limited mainly around the Gulf.

Models struggled a bit with the placement of the synoptic low
after Sunday night, but the rain/snow mix 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...Heavy Freezing Spray Warning 139 140 160 180 181
		 Storm Warning 150 155 172 174
         Gale Warning 132 165 170 171 173 175 176 179 180 412 413 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CRK
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...CB