Small Craft Advisory 940, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKST Sun Dec 6 2020

.ANALYSIS AND UPPER LEVELS...

An upper level low is currently stationed just south of the
eastern Aleutians, with its broad front extending across most of
the Bering and the Gulf. Gale force winds and high seas are being
observed from Saint Paul south across the central and eastern
Aleutians. Snowfall continues to dominate the precipitation type
for the eastern Aleutians, as temperatures hover right around
freezing. Winds have reached Gale criteria just south of Kodiak
Island as the front continues to move across the Gulf. On radar,
it has begun to snow in Kodiak, with a wave of precipitation
making its way over the Kenai Peninsula and towards Prince
William Sound.

&&

.MODEL DISCUSSION...

Models are in good agreement this morning. A NAM solution was
favored for the east with a NAM/GFS blend favored out west.

&&

.AVIATION...

PANC...Winds look to remain light and out of the north throughout
the day. Ceilings and visibilities could come down to MVFR, this
evening, as shortwaves around the approaching low in the Gulf move
over the terminal.

&&

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

A strong low south of Kodiak Island has a front that is pushing
onshore along the north Gulf coast today. This low is moving
rather slowly, especially compared with the front, which will
keep northeasterly surface flow and then southeasterly flow
aloft. This pattern also means that there will not be the gusty
southeast winds making it into Anchorage or the Matanuska Valley
as has been the case in recent systems. In addition, there is
quite a bit of warm air aloft with this system and that is a set
up for potential freezing rain in the Cook Inlet region for Monday
into Monday night in particular.

The arctic front will get pushed all the way west to the Alaska
Range and this will most likely downslope out the vast majority of
the precipitation in the areas most likely to have a temperature
profile conducive for freezing rain. These areas are from Kenai
to Anchorage to the Matanuska Valley. All that to say is that
there is a chance for freezing rain from Kenai to Wasilla, but it
likely will just not be precipitation. By Tuesday morning the
colder air should move back up Cook Inlet again and turn precipitation
to all snow.

&&

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

An active weather pattern is expected for the start of the week
across Southwest. A strong low centered south of the Alaska
Peninsula will lift into the northern Gulf of Alaska through
tonight. Meanwhile, an upper level trough over northwest Alaska
will drop southward, becoming centered over the eastern Bering
Monday morning. Plenty of cold air is expected to accompany this
feature, and snow will develop across much of Southwest on Monday.
In addition to snow, gusty northerly winds are expected,
especially across the Kuskokwim Delta. A Winter Weather Advisory
has been issued from midday Monday through Tuesday morning for the
Kuskokwim Delta, as gusty winds and snow will create blowing snow
conditions, reducing visibility to one half mile or less at
times.

As precipitation tapers from west to east on Tuesday, and the low
tracks eastward through Wednesday morning, cold northerly flow
will fill in over Southwest with continued gusty winds along the
coast. Quieter conditions are expected for Wednesday as a ridge of
high pressure builds in from the west.

&&

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

A storm force low centered south of the Alaska Peninsula will
track northeastward into the Gulf tonight. As this low departs,
another low forms over the eastern Bering in the vicinity of
Bristol Bay Monday afternoon. This will keep gusty northerly flow
in place over the central and eastern Bering. The eastern
Aleutians and southern Alaska Peninsula may see accumulating
snowfall Monday into Tuesday. Snow combined with gusty
northwesterly winds may create blowing snow conditions and make
for reduced visibility at times. By Tuesday night, attention
shifts westward as a complex low approaches the western Aleutians.
While there is still plenty of disagreement across model
solutions, the general signal is that a strong surface low will
form south of Amchitka Wednesday morning.

&&

.MARINE (Days 3 through 5)...

Bering: Tuesday starts with strong north-northeasterly flow in the
eastern Bering and quiet elsewhere. Tuesday night into Wednesday,
models are showing a strong low pressure system moving into the
western and central Aleutians. Models have a good amount of
disagreement on this low, but there is enough information to know
that this system will have a front with at least gale force winds
with it. These winds will impact the western and central
Aleutians/Bering. This low should also induce easterly flow for
the eastern Bering for most of the week.

Gulf of Alaska: On Tuesday a strong low will just be exiting the
Gulf of Alaska and weather should be calming down. Southwest winds
should be in place behind it. Another low is anticipated to enter
the Gulf of Alaska on Wednesday, but will be much weaker with
little to no marine impacts. Models remain in disagreement on the
track of this next low but all agree it won't be as strong.
Therefore, we have moderate confidence in the forecast of low
pressure with little weather from it next week.

&&

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

Significant uncertainty persists in the long term guidance. This
poor performance leads to little confidence in what will happen
mid to late next week. Right now, we know there will be a strong
low just south of the western and central Aleutians Wednesday and
low pressure in the Gulf of Alaska. However, placement of these
system varies substantially between models. To further compound
the issue, moving forward in time from mid week to the weekend,
models progress these systems in very different directions.
Therefore, it's not possible to tell what will transpire, which
results in low confidence overall for the long term picture. So,
we know we will have generally unsettled weather for maritime and
coastal environments, while interior areas look to be quiet.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Freezing Spray Warning: 139 140 160 180 181 414
		 Storm Warning: 155
		 Gale Warning: 119 120 130 131 132 136 139 150 160
		               165 170 172 173 174 179 180 181 185
					   352
FIRE WEATHER...NONE.

&&

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