Small Craft Advisory 8, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKST Tue Jan 4 2022

.ANALYSIS AND UPPER LEVELS...

Arctic high pressure centered over the Yukon continues to dominate
Alaska's weather this afternoon. The high is keeping strong
offshore flow ongoing through the gaps, especially those draining
the Copper River Basin. It is also responsible for the cold
conditions we are seeing across all of the mainland. Temperatures
are running 15 degrees or so below normal over much of the
mainland. The steady strong winds also are causing extremely cold
wind chills over portions of the area, especially through Thompson
Pass. The Wind Chill Advisory for Thompson Pass continues through
6pm Wednesday. The High Wind Warning also remains in effect for
the Matanuska Valley, though winds have subsided below hurricane
force, they are still strong enough, occasionally gusting above 50
mph, to resuspend debris from the bora wind storm the past couple
days. Wind chills remain below zero in the windier areas of
northern Palmer and Wasilla. On the positive side, however, the
Arctic high is also keeping all the clouds confined to the coast,
so nearly all of mainland southern Alaska is enjoying full
sunshine and clear skies.

Kodiak Island is getting hit with a series of weak waves, causing
periods of light snow over the island. Any significant reductions
in visibility due to heavier snow are brief due to the transient
nature of the snow showers.

In the upper levels, a rex block upper level pattern has set up
with a large area of strong high pressure over eastern Siberia,
with an upper level low near Adak, moving westward. A 115 kt
easterly jet has developed between these features from the central
interior of mainland Alaska over much of the Bering and looping
out ahead of the upper low over the Western Aleutians. Much of
southern mainland Alaska is between these features, resulting in
generally light upper level flow. The southern edge of the jet
streak is slowly sinking southward, and is currently located over
the northern Copper River Basin and northern Susitna Valley, then
paralleling the Kuskokwim River.

&&

.MODEL DISCUSSION...

The models are in great agreement through Thursday afternoon, with
the primary large-scale disagreement is on where the center of a
North Pacific low tracking south of Adak is by that point. The
front and area of stronger southeasterly winds across much of the
Bering, Eastern Aleutians, and AKPEN is in great agreement. A
large area of high pressure will be in place near or over Kodiak
Island Thursday. With the weather remaining cold and quiet over
the mainland, and any precipitation being confined to Kodiak
Island westward across the Aleutians, forecast confidence is very
high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. A stray
northerly gust or two this afternoon and tonight can't be ruled
out, but they should be few and far between.

&&

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

Relatively quiet but clear and cold conditions will persist as a
strong Arctic ridge drapes across Southcentral through Friday.
Daytime temperatures will gradually warm back up and could reach
up in the teens by Friday, with more sunshine and partly cloudy
skies across Southcentral through much of the short term. Winds
continue to taper off along Matanuska Valley this afternoon and
parts of Prince William Sound, and the High Wind Warning for
Matanuska Valley including wind data are currently being re-
assessed at the time of the AFD write-up. A future update on the
High Wind Warning is forthcoming. Over southeast Prince William
Sound, a nearly stationary trough will reinforce the pressure
gradient south of Copper River Basin leading to gusty winds up to
45 mph along Cordova and southeast Prince William Sound through at
least Thursday night. Very cold wind chills as low as -45F to
-55F and sustained winds of 35 to 55 mph are expected along
Thompson Pass tonight through Wednesday afternoon. For that, a
Wind Chill Advisory remains in effect for Thompson Pass. The
potential for blowing snow in areas where winds are 25 mph or more
will be closely monitored, with the potential of light snow
occurring near the trough axis as well.

At Kodiak Island, steady light snow and gap winds will persist.
Isolated troughs combined with upper level troughs passing
through Kodiak Island and Shelikof Strait will enhance increased
cloudiness and snow over Kodiak Island into Thursday afternoon.
About 2 to 4 inches of snow is expected for Kodiak City and along
the coast through early Thursday morning with much higher amounts
inland and at higher elevations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Tonight
through Friday)...

Southwest will remain under generally weak upper-level flow this
evening and through the next couple of days with high pressure
centered over the northern Bering and low pressure south of the
Aleutian Chain. This should promote generally clear and dry
conditions through Friday. Previous wind chill advisories for the
Lower Kuskokwim Valley and interior Bristol Bay have expired as as
winds gradually diminish and little additional cold air advection
is forecast. Into the next few days temperatures will fluctuate
little with arctic air not expected to return to Southwest until
the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3:
Tonight through Friday)...

Easterly flow will persist over the Alaska Peninsula and
Aleutians tonight into Wednesday as the Aleutian Chain remains
between high pressure over the northern Bering and low pressure
over the North Pacific. Evening satellite shows a weak area of low
pressure within this flow, which is overspreading the Eastern
Aleutians with areas of gale force winds noted from Cape Sarichef
westward to Nikolski. Easterly gales will increase in coverage
into Wednesday as a North Pacific upper low lifts northward into
the Bering and a west-to-east oriented and occluded front
approaches the Alaska Peninsula. Models suggest storm force gales
will develop south of the Alaska Peninsula by midday on Wednesday
before spreading north of the Aleutians through Wednesday night.
ALso to be expected with the frontal system's passage, a mix of
rain and snow are forecast across the Aleutian Chain and Alaska
Peninsula tonight into Wednesday. Southerly warm air advection
will eventually transition snow to all rain by Wednesday night.

However, as quickly as one upper low departs the Bering, a second
upper low is forecast to amplify over the Western Aleutians on
Thursday morning with an upper trough to bring another round of
showers and warm air advection across the Aleutians and Alaska
Peninsula into Thursday night. Further ahead, Friday looks to see
a brief reprieve in unsettled conditions until a new frontal
system makes its way into the Aleutians and Alaska Peninsula over
the weekend.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...

Bering/Aleutians... Broad Arctic high pressure combines with an
elongated area of low pressure South of the Aleutians through
Sunday. Forecast confidence remains high. Easterly gale force
winds spread over the Aleutians and Bering through Sunday. Seas
building to 22 feet over the Western and Central Bering for
Saturday and Sunday. Increasing risks for Freezing Spray as winds
become more Northeasterly for Sunday.

Gulf of Alaska... A trough across the Northern Gulf yields to an
approaching low and front through Sunday. Forecast confidence
decreases with the low and frontal placement. Boundary jets
increase to gale force along the Gulf Coast Saturday. The low
spreads gale force winds over the Gulf with areas of storm force
along the North Gulf and Alaska Peninsula coasts, and lower Cook
Inlet through Shelikof Strait late Saturday into Sunday. Seas to
20 feet along the North Gulf Coast on Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...

A pattern change is expected during the extended period as the
Aleutian Low will deepen across the central North Pacific. There
is a high degree of ensemble agreement with respect to the
placement and intensity of synoptic scale features at both the
surface and in the upper levels. Moreover, there is a very low
degree of ensemble spread with respect to the position and
intensity of the Aleutian Low. The strengthening Aleutian Low will
allow for a greater chance of precipitation across Southcentral
Alaska due to the geostrophic wind component to be from the south-
southeast off the Gulf (onshore flow). However, the ageostrophic
component to the wind (pressure gradient driven) will be north-
northeast (offshore) due to high pressure over the Alaska Interior
and Yukon Territory while this Aleutian Low deepens. This north-
northeasterly component to the wind will allow for the cold
temperatures to remain across Southcentral for the extended period
and increase the likelihood the predominant precipitation type is
snow. The best chance for precipitation across Southcentral will
be Saturday night through Sunday evening as a front moves across
the area. Forecast temperatures are expected to remain cold enough
for snow as the precipitation type across the Anchorage Bowl and
Matanuska Valley. The precipitation type forecast will be more
challenging across the lower lying coastal locations on the
windward side of the mountains due to warmer surface temperatures.
The highest precipitation amounts are expected to be across the
windward locations south of the Kenai and Chugach Mountains
(southern Kenai Peninsula and Prince William Sound).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory: 131.
         High Wind Warning: 111.
MARINE...Gale Warning: 130, 132, 138-139, 150, 155, 165, 170-180,
		 185, 352, 411-413
		 Heavy Freezing Spray: 119, 126-128, 130, 139, 141, 165,
		 179, 185, 412
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
MARINE/LONG TERM...KZ/ED