Small Craft Advisory 958, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Sat Dec 3 2016

.ANALYSIS AND UPPER LEVELS...
With low pressure over the Gulf and cold air advection moving
through Southcentral Alaska there are widespread outflow winds
over Southcentral. Out over the eastern Bering, ridging is slowly
moving towards the west coast which is aiding in the cold
northerly flow over the state and helping to clear out cloud cover
over the southern mainland. Another low has moved in over the
western Bering with its associated front moving through the
Western Aleutians.

&&

.MODEL DISCUSSION...
The models are in decent agreement with the main synoptic
features. Even though they are handling the main features well
there are still some issue with timing and intensity of the
outflow winds, especially in channeled areas.

&&

.AVIATION...
PANC...Cold air advection is helping to create gusty outflow
winds over the area that look to last through the afternoon when
the cold air advection stops. However, the northerly winds will
continue into tomorrow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Offshore winds and cold advection will continue today and tonight
with a surface low pressure in the gulf and high pressure to the
north and west. Very strong winds are expected for Thompson Pass
and Valdez, especially tonight as the upper level flow becomes
more favorable. The cold air combined with gap winds along the
northern Alaska Range will drop wind chills to as low as -45
tonight and possibly Sunday night. The surface low centered over
the northeast gulf will slowly drift south through tonight then
quickly exit southeast Sunday and Sunday night. This will allow
the gradient to relax and the winds to diminish. The associated
upper low centered near the tip of the Kenai peninsula will drift
east-southeast through Sunday night.

Some lingering light showers are possible to the east of Cook
Inlet as cold advection pushes the moisture up against the
mountains. These should end later today as the air mass becomes
progressively drier. Some wrap-around moisture from the Gulf low
will produce some showers over the Copper River basin and eastern
Prince William Sound areas through tonight. Dry conditions are
then expected Sunday and Sunday night as the low exits the area.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Cold and dry conditions will persist through the weekend beneath
mostly clear skies as a high amplitude ridge builds over the
southwest mainland from the west. A tight pressure gradient will
continue to produce gusty winds along the Aleutian and Alaska
Ranges through tonight before diminishing on Sunday as the strong
gulf low departs to the southeast. Dry northerly flow will begin
to give way to easterly winds and increasing mid and high level
clouds along the coast on Sunday as the Bering front makes slow
eastward progress towards the mainland. However, any associated
precipitation is expected to remain offshore as the ridge cuts off
into a closed high and remains anchored over the northwest
mainland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Northerly flow and cold air advection will continue to produce
gale force winds and storm force gusts over the coastal waters to
the southwest of Kodiak Island through tonight on the backside of
the trough over the Gulf of Alaska. Scattered snow showers will
also continue across the Alaska Peninsula before the northerly
flow begins to weaken with the departure of the trough. Otherwise,
the strong front currently moving through the Western Bering will
be the primary feature of interest through the weekend as it
makes slow eastward progress across the Bering/Aleutians. The
front will bring storm force winds and potentially heavy
precipitation to Adak and Atka later today before moving towards
the Pribilof Island and Eastern Aleutians and gradually weakening
tonight into Sunday. Precipitation may begin as a rain/snow mix
with the arrival of the front, but should then quickly transition
to all rain as warm North Pacific air streams northward. Cold
advection behind the front will then bring scattered snow showers
to much of the Western and Central Bering by Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period Sunday evening, a deep arctic
trough will be moving southeast away from Alaska with a weaker
upper trough remaining over the state. However, with a weakening
pressure gradient and clearing skies, the remaining arctic airmass
will be good enough to result in some of the coldest temps of the
winter over Southcentral. Arctic troughing inland will weaken
Monday and Tuesday as a Bering low moves toward Kodiak Island with
increasing cloud cover and slowly warming temperatures aloft.
Offshore flow will remain in place, however, which will keep
temperatures well below average through midweek. Meanwhile, snow
and snow showers will move into parts of SOuthwest Alaska and
eventually the North Gulf Coast Monday night and Tuesday. Most of
the precipitation should remain along the coast across
Southcentral with downslope flow likely keeping inland locations
on the dry side. By late week, uncertainty grows, but with
blocking over the Arctic and ridging extending through the Bering
Sea, it is likely Southcentral will remain on the drier and colder
side as upper level north to northeast flow keeps an offshore
pressure gradient in place.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 131.
  Wind Chill Advisory 141 145.
MARINE...Storm Warning 130 131 132 138 175 176 177 185.
  Gale Warning 121 127 128 129 136 137 150 170 172 173 174 179
181.
  Heavy Frz Spray 129 130 138 140 160 180. &&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...DEK