Small Craft Advisory 146, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKST Tue Feb 13 2018

.ANALYSIS AND UPPER LEVELS...
The upper level ridge has amplified over mainland Alaska today
with the axis running near the Alaska Range and into the Interior
of the state. The deep upper level low centered near the Kamchatka
Peninsula has a front which is pushing into the ridge bringing the
snow into the Kuskokwim Delta and Kuskokwim Valley. A weak upper
level wave is located just a little west of the ridge axis and
will move over the Cook Inlet and Mat-Su regions tomorrow morning.

&&

.MODEL DISCUSSION...
The 12Z and 18Z model runs have really come together nicely for
the low moving into the Bering Sea Thursday into Friday. That was
the issue with model runs over the previous few days and looks to
be resolving. The next issue comes in this weekend over the
Bering Sea but all models still show the ridge holding firm over
the eastern half of mainland Alaska Saturday and moving into the
Yukon on Sunday.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through the
night. There may be a brief MVFR ceiling tomorrow morning with a
shot of light snowfall moving through, but this is not expected to
last long if it does occur.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level ridge will remain over the area tonight for
continued dry conditions. Fog looks unlikely with increasing high
and mid level clouds. Offshore flow will weaken as the surface
gradient relaxes. A weak upper level short-wave trough will cross
the ridge on Wednesday. This will provide a chance or slight
chance of snow over much of the area. Snow is likely from about
Talkeetna northward with slightly better dynamics than the rest of
Southcentral. The upper level ridge will quickly rebound
Wednesday night and Thursday for a return to dry and mostly clear
conditions. The surface gradient will not be very strong, and thus
offshore winds will not be very strong. A weather front will
approach Kodiak Island from the southwest late Thursday night,
with a chance of precipitation developing on the south end of the
Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Wednesday and
Thursday)...

A front stretching from near Nunivak Island to just east of the
Pribilofs and down to Dutch Harbor this afternoon continues to
spread light precipitation across portions of Southwest Alaska
ahead of it. As the front weakens, precipitation rates over the
Kuskokwim Delta, Lower Kuskokwim Valley, and south through Togiak
will gradually diminish with time overnight. Nevertheless, with
nightfall, cooler air should turn many areas back over to all snow
overnight, and an additional 1-3 inches of wet snow from Bethel
east is expected.

On Wednesday, the front will dissipate and move more quickly
east. Many areas of the Lower Kuskokwim Valley over to Bristol
Bay may see a few off-and-on snow showers with it, but no
accumulations of much significance are expected during the day. As
the front moves east, skies will clear somewhat behind the front,
and much of the day west of the Kuskokwim Mountains will feature
some sunshine.

Wednesday night, clearing skies and calm winds will allow
temperatures to drop quickly in the evening from Bristol Bay
northward. Because of the recent snowfall from the front, however,
areas of freezing fog are expected. On Thursday afternoon into the
overnight, another front oriented more southeast to northwest
will impact much of Southwest Alaska starting at the coast with
more light snowfall, with accumulations on the order of only a few
inches due to short duration.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Wednesday
and Thursday)...

The front over the eastern Bering will continue moving into
mainland Alaska tonight. Behind it, a much more convective
satellite regime is in place, making for a mix of clouds and sun
with plentiful snow showers, especially the further west you go.
The convective air mass will persist into Wednesday. The next low
begins moving into the western and central Aleutians near Adak
during the day Wednesday. The low will track north through the
central Bering, with gale force winds expected to either side of
the low. Storm force gusts are expected south and west of the low.
The associated front will move through the rest of the Bering and
into mainland Alaska by Thursday evening. Yet another front is
expected to move into the western Aleutians Thursday afternoon
bringing another round of mixed precipitation and gusty winds.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The weather pattern will be turning into a repeat scenario into
the weekend. Weak ridging will build across the southern mainland
Wednesday into Thursday. This system will be followed by an upper
level trough and attendant weak front sliding through the AKPEN.
A weak surface low is expected spin up along this front and slide
east along the northern Gulf of Alaska Friday. Before this low
exits across the panhandle, warm air will again invade areas
along the Chugach. This will be short lived as cooler air dives
south and replaces the warm air towards this weekend. In a similar
fashion leading into next week, another transient ridge will
slide across southern Alaska as another front is expected by mid
week and the similar up and down cycle of temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 170, 173, 174, 175, 176, 177, 179, 412, 413, 414.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...SS