Small Craft Advisory 159, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 AM AKST Mon Feb 19 2018

.ANALYSIS AND UPPER LEVELS...
A high amplitude ridge has reasserted itself over the Alaska
mainland this morning as the remnants of a weak trough that
brought light snow to southcentral yesterday rapidly moves east
towards the ALCAN border. Skies are clearing rapidly behind the
front over southcentral though a stubborn stratus deck has
remained over the Cook Inlet/Knik Arm area with low clouds
covering the Anchorage Bowl and the Matanuska Valley. A strong
southerly jet over the Central Bering is supporting a storm force
surface low currently centered near the Gulf of Anadyr with a
front extending far out ahead of it moving east across the Eastern
Aleutians. This front is bringing warm moist air, with
temperatures climbing into the 40's, as well as strong winds to
the Aleutians/Bering.

&&

.MODEL DISCUSSION...
Models are in good agreement this morning showing a persistent
ridge building in over the eastern half of the state with a front moving
across the Bering and into SW Alaska Monday night before being
sheared apart as it runs into the ridge, keeping Southcentral
mostly dry. Models begin to differ some on Thursday as a
subsequent, more potent system comes barreling across the state.
The GFS/NAM are a bit quicker than the EC/Canadian solutions, but
all agree that this system will break the ridge down some allowing
snow to make its way into southcentral by at least Thursday
night.

&&

.AVIATION...
PANC...Stratus has stuck around the Anchorage Bowl this morning
with predominate MVFR conditions expected with some intermittent
lower IFR Cigs building in, as seen in nearby METARS. An upper
level ridge axis will move over Anchorage today which should help
to scatter out the low clouds this afternoon, at least directly
over the terminal. The ridge axis though, with strong subsidence,
clearing skies, and weak flow, will again favor the development of
low stratus and fog tonight and into tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will build over Southcentral Alaska today. Some
stratus remains over the Cook inlet area this morning, which
should break up this afternoon. This ridge will remain over the
area through Tuesday night. A weak upper level trough will briefly
lower heights with the ridge as it traverses the area on Tuesday.
Although this system is fairly dry, some precipitation is possible
in the morning from about Anchorage northward, as well as over
the Copper River basin from late morning into the early afternoon.
This will also weaken the low level offshore gradient. Upper
level heights then increase as the the ridge rebounds Tuesday and
Tuesday night.

&&

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

A powerful storm force low over the western Bering Sea is
supporting a strong cold front over the eastern Bering Sea--this
front is currently tracking toward the coast. Strong southerly
winds ahead of this front are already gusting into the 40-45 MPH
range and will remain strong through early morning. The front
will then move inland through tonight, bringing rain and snow to
all of Southwest Alaska, although any accumulations will be minor
as the front will quickly weaken as it moves inland. High pressure
settles in for Tuesday before a warm moves into the Kuskokwim
Delta, bringing another shot of rain/snow as the progressive wave
pattern continues.

&&

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

A strong 959 mb low is currently taking shape over the Bering Sea
this morning. Early morning scatterometer satellite passes have
captured near storm force winds over the far southwest Bering Sea,
and this low is expected to strengthen to storm force today as
cold air advection wraps around the surface low. Sea states are
still expected to reach near 40 ft over the northwestern Bering
Sea as the low tracks northward. The gale force front will clear
the Eastern Aleutians by tonight with brief high pressure settling
over the Bering. The next weaker gale force low will move into the
Bering Tuesday and will lift north through Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The general trend for the long term forecast beginning the middle
of this week will be for continued active weather moving from the
Bering through the Mainland into next weekend. This will be
produced by a flattening the ridge that has setup over the North
Pacific, allowing for a broad westerly jet to stretch from the
Aleutians through the Mainland and into British Columbia. This
pattern will bring a series of Bering systems to begin impacting
the South Mainland with chances for rain and snow, the first looks
to move through late Wednesday into Thursday. After this system
passes through model agreement begins to decrease significantly
with the track of the upper level low over the Western Bering and
how it interacts with the the North Pacific ridge. As a result the
forecast uses ensemble guidance heavily starting Friday, leading
to a broad brushed and generally low confidence forecast for most
of the area through next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 185.
Gale Warning 165 170 173 174 175 176 177 178 179 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DEK/SEB