Small Craft Advisory 251, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKDT Sat Mar 24 2018

.ANALYSIS AND UPPER LEVELS...
While the upper level ridge that has been over the mainland part
of the state this week has weakened, it still persists over the
area. The upper level anchor low remains over eastern Russia to
the west-northwest of the Gulf of Anadyr with a digging trough in
the central Bering Sea. The surface low in the central Bering Sea,
and the associated front entering southwest mainland Alaska, are
still progressing eastward but slowing down as they push into the
ridge of high pressure over the state.

&&

.MODEL DISCUSSION...
Models are in better overall agreement for the early part of next
week than previous runs. The discrepancy in tracks for the
eastern Bering sea system on Monday has closed significantly.
Models are also taking a more northerly course which better
reflects what the GFS was showing yesterday. In the Gulf of Alaska
the 12Z ECMWF run has veered farther north and now is showing a
similar track along the north Gulf coast that the NAM and GFS have
been depicting.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sun and
Mon)...
One weak surface low located over the NE Gulf of AK is pulling
away as a stronger front will work into the area Sun. First, the
low in the Gulf is keeping some minor gusts through the typical
outflow locations such as Seward and Whittier. But as the low
moves away and weak ridging builds in overnight, these winds will
continue to diminish. There is an outside shot that the western
Kenai Peninsula could see some patchy fog tonight with increasing
stability and light winds.

Sunday will start out with continued quiet weather across most of
the domain. However, attention will quickly shift to the front
approaching from the southwest. This front will impact Kodiak
first. Precipitation could start as snow, but with flow off the
Gulf and warm air advection associated with it, things should
quickly mix and turn over to rain, especially at sea level. The
initial front then slows and starts to fall apart before it really
reaches the Gulf Coast (Kenai Peninsula and Prince William
Sound). Another piece of energy will move in quickly from the West
Sun afternoon reinvigorating the front and aiding in the
formation of a triple point surface low just east of Kodiak late
Sun evening. Models have trended further south with this feature
today. This will mean a slightly stronger offshore gradient along
Coastal areas. This gradient will pull drier air from the mainland
and take a bite out of precipitation along the front. Thus, have
trimmed PoPs back from inland areas even more and certainly
lowered the QPF. The front still looks on track to bring some
gusty east-southeast winds through the Turnagain Arm and Portage
Valley. However, because of the triple-point low, down-inlet flow
will keep these winds from making their way into Anchorage.
Precipitation still looks unlikely across inland population
centers due to cross- barrier flow. Any accumulating snow
continues to be confined to coastal areas and limited to just a
few inches with near-freezing surface temperatures.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level trough will begin to push into Southwest Alaska
this evening, along with a frontal system from the eastern Bering
overnight tonight. Light to moderate snowfall is expected to start
Sunday morning along the coast of Bristol Bay and the Kuskokwim
Delta, then pushing inland through Monday when things become more
showery. The greater Bristol Bay area looks in the best position
to pick up the most snow with this system with areas of blowing
snow developing in the locations with stronger east southeasterly
winds, particularly downwind of gaps in the Alaska/Aleutian Range.
A Winter Weather Advisory has been issued for the Dillingham
North and West areas from Sunday morning through early Monday
morning, with 3 to 6 inches of snow expected (localized amounts up
to 10 inches), gusty winds up 40 mph, and reduced visibilities
down to a half mile or less at times.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The area of low pressure over the central Bering will continue to
deepen as it tracks to the east northeast through the remainder of
the weekend, arriving just to the north of the Pribilof Islands
Sunday afternoon or evening at its maximum depth. The low will
become vertically stacked at this point and will continue slowly
move on to the east northeast arriving along the Kuskokwim Delta
Coast Tuesday morning. To the west of this broad low, northwest
flow will spread cold air and showery conditions across the
western portion of the Bering through Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Model consistency in the long range has not improved since
yesterday. The first challenge is the location of the weak low
that will move onto the North Gulf Coast on Monday. This system
is not strong enough to bring the winds to gale force, however a
difference in the location could bring up to a 180 degree change
in wind direction along the Gulf Coast. For consistency, the Day 3
forecast was not changed significantly in this area. The second
issue of concern is the stronger system moving into the Gulf of
Alaska on Wednesday/Wednesday night. Although models are still in
agreement about a low pressure system moving into the Gulf, the
track and strength still vary greatly from model to model and run
to run. Currently EC/Canadian seem to be the closest in solution,
bringing the low northward into the center of the Gulf, while the
GFS shunts it off toward the Panhandle. Given the fact that the
GFS is the outlier, a northerly trajectory of this low seems most
likely. The main difference this will make in the sensible weather
is for the Gulf of Alaska, where winds may strengthen to gale
force Thursday and Thursday night. As for Southcentral, Southwest,
and the Bering, the building ridge continues with the promise of
good weather for the end of next week. &&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 161.
MARINE...Gales 120 131 173 175 180 181 412-414.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...LF