Small Craft Advisory 204, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKST Fri Mar 9 2018

.ANALYSIS AND UPPER LEVELS...
The main low over the area that has brought large amounts of snow
to the Kenai peninsula is south of Seward as it continues its
track toward Cook Inlet. The cold air wrapping into this system
has also cut off the warm air and is keeping precip as snow along
the north Gulf coast. Out west, cold, northerly flow dominates
with widespread snow showers.

&&

.MODEL DISCUSSION...
The models are still struggling with the western Gulf low which
raises uncertainty in the short term. The 06Z NAM initialized the
best so it was preferred for the short term. Guidance does not get
much better moving into the mid term with widely varying positions
of a low tracking into the Gulf Saturday night into Sunday. That
being said, the 06Z NAM took a jump from its 00Z run and is now
much closer to the GFS. Meanwhile, the EC is significantly faster
while the GEM lags behind lowering confidence in the mid term as
well.

&&

.AVIATION...
PANC...Northerly surface winds will continue into the afternoon
with Turnagain Arm winds bringing in a southeasterly wind aloft
resulting in low level wind shear. In the afternoon surface winds
should shift to the southeast and cut off the wind shear. There is
high confidence that the surface winds will shift to the
southeast, but there remains some question as to exactly when.
Then in the evening winds will slacken for the remainder of the
TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The strong low just southeast of the Kenai Peninsula is now slowly
tracking back to the northwest where it will quickly weaken as it
moves over Cook Inlet this afternoon and evening.

The most significant weather with this system continues to be in
the eastern Kenai Peninsula where heavy snowfall fell overnight.
While there is a brief lull early this morning there, the low
center moving over the area will bring in more snow through the
day and with blowing snow also a concern especially during the
morning. While the expected snowfall is not quite up to typical
criteria for a winter storm warning for that zone, the warning was
continued. A large part of this reasoning is the blowing snow this
morning and the additional snowfall throughout the day will make
travel through the Seward Highway...especially from Turnagain Pass
to Moose Pass very difficult. Snowfall overnight from some SNOTEL
stations in the area and the snow stake in Turnagain Pass show
accumulations in the 18 to 24 inch range since late yesterday
afternoon. Be aware that even after the warning expires this
afternoon, persistent snow showers with some heavy at times, will
continue over the eastern Kenai Peninsula through Saturday.

Anchorage, the Mat-SU valleys and the western Kenai Peninsula
will mostly have the downslope cutting off the snowfall with just
a few snow showers making it through. The track of the low looks
like it will also bring some southeast winds into Anchorage this
afternoon which will cause temperatures to jump into the mid 30s
to lower 40s before dropping again late this evening. The
Matanuska Valley will see a similar situation with the southeast
winds kicking in and increasing temperatures.

&&

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

The prolonged snow event which brought heavy snow to the region
is slowly beginning to wind down. Some of the early snowfall
totals just from yesterday afternoon were quite impressive, with
King Salmon having reported 17 inches and Iliamna reporting 18
inches. Both stations still had heavy snowfall occurring at the
time of these reports yesterday afternoon. For King Salmon, this
marks the highest two day total since 1993, and the sixth highest
total for 48 hours ever reported.

The storm which brought the heavy snowfall continues to slowly
fill and weaken, with it currently located south of Prince William
Sound earlier this morning. As the storm moves towards the
central Cook Inlet and then to the Iliamna area, wrap around
areas of snow or snow showers will continue through the day, with
additional light accumulations likely. Otherwise, a short-wave
ridge of high pressure will build across southwest Alaska for your
Saturday, bringing a brief period of clearing skies and drier
conditions.

&&

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

Winds will continue to decrease through the day as the storm
system which brought the strong winds and snow squalls continues
to slowly weaken. In its wake look for a fast moving narrow ridge
of high pressure to traverse the region from west to east,
allowing for a decrease in snow shower coverage as skies clear
some. This will be short-lived however, as another system enters
the western Bering and Aleutian chain by late evening/overnight
tonight, moving rapidly east during your day tomorrow. Winds and
precipitation will once again increase as the front approaches,
with precipitation becoming more showery in the wake of a cold
frontal passage. Once again snow will be the predominant
precipitation type, but some warm air may sneak into western to
perhaps west central portions of the Bering, and for most of the
Aleutian chain.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast is dominated by a trough of low pressure
that stretches from northwestern Alaska, to well southeast of
Kodiak Island. This trough will eventually get pinched off as a
weak wave slides in from the west. A lot of the action and
uncertainty evolve from the jet rounding the base of this trough.
While the small scale details are still uncertain, we can expect
one, or a few lows to move north and along the SE panhandle
Sunday and into Monday. Flow looks to remain supportive for no
precipitation for the Anchorage Bowl through this time. Chances
for snow may increase again next week as a front moves through the
area Monday/Tuesday. Due to a large spread in the models, WPC
guidance focused entirely on ensemble means, with no influence
from any operational members as we move into the middle of next
week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning...125.
MARINE...Gales...119 120 125 130 131 132 138 155 160 165 170 171
				 172 173 174 175 176 177 178 179 180 181 185 351
				 352 411 412 413 414.
		 Heavy Freezing Spray...160 180 181 185.

&&

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

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