Small Craft Advisory 207, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
426 AM AKST Sat Mar 10 2018

.ANALYSIS AND UPPER LEVELS...
A broad longwave trough extends through mainland Alaska and the
western Gulf. This setup is bringing southerly flow and showers to
the north Gulf coast. Out west, ridging has built in over the
western Bering bringing warm air from the south with it.

&&

.MODEL DISCUSSION...
The models continue to struggle in this active pattern. This is
particularly true for the east side with multiple lows moving
through the Gulf. So while there is high confidence with an active
pattern bringing multiple lows through the area, there is
uncertainty with how the lows will move through and the impacts
they may have.

&&

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

&&

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

Snow showers...some heavy...will persist over the eastern Kenai
Peninsula today, but be gradually tapering off during the
evening. The Winter Storm Warning has been cancelled. Due to
backcountry avalanche danger through the weekend, a Special
Weather Statement to relay information from The Chugach National
Forest Avalanche Center has been issued.

The rest of the north Gulf coast will continue to see snow showers
today and the showers will also taper off by tonight. Most of
the remainder of Southcentral will just see a few snow showers
spill over the mountains but POPs are generally low inland.

The next weather system to watch is expected to move into eastern
Prince William Sound Sunday and spread westward Sunday night.
Model tracks are still a bit uncertain but the Prince William
Sounds region will likely see some more snow with the heaviest
amounts being in the eastern Sound this time.

&&

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

Winds continue to weaken this morning as the pressure gradient
weakens, due to the main storm system having reformed further
south in the Gulf due to jet stream energy diving into the trough
while deepening it further, causing a further south low position.
With this in mind, the blowing snow advisory for the Kuskokwim
Delta has expired. Brief ridging will cross the area tonight into
tomorrow morning. As the ridge axis passes overhead, weak warm
advection will help steepen a low-level inversion, aided by the
recent snowfall. This should promote a fairly expansive stratus
deck with some fog developing.

Our attention then turns to a fast approaching front for the day
Sunday. Southeasterly winds will increase ahead of the front,
mainly near the coast and at higher elevations. This could promote
some areas of blowing snow. However, with the recent snow having
compacted some and typically southeast winds bring a wetter
snowflake production, how much blowing snow will develop remains
questionable enough not to include in the forecast at this time.
As the front crosses the region snowfall coverage will be fairly
widespread with bursts of moderate intensity snowfall possible.
However, accumulations don't look to be to significant with just a
few inches expected.

&&

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

The snow shower activity that has plagued the eastern two thirds
of the Bering and Aleutians the past few days will continue to
diminish through the morning, as a fast-moving narrow ridge of
high pressure builds across the region, moving from its current
position across the western central portions of the Bering/chain
to the coast of southwest Alaska by tomorrow morning. Quickly
following on its heals will be a cold front currently entering the
western portions of the region. As it moves from west to east, a
deepening low off the Siberian coast will increase warm advection
ahead of the incoming front, with a warm front surging through the
Aleutians into the north central portions of the Bering. This
will allow precipitation to change from snow to rain following
the warm frontal passage, mainly south and west of a line from
Siberia, through the Pribilof Islands, towards Nelson Lagoon.

As for the winds ahead of the fronts, some spotty sustained gales
may develop along the warm front across the eastern Bering, with
the better chance being immediately ahead of the cold front and
near the Aleutians from Nikolski westward. Otherwise, winds will
remain below gale criteria. After cold frontal passage, colder
air filtering back into the region will allow precipitation to
become more showery in nature, with snow showers being the
predominant precipitation type.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast begins Monday with a deep but narrow upper
level long wave trough bisecting mainland Alaska and extending
south to nearly 30N. A surface low will move from the Northern
Gulf into the Prince William Sound bringing another round of snow
to coastal areas and the mountains, though the inland areas west
of the Kenai and Chugach Mountains look to remain mostly snow free
as the bulk of the moisture and energy should remain far enough
east.

A progressive pattern will continue across the region as we
head into the middle of next week as a strong westerly jet moves
over the Aleutians and pinches off the upper level low well to the
south of our area. Temporary ridging will build in over the
southern mainland Tuesday and Wednesday morning bringing a short
break in the stormy pattern before another trough digs in across
the Eastern Bering spinning up another low that looks to move
across Western Alaska and eventually Southcentral by Thursday.
The models begin to diverge some at this point with the track of
the low center but all agree that a decent amount of moisture will
be associated with this system aided by a strong southerly upper
level jet pumping moisture in from the North Pacific. This storm
also looks to be a bit warmer than the previous ones we've seen
the past couple of weeks meaning precipitation types could be
challenging with rain possibly mixing in with snow at sea level
locations. Stay tuned as details become clearer regarding this
system next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...174 175 176 177 178 351 352.
		 Heavy Freezing Spray...160 180 181 185.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
237 PM AKST Sat Mar 10 2018

AKZ125-120200-
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood,
and Moose Pass
237 PM AKST Sat Mar 10 2018

...Special Avalanche Bulletin...
  
Bulletin - Immediate Broadcast Requested

The following message is transmitted at the request of the
Chugach National Forest Avalanche Center -

The Chugach National Forest Avalanche Center in Girdwood AK has
issued a Special Avalanche Bulletin.  

* Timing...In effect now through 6 pm Sunday March 11th, 2018.  

* Affected Areas...For Turnagain Pass and areas in and around
  Eastern Turnagain Arm, including the Kenai and Western Chugach
  Mountains.  

* Avalanche Danger...Dangerous avalanche conditions will exist
  through the weekend due to 2-4 feet of snow that has fallen on
  an unstable base. Human triggered large avalanches are likely on
  slopes steeper than 30 degrees.  

Precautionary/Preparedness Actions...

Choose terrain that is flat or less than 30 degrees in steepness,
with nothing steeper above you. If skies clear for travel into
the alpine elevations, careful snowpack evaluation, cautious
route-finding and conservative decision making skills will be
necessary to identify and avoid unstable slopes.

Similar avalanche danger may exist at locations outside the
coverage area of any avalanche center. Check www.avalanche.org 
for your closest avalanche center and to learn more about how to
learn about how to identify avalanche hazards.

This Special Bulletin does not apply to ski areas or highways
where avalanche reduction measures are performed.