Small Craft Advisory 199, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKST Tue Mar 6 2018

.ANALYSIS AND UPPER LEVELS...
An upper trough and associated weather front are moving east
across Southwest Alaska and Bristol Bay. The heavier snow at noon
today was clearing eastern Bristol Bay. The Kenai Radar showed
increased reflectivity returns across Cook Inlet and the Kenai
Peninsula. Snow has started over the Cook Inlet and the Western
Kenai Peninsula and is heading north. Pressure rising on the
backside of the front generated gusty southwest winds across much
of the Southwest Mainland. Brisk and gusty southwest winds were
evident across much of the Aleutians and the Bering Sea.

&&

.MODEL DISCUSSION...
Synoptic level features are in general agreement through
Wednesday night. The GFS/ECMWF looks to be the preferred solutions
in the Bering Sea/Southwest Alaska through Thursday. 12z models
differ significantly with the handling of the triple point which
heads toward Southcentral on Thursday. The run to run trend has
been to take the surface low further west. See long term
discussion for further details.

&&

.AVIATION...
PANC...MVFR to IFR conditions in snow and stratus are expected to
develop by early evening and continue into Wednesday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The remnants of a frontal boundary have moved into Southcentral.
The upper level trough that is driving this system has already
become negatively-tilted. Both the radars at Middleton Island
(PAIH) and Kenai (PAHG) have pinged into bands of precipitation.
The ASOS at Homer has already recorded snow this afternoon. The
models continue to depict the moisture moving up Cook Inlet and
into the Anchorage Metro Area and the Mat-Su valleys. Generally
expecting 1-3 inches of fresh snow to blanket the region this
evening and overnight. This system is shaping up to be an all snow
event for Southcentral although its possible that some random
location in Prince William Sound may get a rain/snow mix with the
water temperature impacting the lowest levels of the boundary
layer. This is a quick moving storm and will move east of
Anchorage by Wednesday morning becoming an issue for Valdez.
Wednesday ridging will build back into the region from the southwest.
Which will be the quiet before the storm. The models continue to
spin up another low later in the week but the solutions are not in
sync yet. Stay tuned for more details.

&&

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

A progressive wave pattern continues to impact Southwest as
another shortwave trough and associated front moves through the
region. Onshore westerly flow behind the front which moved through
earlier is leaving snow showers over the Kuskokwim Delta and Lower
Kuskokwim Valley. As the winds weaken this evening, and clouds
break up, fog is expected to increase and possibly become locally
dense. The next, and more significant front, moves into Southwest
Wednesday and Wednesday night. This will bring widespread snow to
interior Southwest (mixing with some rain along the immediate
coast). Accumulations will be highest along and near the
Alaska/Aleutian Ranges, especially from east of King Salmon north
to Iliamna and Port Alsworth. Snow accumulations through Thursday
may upwards of 6", but track of the low Thursday evening and night
remains uncertain. Should it even go slightly eastward, the total
snow accumulations will drop significantly. For now, a middle
ground approach was favored for this forecast.

&&

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

A storm force low will move into the Bering Sea tonight and last
through Thursday night. Most of the Bering Sea will see maximum
gale force winds with storm force winds relegated to the northern
Bering Sea. The low will track east Thursday, and will begin
tapping colder arctic air coming off of Eastern Siberia. This will
bring a swath of strong northwest gales and snow showers and
threats for freezing spray.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The latter half of this week will be marked by a rapidly
developing strong storm system that will develop near Kodiak
Island on Thursday and move to somewhere near the Kenai Peninsula
Thursday night and Friday. As always, the exact track of the low
will make all the difference for the locations prone to
downsloping like Anchorage and the Matanuska Valley. There is
definitely potential for the seasons biggest snowfall somewhere in
the Cook Inlet area, but recent models trends have shifted the
heaviest snow over the western Susitna Valley and perhaps even the
western Kenai Peninsula, while the Anchorage and Palmer areas
would see much lower amounts. Stay tuned over the next 24 hours,
as hopefully the models will come into much better agreement and
we can start refining some of the forecast details for this storm.

For the start of the weekend, a generally showery and unstable
airmass over the Gulf will keep showers mainly along the coast,
while much of the Bering Sea remains under high pressure and
quiescent weather. Another weather front moves into the western
Bering Sea Saturday evening but looks at this point like it will
fall apart significantly by the time in reaches the Southwest
Mainland on Monday. Model agreement falls apart significantly from
Monday onward, though in general it looks like the progressive
southwest-to-northeast storm track of the last few weeks will
continue, with periodic chances for snow/active weather across
most of the forecast domain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 185.
         Gale 172 173 174 175 176 177 178 179 181.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...AMD