Small Craft Advisory 219, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 PM AKDT Wed Mar 14 2018

.ANALYSIS AND UPPER LEVELS...
A broad deformation zone extending from the Northern Gulf to
across the MAT-SU Valleys continues a mixture of rain and snow
along the coast with snow inland. The zone has actually crept a
little to the West with light snow/flurries spreading to the
western Anchorage Bowl. A weak surface trough over the northern
Gulf gave rise with relatively weak but gusty outflow conditions
over the Eastern Kenai Peninsula and North Gulf Coast. Strong
winds however were evident with westerly gale gusts over the
Barren Island marine areas. Conditions were relatively
precipitation free over Southwest Alaska though there was an
abundance of low clouds and some patchy fog which developed in the
wake of an eastward moving trough. Surface ridging was the
dominate feature over the central and western Bering Sea.

&&

.MODEL DISCUSSION...
The Canadian Regional, ARW, and GFS20 models seem to be doing the
best job on the area of snowfall associated with the deformation
zone extending across the Chugach Mountains to the MAT-SU Valleys.
Trough passage tonight across Southcentral and onset of southerly
flow aloft Thursday are handled similarly between models. Out
west, models have come into better agreement with low heading
toward the Alaska Peninsula/Bristol Bay, though they struggle some
on low positioning Friday as the low gets into Bristol Bay. The
sensible weather however seems to be similar and reasonable.

&&

.AVIATION...
PANC...Generally VFR conditions tonight, though ceiling and
visibilities by briefly drop below during the early evening hours.
There is a chance that patchy fog may develop and impact the
airport complex Friday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Snow will linger along the Glenn Highway corridor from Eagle River
to Palmer this evening before coming to an end as the upper trough
lifts to the northeast through the Copper River Basin overnight.
This will bring a temporary break in precipitation for much of the
area through early Thursday before the next system approaches
rapidly from the southwest. Snow will first spread over Kodiak
Island Thursday morning and then quickly transition to rain by
afternoon. Precipitation will then spread to the remainder of
Southcentral Thursday evening into Friday morning. Warmer
temperatures will support a rain/snow mix for many coastal
locations, helping to limit accumulations to a few inches of wet
snow for these areas. Southeasterly flow in the low levels will
maintain an element of downslope flow from Anchorage into the Mat
Valley, however broad south to southwesterly flow aloft should be
enough to initiate some weak overrunning precipitation for these
areas. Any possible snow accumulations will thus be limited here as
well. Given the prolonged period of S-SW flow aloft, the best
snow potential will reside over the western and northern Susitna
Valley from Thursday night into Friday afternoon. Accumulations
are expected to remain below advisory thresholds at this time, but
will continue to evaluate that potential over the next 24 hrs.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A brief reprieve from snowy weather is underway and will continue
through tonight before the next system begins to push into the
area from the southeastern Bering Thursday morning. This system
will initially spread snow northward over much of the southwest
Mainland. Some areas over the Bristol Bay will moderate to a mix
of rain and snow Thursday, with some pockets of freezing rain
developing north of King Salmon Thursday night into early Friday
morning. Otherwise, expect this moisture rich system to bring
widespread snow to the remainder of the mainland through Friday
with Advisory level snow amounts from Dillingham North and West
Thursday, and over the lower Kuskokwim Valley Thursday night into
Friday morning. Also expect areas of blowing snow over the
Western Capes Thursday morning, and over the Kuskokwim Delta
Thursday afternoon into Friday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A more active weather regime is underway over the region as a
north Pacific low tracks northward toward the eastern Aleutians
tonight into Thursday, and another front begins to push into the
western Aleutians/Bering tonight. The front associated with the
north Pacific low will bring warmer temperatures, gusty winds,
and rain to the eastern half of the Aleutians through Friday. The
front out west will bring some rain and gusty winds over the
Western Aleutians/Bering tonight through Thursday morning. The
front will stall, elongate, and weaken Thursday afternoon, keeping
some showery conditions lingering over the area before the next
system moves into the area on Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long range forecast begins Saturday with a broad upper level
trough that is slowly pushing east through the Bering. With this
feature there will be a few rounds of precipitation that'll hit
the west coast and spread inland. The first is well handled by all
guidance and will involve a surface low with an attendant front
lifting through the Bering Strait. A second, and stronger
shortwave will round the base of the trough and shoot towards SW
Alaska Sunday afternoon. It is here that models begin to fall
apart. National Centers prefer more of a focus on the operational
EC than the GFS due to run to run continuity. On Sunday, a second
low will repeat the motions of the first low, but push farther
inland this time. This may help to bring a chance for snow early
in the week for southcentral Alaska.

Around this time, a strong ridge will begin to build across the
Bering Sea. It is expect to strengthen through mid week but stall
over the AKPEN by Wednesday. This ridge will get pinched off by a
strong Pacific jet that will dive south of 40N. Most of the area
should see northerly winds through this time. For the Anchorage
Bowl, temperatures will be near normal. Sunny skies will help to
make it feel warmer and melt some of the lingering road ice
through mid week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blowing Snow Advisory 155
         Snow advisory 152 161
MARINE...Heavy Freezing Spray Warning 180
         Gale Warning 155 160 170 173 174 176 178

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...SS