Small Craft Advisory 170, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 PM AKST Thu Feb 22 2018

.ANALYSIS AND UPPER LEVELS...
A frontal zone is moving rapidly eastward across the Cook Inlet to
MAT-SU Valley corridor this afternoon. This trough is actually
moving a little faster than model projections. Lower clouds
however are lingering over Cook Inlet and the eastern Kenai
Peninsula. Snow and mix are falling across the north Gulf Coast
with snow over the Copper River Basin. Outflow conditions are
developing over western Cook Inlet and the western Gulf with
pressure rises on the backside of the front.

Further West, brisk westerly winds with isolated snow showers are
evident over Southwest Alaska as the surface trough lifts north. A
strong front approaching the western and central Aleutians is
generating southeasterly gales and rain along the central and
western Aleutians.

&&

.MODEL DISCUSSION...
Models overall are in good agreement across Southcentral. The
main difference are QPF values across Cook Inlet to MAT-SU
corridor with the front Friday night/Saturday. Will lean toward a
middle ground approach for now. Out west, models are in fairly
good agreement through Friday morning then significant
differences arise in the placement of low centers with a trough
axis stretching west to east across the northern and central
Bering Sea. Will lean in general toward the GFS.

&&

.AVIATION...
PANC...except for the brief period of VFR conditions this
evening. Ceilings and or visibilities will be MVFR/IFR . LIFR
conditions in fog and stratus likely after midnight and should
hold through the morning hours Friday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Snow showers are tapering off from west to east this afternoon as
an upper level trough sweeps across southcentral Alaska with snow
expected to last the longest in the Copper River Basin. The
accompanying surface low located south of Prince William Sound
will continue east across the northern Gulf this evening. Westerly
winds will increase rapidly behind this low, particularly through
gaps and channeled terrain such as the Barren Islands and Passage
Canal with strong northerly winds funneling through Resurrection
Bay. The next frontal system will reach Kodiak Island Friday
afternoon or evening and then lift north over the Kenai Peninsula
and into southcentral Alaska Friday night through Saturday
morning. With an upper trough and strong cold air advection
following this low, expect snow to liquid water ratios to be quite
high (producing light fluffy snow) with orographically enhanced
cold advection snow showers persisting along the mountains through
at least Saturday afternoon or evening.

&&

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

Gusty west winds will diminish tonight as ridging moves into the
area from the Bering Sea. Combined with the onset of weak warm air
advection, fog or at least low cloudiness is likely to redevelop
across much of the area by Friday morning. By Friday afternoon, the
next storm will make landfall across the area. Temperatures will
warm up but the majority of the area should remain cold enough to
stay snow with several inches accumulating by Saturday morning.
The snow will be low density over most of the Kuskokwim Delta,
where the east winds will also linger the longest. A blowing snow
advisory is in effect from Nunivak Island northward starting
Friday afternoon. By Saturday, winds will switch around to breezy
west winds once again across the area as clouds clear and sun
breaks emerge. These gusty west winds will continue through much
of the weekend, and allow some rough surf to develop along the
coastlines Friday night through Saturday night.

&&

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

The next storm front has passed Shemya and is progressing
eastward. This storm will cross the Bering Sea in fairly rapid
fashion tonight and tomorrow with gale-force winds and widespread
rain. Once this front exits the area, the parent low will stall
for the next few days over the northern Bering Sea, which will
allow long-fetch westerly gales to set up over almost the entire
area through the first half of the weekend. This will allow fairly
significant wave run-ups over the eastern 2/3 of the Bering,
which will combine with widespread snow shower activity to impact
most locations from the Pribilofs to the eastern 1/2 of the
Aleutians with unsettled weather.

&&

.LONG TERM FORECAST (Sunday through Thursday)... The active and
progressive pattern will continue Sunday through Thursday. This
means we will see another snow producing system departing the
southern mainland Sunday morning followed by weak ridging to see
yet another upper trough and the resultant surface feature move
through the southern mainland again late Sunday and Monday. By
Thursday a large low with a front from the northern Bering draping
through the western mainland will likely bring strong warm
advection into the mainland Thursday. However, south central
Alaska will remain on the cooler side keeping precipitation frozen
inland.

Over the Bering Sea and Aleutians we have a large strong low
north of Amchitka Sunday with the front arcing to St Matthew
Island then to the Pribilofs and crossing the Aleutians at the
triple point near False Pass. High end Gales will be in advance of
the front and storm force wind is likely in the southern quadrant
of the low along the Central Aleutians Sunday. The storm barrels
into the mainland Monday followed by weak high pressure across the
Bering Sea. Yet another storm then moves into the picture again
Wednesday likely bringing gale to storm force wind the the
central and western Aleutians along with ample warm advection.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155
MARINE...Gale 119-125 127 130-132 139 150 155 165 170 173-185.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AMD
LONG TERM...SA