Small Craft Advisory 116, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
332 PM AKST Mon Feb 5 2018

.ANALYSIS AND UPPER LEVELS...
A surface low near the western Alaska Peninsula and its associated
weather front to the north and east are spreading moisture into
Bristol Bay and the western Gulf. There is a fairly distinct
boundary frontal boundary with above freezing temps(generally
rain) over Bristol Bay and below freezing temps with pressure
driven drainage flows inland. The King Salmon NEXRAD shows
precipitation spreading north across Bristol Bay. East to
northeast winds are also increasing ahead of the advancing
low/front across Bristol Bay and Southwest Alaska. Rain has spread
to Kodiak Island with the front and clouds are streaming north
across the Gulf and The Southcentral Mainland. Strong outflow
winds are still occurring in a few places across the northern
Gulf, particularly Thompson Pass/Keystone Canyon, Valdez Narrows,
and the Copper River Delta.

&&

.MODEL DISCUSSION...
Models are in fairly good agreement and reasonable through
Wednesday across Southcentral. Significant model differences arise
with the low complex over the western and central Bering
Sea/Aleutians Tuesday night and Wednesday. Confidence is fairly
low on exact placement of lows, however the swath of gales over
the eastern Aleutians/eastern Bering are fairly consistent
regardless of model solution.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through this
evening. MVFR to IFR conditions are expected with snow beginning
early Tuesday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A shift in the pattern is ongoing as a warm front lifts into the
North Gulf Coast. Clouds streaming out ahead of the front have
already infiltrated Southcentral. As the front closes off into a
low, it will slow down and stall south of Prince William Sound.
Light snow will spread inland with the highest values along the
Kenai Peninsula, diminishing as the front moves northward.
Anchorage may see an inch of snow or so, with slightly higher
amounts on the Hillside. Snow will be very fluffy and low density,
so some blowing snow behind vehicles may be an issue for the
morning commute. The low will weaken and drift east Tuesday with
weak offshore flow helping to dry the region back out although
flurries/light snow showers will be possible through Tuesday
before clearing out Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A front draped across the southwest mainland will continue to
move north this evening as the associated upper level
trough/surface low tracks north through the eastern Bering. Warmer
air behind the front will push north and override cold air
trapped at the surface leading to isentropic lift and a wide area
of precipitation over much of the mainland. Warmer air will erode
the cold surface air for locations on the AKPEN and on the leeward
side of the Aleutian Range, leading to rain mixing in with snow
for King Salmon and Iliamna. Further west along the Bristol Bay
coast, cold northerly flow at the surface will persist through
most of the night keeping precipitation all snow for places like
Dillingham and inland areas north and west of Dillingham.
Therefore, 6-8 inches of snow is expected near the coast while up
to 10-12" can be expected further inland north and west of
Dillingham by tomorrow morning. Moderate snow combined with strong
winds will lead to areas of blowing snow and visibilities as low
as 1/2 mi tonight. Therefore, the Winter Weather Advisory remains
on track through early tomorrow morning.

The front will elongate and weaken as it continues north and west
into the Kuskokwim Valley and Kuskokwim Delta tonight, so
generally expect lighter snow accumulation. The front will stall
in the Kuskokwim Valley which may lead to a longer period of light
snow. Blowing snow can also be expected along the Kuskokwim
Delta, though visibilities are not expected to fall as much as in
Bristol Bay due to the lighter nature of the falling snow. A few
showers will linger through Tuesday, though generally expect
conditions to dry out. Precipitation will taper off by Tuesday
afternoon as the low continues tracking north out of the area and
a ridge of high pressure builds in by Wednesday, leading to
overall drier conditions.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A surface low will continue to track north of the Eastern
Aleutians tonight bringing an end to rain and snow showers. As
the associated front lifts away from the island chain, an area of
snow showers will pass through the Pribilofs. By Tuesday
afternoon, the pattern becomes a bit more amplified as an upper
level trough digs south across the western Aleutians inducing a
ridge over the eastern Aleutians. A strong southerly jet will
develop ahead of the trough and move north across the central
Aleutians bringing gale force winds, warm temperatures, and a
steady stream of rain, resembling an atmospheric river. The steady
stream of moisture will slowly shift east from Adak to Dutch
Harbor through the day on Wednesday and eventually to the eastern
Aleutians/AKPEN by Wednesday night.

&&

.LONG TERM FORECAST (Wednesday evening through Monday night)...
We will be returning to a weak outflow pattern, clear skies and
lighter winds, except for gaps of the north gulf coast where
gustier winds can be expected in favored areas. From there, the
pattern amplifies through the weekend as a front moves into the
Gulf of Alaska through the Aleutians. Guidance is in better
agreement today with the setup of the progressive pattern. It
looks active, a series of fronts will traverse the area through
next week. The jet stream stays mostly south of our area, only
briefly impinging up on the mainland, so a big warm-up is not in
the cards at this point. On the flip side, because of the storm
track and cold air in place, it appears as if the fronts will be
numerous but just clipping Southcentral each time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 161.
MARINE...Gale Warning 120 130 131 138 170 172>174 180.
 Heavy Freezing Spray 127.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...ML