Small Craft Advisory 970, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
511 PM AKST Mon Dec 16 2019

.ANALYSIS AND UPPER LEVELS...
An upper low over the northwestern Gulf Alaska continues broad
cyclonic flow over the Gulf and the southern and western mainland.
At the surface, a weakening occluded front stretches east to west
from the eastern Gulf coast to over Bristol Bay. Rain or
rain/snow mix was evident along this boundary over the Gulf and
eastern Kenai Peninsula with light snow from western Cook Inlet/SW
Susitna Valley to over Bristol Bay. General easterly flow in the
low to mid levels continued downslope drying to the lee of the
Kenai and Chugach Mountains.

Further west, an upper long wave made headway east to over the
Aleutians. At the surface, a 980s mb low was evident near the
central aleutians with an occluded front stretching east to near
Unalaska. Rain and southerly gales were evident east of the
surface low. To the west, snow mixed with rain and near storm
force northerly winds were observed.

&&

.MODEL DISCUSSION...
Models are synoptically in good agreement through the short-term
forecast period. Overall, will be performing relatively minor
edits.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Active weather mainly impacts the Gulf and surrounding coasts
through mid week with drier cooler conditions inland. Patchy fog
is expected to develop across the Copper River Valley late tonight
as low level moisture increases and a steep temperature inversion
persists. Fog will likely persist through Wednesday as the pattern
remains stagnant across the interior during this time. Across the
Gulf, a weak front brings additional rain and snow to the
northern waters and coast tonight...followed by a more organized
system, which develops just south of Kodiak Island Wednesday
morning. Rain is expected with the fronts over the Gulf with a mix
of rain along the immediate coasts. Cooling temperatures aloft,
Tuesday afternoon into Wednesday, will likely change precipitation
over to snow for coastal and inland locations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A front will approach the Alaska Peninsula (AKPEN) tonight,
stalling just south of it as cyclogenesis (low pressure
development) commences south of the region in the north Pacific.
This low that develops on the southern end of the front lifts
north towards Kodiak Island on Tuesday, stalling southwest of the
island, before moving off to the southeast late Tuesday night.
This helps to maintain northeasterly winds across the southwest
mainland, helping to advect colder air from central portions of
the state into the region. This flow pattern will allow any
precipitation to be confined to the AKPEN/Bristol Bay region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
An area of low pressure near Amchitka will slowly weaken as it
slides southeast, before becoming absorbed into a developing North
Pacific low that heads towards Kodiak Island. This allows colder
air to drop southward across the region, helping increase the
ocean Delta Ts (temperature difference between the waters surface
and 850 mb/~4400 feet), allowing some shallow instability to
develop. Given the weak instability and cold advection, expect a
showery type precipitation pattern to become more widespread, with
snow showers becoming the more prominent type across most areas.

&&

.MARINE (Days 3 through 5)...

New guidance is giving higher confidence in the likelihood for
gale force outflow winds in the northwest Gulf around Kodiak
Island Thursday into Friday. A strong North Pacific low is being
suggested by most models for entering the Western Aleutians
Saturday. However, uncertainty exists in the low's track. Guidance
agrees on an eastward path, but deviations in the northward
extent will play a strong role in where the strongest winds are.
Right now, most models agree that gale force winds can be expected
with a couple of outliers suggesting storm force or small craft
level winds.

&&

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

The extended period starts off quiet and cold for southern
mainland Alaska, as an upper level low allows for more winter like
temperatures to return through the weekend. A more active period
will ensue Saturday with a storm system that will bring more
active weather to the Aleutians and progress into mainland Alaska
to start the work week. Warm Pacific air will likely intrude on
the colder air in place and precipitation can be expected for
Bristol Bay and much of southcentral Alaska on Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 130 175>178.
 Heavy Freezing Spray 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...LTB