Small Craft Advisory 868, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKST Fri Nov 13 2020

.ANALYSIS AND UPPER LEVELS...
A broad upper trough aloft extends westward from the Gulf of
Alaska to over the East-Central Bering Sea. At the surface, low
pressure continues over the the Gulf with a south moving low near
the Kuskokwim Delta. Showers...mostly rain showers, are over the
Gulf and Bering Sea/Aleutians/AK Pen, with rain and snow showers
over the Kuskokwim Delta. Low stratus and fog that developed over
the Anchorage Bowl with the passage of yesterday's system
continued into the afternoon hours today. Low stratus also
developed over the Copper River Basin this morning and held on
into the afternoon hours. Gusty outflow winds continued over the
Eastern Kenai Peninsula with with fairly brisk westerly flow
across the Western Gulf. Satellite imagery showed a fairly broad
area of open cell cumulus across the Aleutians/Western Bering Sea
associated with cold advection.

&&

.MODEL DISCUSSION(short term)...
Southcentral...Models are in generally good agreement with the
synoptic features. The main issues will be gap/outflow winds which
will be generally handled best by the high res models.

Out West...Models are in relatively good agreement on the storm
force flow heading toward the Western Aleutians Saturday night
into Sunday. Models differ after that into Monday with the NAM
being the main outlier.

&&

.AVIATION...
PANC...IFR/LIFR conditions in fog during the overnight and morning
hours expected once again. Some improvement likely in the
afternoon Saturday. Light winds will prevail.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

Light winds and saturation at low levels will continue to bring
fog in the Anchorage area overnight into early Saturday morning.
This will also keep temperatures steady near 30. A broad low
stalled in the Gulf is bringing isolated to scattered rain/snow
showers along the coast through western Prince William Sound.
These will gradually end Saturday as relatively higher pressure
builds to the north and pushes the showers farther offshore.
Northerly flow will increase through the weekend and persist into
early next week. Gusty winds are likely in terrain gaps as well as
the city of Valdez. However, they are likely to remain non-
impactful given the lack of upper level forcing. Elsewhere,
clearing skies and cooler temperatures are expected.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Saturday
through Monday)...

An upper level trough that has been stuck over the region for the
past couple of days will move southward tonight as an arctic front
pushes in. This will bring an end to the snow showers across the
Kuskokwim Delta and usher in a considerably colder airmass and
offshore flow for late Saturday through Sunday. For Sunday night
into Monday, a ridge of high pressure will build into Southwest
Alaska. As it does so, weak onshore flow develops along with
warmer air moving in aloft. This will create a favorable setup for
fog on Monday across much the Kuskokwim Delta.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Saturday morning through Monday)...

On Saturday, an upper ridge will build across the western Bering,
with an arctic front quickly pushing southward through the
eastern Bering/Aleutians by mid-morning. Behind this front, cold
advection will set the stage for widespread snow showers across
the Bering and the Eastern Aleutians/AKPEN. Some light
accumulations are expected.

On Sunday, a Gale force low will approach the Western Aleutians
bringing widespread rainfall. Northerly flow/cold advection will
weaken across the eastern Aleutians/AKPEN causing the snow showers
to taper off.

For Monday, a ridge of high pressure moves into the Eastern
Bering as the Western Aleutians storm system lifts towards the
Pribilofs while gradually weakening. Expect gale force wind gusts
across the central Bering/Aleutians early, but decreasing below
Gales late day as the storm weakens.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska:

Small craft winds are expected across the Gulf Monday. There is
increasing confidence that a low over the southeastern Gulf
retrogrades to the northwest, bringing the potential for northerly
gale force winds across the central Gulf Tuesday night into
Wednesday. By Wednesday night, a gale force front approaches the
Gulf from the west.

Bering Sea:

A storm force low enters the western Bering Monday and lifts into
the northern Bering by Monday night. Southerly gales and storm
force winds can be expected over the western and central Bering
waters. There is increasing confidence that a second storm force
low enters the western Bering Tuesday afternoon and phases with
the first. This results in a broad complex low bringing gales and
storm force winds to the Bering waters through Wednesday.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through
Friday)...

A large, amplified upper level ridge in place over the eastern
Bering will extend over the western mainland Tuesday afternoon.
Farther west, a strong upper level low and its associated surface
low will push a front eastward across the Bering, bringing warm
southerly flow and rain to the Aleutian Chain Tuesday into
Wednesday. A broad complex low will be in place across the Bering
Sea by Wednesday morning with an ample supply of cold air filling
in on the backside. Upper level shortwaves embedded within this
low will eject eastward across the southern mainland beginning
Wednesday night. Model solutions continue to struggle with the
timing and track of several of these features, however the bottom
line is that an active weather pattern is likely to persist across
southern Alaska through Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 172,174,178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BG
MARINE/LONG TERM...KO