Gale Warning 602, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 PM AKST Sat Nov 14 2020

.ANALYSIS AND UPPER LEVELS...The pattern is dominated by a
sharply building ridge over the Bering with a broad longwave
trough over the mainland. Within the trough there is widespread
cold air and a weak low in the Northern Gulf of AK. This weak low
provided just enough moisture streaming over top of the cold air
to produce some light snow (around 1 inch) over parts of the
Anchorage Bowl this morning. After the snow, fog once again
settled in the Bowl and over parts of the Matanuska Valley. Over
the Western Aleutians, the signs of the next system are already
evident. Some mid and high clouds are quickly streaming north from
the North Pacific into the Western Aleutians and southerly winds
are already making it into Shemya.

In the upper levels, a potent 300mb jet (around 30,000') is
supporting all of these key features. It currently flows from
west to east at 130 kt into the Western Bering as it supports the
developing North Pacific low. It then makes a sharp turn to the
north up and over the building ridge. It then dives back down at
120 kt through the Eastern Bering and returns to due west-east
flow well south of the Gulf.

&&

.MODEL DISCUSSION...Models remain in good agreement with all of
the main synoptic features. The preferred models with the
incoming system for the Western Aleutians were once again the GFS
and the Canadian as they have been the most consistent with the
strength and track. The main areas where the models continue to
struggle involve any chance for precipitation associated with the
low in the Northern Gulf and fog in Southcentral. Hi-res models
and hand edits were used to handle these features. The shortwave
that moved through the YK Delta last night into this morning was
not resolved well by the models, but it appears this feature is
now quickly falling apart.

&&

.AVIATION...
PANC...Fog is slowly lifting across the Anchorage Bowl. As the
offshore gradient increases and winds start to pick up out of the
northeast, this should allow just enough dry air to mix in to
allow visibilities to continue to improve. However, there is
still plenty of low level moisture to keep some MVFR ceilings into
the late evening. There remains an outside chance that an
inversion could set-up overnight and fog from Knik Arm could once
again move in for Sunday morning. Increasing offshore (NE) winds
Sunday should result in improvement to VFR conditions.

&&

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

A stalled low in the Gulf continues to bring scattered
rain/snow showers to the Prince William Sound area. As relatively
higher pressure builds to the north, stronger northerly winds will
develop. This will push the aforementioned precipitation farther
offshore as well as bring clearing skies and cooler temperatures
to the region. Winds will be strongest though mountain gaps and
passes. The same general pattern will persist through much of the
upcoming week.

&&

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

A cold front has pushed through much of southwest Alaska today, and
snow showers have wrapped up across the Kuskokwim Delta. Clearing
skies tonight will allow for colder low temperatures with teens
and single digits expected. Even chillier conditions are expected
Sunday night as this colder airmass settles in. On Monday, weak
onshore flow develops, and with this flow will come some fairly
widespread fog across the Kuskokwim Delta. On Tuesday, slightly
warmer conditions move in, along with the return of cloud cover.

&&

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

Cold advection will persist across the eastern Bering/Aleutians
tonight through much of Sunday, and this should bring continued
snow showers to the eastern Aleutians through the southern AKPEN
with some light accumulations expected.

Further west, a storm force low will approach the western
Aleutians on Sunday. This storm will continue northeast towards
the Pribilofs late Monday as it gradually weakens below Gale
force. As this storm moves into the central Bering, it will
weaken the cold advection in the Eastern Bering causing the snow
showers to taper off.

Another Gale force front will approach the western Aleutians by
early on Tuesday.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska:

Increasing confidence for a North Pacific low to retrograde into
the Eastern Gulf by Thu. Northwest to north small craft winds and
waves spread back across the Gulf with local Northwest gale force
winds near the Barren Islands and northerly gale force winds over
the Eastern Gulf for Wed and Thu. A new front approaches the
Western Gulf Thu.

Bering Sea:

An Eastern Bering low and front tracks northward through Wed.
Model track and development are mixed but widespread southerly
small craft winds and waves with local gale force winds continue
over the Eastern Bering through Wed. A strong North Pacific low
and front move across the Bering through Thu. Widespread high-end
gale force winds and waves over the Bering with local storm force
winds wrapping the low push eastward through Thu.

&&

.LONG TERM FORECAST (Days 4 through 7)...

The forecast period will commence with a high amplitude ridge in
place over the eastern Bering. Looking west, the models hone in on a
surface low north of Dutch Harbor with a second surface low
southwest of Attu Island. The GFS and the ECMWF are in decent
agreement with the timing and the tracks of the lows. Day 5
(Thursday/Nov 19th) the global models advertise a 3rd low spinning
up south of the central Aleutians with the track staying south of
the chain and moving towards the Gulf Of Alaska. A fourth surface
low will be at the doorstep of Attu and Shemya by Day 7
(Saturday/Nov 21st). Very confident that this pattern will be
progressive and active. Not much of a reprieve from winter in
sight through the end of the forecast period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning: 175-178.
Gale Warning: 130,131,411-413,155,173,174.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BG
MARINE/LONG TERM...MK/PJS