Small Craft Advisory 1006, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKST Fri Dec 25 2020

.ANALYSIS AND UPPER LEVELS...

The unsettled weather continues across much of Alaska. A broad
upper trough extends from the Western Bering Sea to the Northeast
Pacific. At the surface, there is a low south of Attu Island, a
low near the Pribilof Islands, a low near the AKPEN and a low
south of Cordova. The low near the AKPEN supports a mature/occluded
system and is producing a broad swath of precipitation from Bethel
to the Barren Islands and Kodiak. A well defined upper shortwave
continues to sustain a low complex over the Central
Aleutians/Central Bering Sea. On the latest ASCAT (Advanced
Scatterometer) gale force winds have been detected near the
Barren Islands, south of Kodiak, south of Atka and near the
Pribilof Island.

&&

.MODEL DISCUSSION...
In the short term period, the models look decent with the
placement of the major synoptic features from the Bering to the
Gulf Of Alaska. Model consensus deteriorates later Saturday and
Sunday. This divergence in model solutions is very noticeable
over the North Pacific.

&&

.AVIATION...
PANC...The expectation is that VFR conditions will persist
this TAF package. Northerly winds will be increasing today.
The main concern today will be the potential for LLWS. The radar
at Kenai actually detected wind shear just after midnight and the
models are pinging into it also.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
A quiet weather pattern is expected for Southcentral AK,
especially for inland areas. The exception will be Kodiak and the
Southern Kenai Peninsula, as a low pressure currently moving into
the Western Gulf will provide precipitation and windy conditions.
Gale force winds can be expected from this system, with highest
winds in gaps and passes. Another low is anticipated to move into
the Northeastern Gulf on Saturday, following the coastline up from
the panhandle. This low still has a lot of uncertainty associated
with it, so more to come on this low as the weekend approaches.
Right now it looks gale force at most and is confined to the coast.

The only significant weather for the rest of mainland AK is that a
high presure setup over Interior Southcentral and low pressure in
the Gulf will cause off-shore winds to blow down the Cook Inlet
and through other gaps around Valdez and the Copper River Delta.
The Mat Valley wind is also expected to pick up. These winds will
be aided by cooler temperatures in the Copper River Basin.
Otherwise, expect quiet weather and pleasant temperatures the next
few days for your holiday festivities.

&&

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

A trough extending over the Kuskokwim Delta from a low in Bristol
Bay will continue to produce areas of light snow and blowing snow
across coastal Southwest Alaska through this evening. The best
chances for measurable snow and reduced visibility from blowing
snow will occur from Bethel west. For King Salmon and Iliamna,
enough warmer air is in place to allow for rain to fall this
morning. However, these rain showers will switch back to snow
showers as colder air works in as the low lifts slowly north this
afternoon.

Light snow showers are expected to linger from interior Bristol
Bay to the Middle Kuskokwim Valley through Saturday as the
aforementioned low drifts north and east in advance of a ridge
that will build over Southwest through the day Saturday.

The next frontal system advances toward the southwest coast late
Saturday, with mixed rain/snow changing quickly to all rain over
the AKPEN. Strong southerly winds will also accompany the front,
ushering in warmer air with temperatures climbing into the lower
40s for Sunday. Elsewhere, the front moves to the Southwest coast
by Sunday morning with snow developing by early Sunday morning.
Snow will again change to rain quickly from Cape Newenham to
Coastal Bristol Bay and Iliamna. Farther north, colder air in
place over the Kuskokwim Delta will allow snow to persist longer.
Gusty winds will also allow for widespread blowing snow through
late Sunday before warmer air finally works in, with snow changing
over to a wintry mix. The front weakens by Monday with
precipitation transitioning to a mix of rain and snow showers as
it tracks east.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A low over Bristol Bay today will continue to produce areas of
snow showers across the eastern Bering south across the AKPEN
through late this evening. A complex low west of Saint Paul is
producing a small area of storm-force winds over the central
Bering along with snow showers as far south as the central
Aleutians. These winds and showers will diminish by Saturday
morning as the low moves to the Pribilofs and weakens.

The bigger story, though, will be a strong, storm-force low moving
from the North Pacific to the southern Bering Saturday. This storm
will deepen to a sub 940mb low as it crosses the Rat Islands. As
it does, it will first push a warm front with easterly storm-
force winds across the western Aleutians late Friday followed
quickly by an occluded front Saturday morning. Widespread
precipitation will accompany the front, with a band of snow
initially quickly changing to rain. Wind gusts may approach
hurricane-force for Attu and Shemya by Saturday morning with the
core of strongest gusts lifting over the western Bering through
the day Saturday. Westerly hurricane-force gusts are also
possible along the western and central Aleutians by Sunday
morning as colder air wraps back underneath the low as it enters
the Bering. Winds along the associated occluded front are
expected to maintain storm-force criteria as it moves over Dutch
Harbor and the Pribilofs Saturday, Cold Bay and Sand Point late
Saturday, and along the Southwest coast by Sunday morning. Any
snow that falls out ahead of the front initially will change
quickly to rain as temperatures jump into the upper 30s to lower
40s.

&&

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

Gulf of Alaska: A strong front from the Bering Sea will track
across the western Gulf waters on Sunday. There was uncertainty
in confidence yesterday, but this now looks like solid gale force
winds with this front. Forecast confidence then drops for Monday
and Tuesday as a series of low rotate up from the Pacific. Will
likely see continued periods of at least gale force winds with
these storms.

Bering Sea: Starting Sunday, a large well established low will be
anchored over the southern Bering Sea, with widespread gale to
storm force winds across Bering, Aleutians, and Southwest coastal
waters. Expect a series of lows to track around this low center
Monday through Tuesday, but forecast confidence in the track and
strength of individual storms is low. Bottom line, gale to storm
force winds will remain a threat through at least Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7: Monday through Thursday)...
Forecast confidence is low to medium at this time with models all
over the place. A complex area of low pressure over the western
Bering on Monday morning looks to remain nearly stationary through
Tuesday before heading east towards the southwest coast on
Wednesday afternoon. This will bring increased winds and
precipitation to the area through Thursday. A North Pacific low
looks to approach the Alaska Peninsula late Thursday, with a
secondary low positioned in the central Bering. Anticipate active
weather associated with all of these systems. A front in the
western Gulf moves towards the northern Gulf coast by Tuesday,
bringing an increase to winds and precipitation to coastal
locations and higher elevations as an area of low pressure forms
along this front. It looks to move inland late Tuesday into
Wednesday. After this, a front associated with a low heading
towards the AKPEN from the North Pacific will enter the western
Gulf late Thursday, bringing another chance for active weather
including winds and precipitation to Kodiak Island and the western
Kenai Peninsula.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch 131 Thompson Pass.
MARINE...Heavy Freezing Spray 181. Storm 170 172 173 174 175 176
178 411 412 413 119. Gale 155 165 171 177 179 185 125 130 131 138
414.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BJB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...MK/CK