Gale Warning 740, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKST Tue Dec 29 2020

.ANALYSIS AND UPPER LEVELS...

A vertically stacked 964 mb low has moved into the far western
Bering. Despite it weakening, it is still leading to widespread
rain/snow showers west of the Pribilofs and over the
central/western Aleutians. Strong southerly flow between the upper
level Bering low and a ridge over western Canada combined with a
weak surface low is currently bringing more widespread rain/snow
to the eastern Aleutians. Much of Southwest Alaska remains dry,
although some of the aforementioned precipitation is expected
along the Bristol Bay and Kuskokwim Delta coasts. Farther east, a
front is moving along the Gulf coast. Rain (and higher elevation
snow) will persist across western Prince William Sound and the
western/southern Kenai Peninsula. Given the cross-barrier flow,
Anchorage and the Mat-Su are expected to remain mostly cloudy, but
precipitation-free this morning.

&&

.MODEL DISCUSSION...

Synoptic model agreement remains good. Confidence remains high
for a very strong low (with central pressures possibly as deep as
925 mb) moving over the western Aleutians on Thursday into
Friday, leading to hurricane force winds and 40-50 ft seas.
Conditions will be much more benign over Southcentral in the
coming days. Precipitation will be confined to the Gulf coast
through today. Models indicate a potent shortwave moving over
Anchorage on Wednesday morning. Although some models do not show
associated QPF, given the intensity of this shortwave combined
with weak surface flow, it would not be out of the question to see
a quick 1-2 inches of accumulation. Temperatures will be cold
enough in the mid 20s. Weak offshore flow looks to develop towards
the end of the week, bringing in a cooler and drier pattern.

&&

.AVIATION...

PANC...There is a chance of patchy fog developing around Cook
Inlet this morning, which could lead to periods of LIFR
conditions. Otherwise light winds and clear skies will persist
into Wednesday morning. Light snow is possible thereafter,
potentially reducing visibilities and lowering ceilings to MVFR.

&&

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

The inland areas of Southcentral is in a break between systems
this morning with partly cloudy to clear skies over the region.
The next system is moving into the Kodiak area early this morning
and will weaken as it moves northward. An upper level wave
associated with this low will also move northward through both
Cook Inlet and Prince William Sound tonight which will bring in
precipitation to these areas. Most of this precipitation will be
snow except for the farther south areas such as Homer and Cordova
where there may be a rain-snow mix. The timing of this wave brings
the best snow chance for Anchorage between 3 AM and 9 AM
Wednesday morning.

&&

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

A storm over the North Pacific will lift northward across the
Alaska Peninsula late tonight, then weaken as it continues
northwestward across the eastern Bering Sea on Tuesday. This
will bring gusty winds and areas of light precipitation to the
Southwest Alaska coast. With a warm air mass in place, and
additional warming likely as the storm passes by, expect rain or
a mix of rain/snow in the Bristol Bay/Alaska Peninsula region and
snow or a mix of rain/snow along the Kuskokwim Delta coast. In
the wake of this surface low, an upper level short-wave trough
will lift northward across the region Tuesday night through
Wednesday. This will bring a better chance of precipitation,
especially to Bristol Bay. A slight cooling of the airmass will
lead to a transition back toward mostly snow. High pressure will
then build overhead Wednesday night and Thursday, leading to dry
conditions and cooler temperatures.

&&

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

A vertically stacked low over will continue to spin over the
central to western Bering Sea through Wednesday, with a series
of short-waves rotating around the center. This will maintain a
showery pattern with locally gusty winds. Attention will then
shift to a major storm developing over the northwest Pacific.
While there remains some uncertainty in the exact track of this
low, the forecast is on track to bring widespread storm force
winds to the Aleutians and central Bering Sea Wednesday night
through Thursday, with a smaller area of Hurricane Force winds
likely on the south side of the low center. There could be a
period of snow and blowing snow when precipitation first arrives
Wednesday evening, especially for Shemya, but expect winds and
warm air advection to warm up surface temperatures fairly quickly.
A high wind warning may eventually be needed for somewhere along
the central to western Aleutians, but that will depend heavily on
the track of the low center.

&&

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

Gulf of Alaska:
Confidence is increasing with a deeper low moving into the Gulf on
Tuesday, which now looks to bring another round of Gale force
winds along the North Gulf Coast. Afterwards conditions throughout
the Gulf will fall to Small Craft or below starting on Wednesday,
before the next Gale force front skirts the Southern Gulf starting late
Thursday.

Aleutians/Bering:
Model agreement and forecast confidence remains very good on the
track of an extremely deep low moving into the Western
Aleutians/Bering late Wednesday into Friday. Confidence is
greatest that this system will bring Storm to potentially
Hurricane Force winds to most areas west of Dutch Harbor. This
system will also bring high seas to the region, which could reach
as high as 40-50 ft along the Pacific coast west of Adak. This
system looks to be the deepest low to move through the region
since the remnants of Typhoon Nuri in 2014, which nearly set the
North Pacific record for minimum central pressure.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...
The remnants of the extremely deep, to potentially record
breaking Western Aleutian low will dominate the long term forecast
beginning on Friday. This may allow for a few weeks lows to move
through the Gulf into this weekend, however at this point they
look to be centered far enough to the south to keep any
significant impacts away from the South Mainland. In general
though, model agreement and forecast confidence is below average
by late this week, largely due to significant uncertainty with
the remnants of the Bering low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...DEK