Gale Warning 706, NWS Anchorage, AK

460 
FZAK61 PAFC 011315
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
415 AM AKST Tue Dec 1 2020

Offshore waters forecast for the Gulf of Alaska West of 144W

Wind forecasts reflect the predominant speed and direction
expected. Sea forecasts represent an average of the highest
one-third of the combined wind wave and swell height.

PKZ399-020200-
415 AM AKST Tue Dec 1 2020
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...

A front in the central Gulf remains nearly stationary through Tue
night. The associated 969 mb low at 55N 156W moves north and
inland at 980 mb Tue night. Weak low pressure remains in the
northern Gulf through Wed night.

$$

PKZ351-020200-
Gulf of Alaska Offshore North of 57N and West of 144W-
415 AM AKST Tue Dec 1 2020

.TODAY...S wind 20 to 30 kt. Seas 18 ft.
.TONIGHT...S wind 20 to 30 kt. Seas 16 to 19 ft.
.WED...SW wind 10 to 25 kt. Seas 12 to 17 ft.
.WED NIGHT...W wind up to 20 kt. Seas 11 to 15 ft.
.THU...NW wind up to 15 kt. Seas 8 to 13 ft.
.FRI THROUGH SAT...E wind up to 20 kt. Seas 7 to 12 ft.

$$

PKZ352-020200-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
415 AM AKST Tue Dec 1 2020

.TODAY...S wind 20 to 30 kt. Seas 19 ft.
.TONIGHT...SW wind 15 to 30 kt. Seas 14 to 20 ft.
.WED...W wind 10 to 20 kt. Seas 12 to 18 ft.
.WED NIGHT...W wind 20 kt. Seas 10 to 16 ft.
.THU...NW wind up to 15 kt. Seas 8 to 13 ft.
.FRI...E wind up to 20 kt. Seas 6 to 9 ft.
.SAT...E wind up to 20 kt. Seas 8 to 16 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 AM AKST Mon Nov 30 2020

.ANALYSIS AND UPPER LEVELS...

A weakening storm force low positioned south of Dutch Harbor, in
the left exit region of an impressive 170 kt jet, continues to be
the dominant weather feature across the forecast area this
morning. Temperatures overnight have cooled enough for many areas
along the Aleutian Chain to transition from rain to snow with
gusty winds as the front progresses eastward. Quieter conditions
are set up over Southcentral Alaska, with a few lingering snow
showers across the region associated with an exiting upper level
shortwave. In Anchorage, the main concern this morning is fog
that has set up overnight.

&&

.MODEL DISCUSSION...

Models continue to do well with the overall synoptic features
through the short term. However, they are still struggling with
some of the smaller features, including whether the Turnagain Arm
winds will make it into Anchorage on Tuesday or not. There is also
some uncertainty in whether to increase precipitation across
Southcentral on the backside of the low when colder air comes in
on Wednesday. Good model agreement continues over the western
domain, resulting in high-res models being used to capture winds
across the AKPEN.

&&

.AVIATION...

PANC...Fog will remain in the vicinity through the next few hours,
with conditions improving to VFR late morning. A chance for show
returns late afternoon into the evening, with lower visibility and
ceilings expected.  Wind shear will develop this afternoon and
increase through the evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Wednesday Night)...

A very active weather pattern will impact Southcentral over the
next several days. Widely scattered snow shower activity ongoing
along the Gulf Coast near Cordova and in the western Susitna
Valley will continue through the day, but will be increasingly
enhanced by the incoming storm system through the afternoon.

A strong front is approaching the southern end of Kodiak Island
this morning. After sunrise, the front will move north past
Kodiak. Precipitation will begin as snow, but will mix with and
then change over to rain this afternoon. Behind the front, a
strong southerly flow of Pacific moisture will keep rain showers
going off-and-on through Tuesday across Kodiak Island.

The front will continue tracking north this afternoon, reaching
the north Gulf coast this evening. The front will cause heavy rain
along the coast and precipitation will start as snow inland.
Meanwhile, the front will also cause winds to increase with gusts
to 60 mph along Turnagain Arm and higher elevations this evening.
Gusts to hurricane force are expected with the barrier jet south
of Cordova this afternoon and evening as well.

The front will move north into the mountains then drive inland
across all of Southcentral tonight. Behind the front, an
unseasonably warm air mass is being drawn northward into
Southcentral with a tap to the tropics. As this warm air moves
north, the snow will change over to rain from south to north and
over most lower elevation locations as temperatures warm well into
the 30s, and into the 40s in a few areas through Tuesday. In the
Seward area, as much as 5 inches of precipitation, most of which
falling as rain, will cause flooding concerns through Wednesday.
Elsewhere, rain falling on frozen ground, specifically Tuesday
morning when temperatures in many areas first rise above freezing,
will lead to very slick travel conditions across Southcentral. The
warm air and abundant moisture will also increase avalanche
potential in many of the area mountains as well, as heavy, wet
snow falls on the existing snowpack.

Meanwhile, the steady moisture-rich south to southeasterly flow
will also lead to significant snowfall across portions of the
Susitna Valley through Wednesday. Cool, below freezing air will
persist longest in these areas. For the northern Susitna Valley,
this will be because the warm air will be far away from its
source, and the cold air will persist longest before being eroded.
For the western Susitna Valley, plentiful upslope cooling will
"artificially" keep temperatures cooler, prolonging the snowfall
over the area. Thus, a Winter Storm Warning is in effect for up to
3 feet of new snow through Wednesday afternoon.

This pattern will be persistent for at least 24 hours because the
parent low driving the warmth into Southcentral will be nearly
stationary near the Alaska Peninsula through the day on Tuesday.
On Wednesday, the cold air wrapping around the west side of the
low will finally begin to move the upper level trough supporting
the low eastward. The cold air will follow a typical pattern,
being stuck on the west side of the Alaska/Aleutian Ranges through
Tuesday, but will get through the gaps and around the southern end
of those ranges on Wednesday. At some point during the day, with
the exact timing still uncertain, the cold air will advance
northward behind the low into Cook Inlet and eventually to the
rest of Southcentral. As the cold air arrives, a brief period of
snow is expected for Anchorage and the Valley, most likely
Wednesday afternoon. This of course will also be associated with
falling temperatures dropping well below freezing Wednesday night.
The snow shower activity will take its time ending Wednesday
night, especially along the coast, as the flow will remain
southerly. Thus, it will remain an upslope flow, supporting the
continued snow shower activity.

&&

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

A cold and fairly active weather pattern is expected for Southwest
Alaska over the next 3 days as a storm system moves northeastward
along the AKPEN from this afternoon through Tuesday afternoon.
This storm system will bring snow and strong winds to the
Kuskokwim Valley and Bristol Bay. The heaviest snow will reach
Bristol Bay this afternoon and evening. The heaviest snow for the
Kuskokwim Valley will occur late this afternoon through Tuesday
afternoon. Total snow accumulations of 6-11" are expected across
Bristol Bay and 5-8" across the Kuskokwim Valley. Strong winds
will blow this snow around and reduce visibility. The biggest
visibility reductions are expected to be across the central
Bristol Bay area, where visibility could be reduced to a half a
mile at times. This blowing snow is expected to reach the
Kuskokwim Delta, though the snow will not be as heavy there so
visibility reductions will not be as much as in Bristol Bay. Winds
will generally remain too light for significant blowing snow
across the Kuskokwim Valley. Winter Weather Advisories have been
issued for both the Kuskokwim Valley and Bristol Bay for snow and
for Bristol Bay blowing snow in addition to snow. Temperatures
will become much colder in the wake of this storm system as brisk
northeasterly off shore flow will bring in continental polar air
from the Alaskan interior.

&&

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

The weather pattern will gradually become more benign over the
next 3 days across the Bering/Aleutians as the current storm
system south of the Aleutians moves northeastward into the Gulf of
Alaska. Gale force winds will continue across the central and
eastern Bering/Aleutians today and tonight then decrease to below
gale force on Tuesday with the exception of the gaps along the
AKPEN. The main concern for Tuesday and Wednesday is ocean effect
snow across the western AKPEN and the eastern Aleutians as strong
cold air advection is expected over the warmer waters of the
Bering. This pattern will make for unstable lapse rates across the
eastern Bering and initiate convective snowbands that will move
over the western AKPEN and eastern Aleutians.

&&

.MARINE (Days 3 through 5)...

The period commences with the last vestiges of a decaying low
over the Northern Gulf of AK while a new low moves from the North
Pacific towards the Aleutians. First in the Gulf, winds will
finally subside below gale-force as we head through the day Wed
into Thu. The rest of the week will feature primarily cold air
advection westerly flow with a strong low east of our area over SE
Alaska.

Bering...The pattern will continue to feature rapid and dynamic
cyclogenesis. On Wednesday, broad northerly flow over the Eastern
Bering will yield to a new system developing south of Dutch Harbor
Wed night into Thu. There is high confidence in at least gale-
force winds with this low, however, storm-force winds cannot be
ruled out. This low will lift north into the Central Bering by
late Thu. A new low will then take its place on Fri. There is
solid model agreement and moderate confidence in the pattern until
the Fri system. At that point, it looks like at least gales will
once again be possible, but the exact strength and location by Fri
night is quite uncertain.

&&

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

Going into the second half of this week, guidance indicates a
pattern shift is ahead. Aloft, strong southerly flow pushes off
to the east and exits Southcentral AK. In Southwest AK and the
Bering/Aleutians, there are indications that shortwave ridging
will move in behind the exit of the longwave trough. Moving into
the weekend, model guidance shows this ridging moves over
Southcentral and phases with a longwave high pressure ridge
extending up the West Coast from high pressure in the Western US.
Low pressure then returns the the Western Bering.

On the surface, high pressure exists over Mainland AK while a
series of lows moves north through the Eastern Gulf of Alaska and
into the Southcentral Coast, keeping trough along the coast. Low
pressure also exists in the Bering. It should be noted that there
is considerable spread in the models both aloft in the general
pattern and at the surface with specific features. Especially with
specific low pressure systems, there is too much disagreement to
be able to discern what will happen in the long term. When it
comes to the pattern, there is disagreement in what will happen,
but guidance is at least indicating the pattern setup mentioned in
the previous paragraph. Therefore, we can have some confidence in
a pattern shift ahead, but there is too much uncertainty to
identify specific features.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 145.
         Winter Weather Advisory 152 161.
         Flood Advisory 125.
MARINE...Heavy Freezing Spray 160 180 181.
         Storm Warning 119 120 131 132 351 352.
         Gale Warning 125 128 130 136-141 150
                      155 160 165 170-176 179-181 413 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
SOUTHCENTRAL ALASKA...JPW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...BB