Gale Warning 669, NWS Anchorage, AK

878 
FZAK61 PAFC 022358
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
258 PM AKST Sat Dec 2 2017

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.

PKZ399-031430-
258 PM AKST Sat Dec 2 2017
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...
A front in the southwest Gulf moves into the northern Gulf through 
Mon. The associated North Pacific low will move to 54N 159W at 962 mb
by Sun morning then to 56N 156W at 960 mb by Sun afternoon and 
inland by Mon morning. A second North Pacific low will move to 55N 
156W at 997 mb by Mon afternoon.

$$

PKZ351-031430-
Gulf of Alaska Offshore North of 57N and West of 144W-
258 PM AKST Sat Dec 2 2017

...STORM WARNING SUNDAY NIGHT...

.TONIGHT...SE wind 15 to 25 kt. Seas 9 ft.
.SUN...SE wind 30 to 45 kt. Seas 10 to 15 ft building to 17 to 20
ft in the afternoon. Rain.
.SUN NIGHT...S wind 35 to 50 kt. Seas 19 to 33 ft.
.MON...SW wind 30 to 45 kt. Seas 18 to 31 ft.
.MON NIGHT...SE wind 15 to 25 kt. Seas 11 to 18 ft.
.TUE THROUGH WED...SE wind 15 to 25 kt. Seas 9 to 15 ft.
.THU...SE wind 25 kt. Seas 16 to 19 ft.

$$

PKZ352-031430-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
258 PM AKST Sat Dec 2 2017

...STORM WARNING SUNDAY NIGHT...

.TONIGHT...SE wind 15 to 30 kt. Seas 9 to 14 ft.
.SUN...S wind 30 to 45 kt. Seas 13 to 21 ft. Rain.
.SUN NIGHT...SW wind 40 to 55 kt. Seas 20 to 32 ft.
.MON...S wind 25 to 40 kt. Seas 15 to 28 ft.
.MON NIGHT...SE wind 10 to 25 kt. Seas 9 to 17 ft.
.TUE THROUGH WED...SE wind 10 to 25 kt. Seas 8 to 16 ft.
.THU...SE wind 25 kt. Seas 16 to 20 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKST Fri Dec 1 2017

Updated long term discussion

.ANALYSIS AND UPPER LEVELS...
A large gale force low over the northern Bering Sea and its
leading frontal trough approaching the southwest mainland are the
main weather features. Widespread westerly small craft to gale
force winds are evident across much of the Bering Sea and Aleutian
Islands. Southerly gales were also observed in advance of the
front along the Alaska Peninsula and coastal Southwest Alaska. A
mix of rain and snow were observed over the Southwest mainland.
Satellite imagery shows a broad area of open cell cumulus showers
with cold advection on the backside of front across much of the
Bering Sea. Elsewhere, generally fair skies with patchy low
clouds and fog were observed across Cook Inlet and inland
locations across Southcentral with weak gap flows over the North
Gulf Coast and eastern Kenai Peninsula.

&&

.MODEL DISCUSSION...
12z models are in fairly good agreement with the front which
sweeps across the mainland tonight and Saturday. They are starting
to come in better agreement with a second system heading toward
the AK Peninsula on Sunday. The EC which had been on the slow side
had come into better alignment with the 12z GFS which is what we
are leaning toward this forecast package. That said, the 18z NAM
came in with a completely difference scenario with this low
center.

&&

.AVIATION...
PANC...generally will be looking at VFR conditions through the TAF
period with the possibility of a brief bout of MVFR with a little
snow Saturday morning. There will likely be some LLWS Sat followed
by gusty southeast winds across the airport complex Sat afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sat and
Sun)...
The weekend will feature a 1 to 2 punch of active weather. The
first will come from the west and slide through the area on
Saturday. The biggest impact from this will be snow across the
Susitna Valley. A potent jet aloft coupled with a fair amount of
moisture in the column and sustained upslope flow will lead to
steady snowfall throughout the valley. A Winter Weather Advisory
is in effect to address this. As this feature slides further east,
it will produce an increase in south to southeast flow across
much of southern AK. The result will be mixed precipitation for
the Cook Inlet region. While things could start out cold enough
for snow, warmer air and those winds will cause precipitation to
become mixed. This could take a few hours longer in colder,
sheltered valleys, but eventually, the winds will erode the cold
air and bring a mix to just about all locations south of Palmer.
Coastal areas will turn to rain even earlier and will receive a
decent soaking from this first front.

The stronger system is due to arrive Sunday. This system will
bring abundant warm air, moisture, and very strong winds from the
North Pacific. As the system drives towards southwest AK, winds
out of the southeast will increase across southern AK. The
direction will favor the typical southeast gaps such as the
Turnagain Arm, Portage Valley, and the Copper River. Winds could
reach near warning-level (75 mph) in the Turnagain Arm, but it is
still a bit too far out to have enough certainty to include it in
the forecast. A storm-force barrier jet is also expected to form
along the northern Gulf coast. These winds and the warmer air will
work in tandem for places on the lee-side of the mountains to see
the warmest temperatures in quite some time Sunday into Monday.
For many of the population centers, these winds will keep
precipitation at bay. However, across the Susitna Valley, if the
cold air can linger long enough, there could be another round of
heavy wet snow. It should turn over to a mix or all rain by Sun
afternoon though with relentless warm air. Rain could be heavy
along coastal locations with Seward expected to get over 2.5
inches during the event. The other concern with this system is the
rapidly rising freezing levels. This could allow heavy, wet snow
or rain to fall upon old snowpack in the mountains and
significantly decrease snow stability. Back country users should
check the latest local avalanche forecast at alaskasnow.org before
venturing out.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Low pressure over the Bering pushes the front currently along the
Southwest coast, to the Alaska and Aleutians Ranges tonight. Deep
southerly flow off the surface surges a warmer air mass through
the Kuskokwim Valley warming temperatures through the column
enough to bring rain for Bristol Bay and across much of the Lower
Kuskokwim Valley. Snow is expected mainly north of an east to west
line along Sleetmute. However, the front will not bring much
accumulation overnight as it rapidly weakens since it outruns the
associated parent low in the Bering. The next front to watch
moves up to the Alaska Peninsula on Sunday. There is still a bit
of uncertainty on this system and should be monitored for wind
and precipitation changes.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Low pressure across the western Bering fills through the weekend
as the next developing low races north to the Alaska Peninsula on
Sunday. Weak short waves moving about the Bering low keeps
ongoing showers through the short term forecast. Zonal flow along
the base of the low across the west Bering advects a colder air
mass back toward the central waters which brings mixed precipitation
along a modified air mass.

&&

.LONG TERM FORECAST (Monday through Friday)...
Monday the strong storm will have crossed the Alaska Peninsula
and the associated front will have pushed inland along the Gulf of
Alaska coast. This storm will be near Nunivak Island Monday
moving to the Saint Lawrence Island area by Tuesday afternoon. The
latest models have come into better agreement on this solution.
As the front moves in along the coast it will target the southern
mainland with a river of warm moist air. This scenario is
indicative of a strong wind along Turnagain Arm and higher
elevations of the Chugach Monday supporting a chinook setup. With
this comes strong cross barrier flow that will result in the
typical lee side drying and minimal if any precipitation over much
of south central Alaska.

On the backside of this storm will be the strong northwest wind
across the Eastern Aleutians and Alaska Peninsula that will
rapidly turn to the west as the wind slowly diminishes Monday.

As we head into Tuesday the models are struggling with a
consistent solution with respect to bringing another low toward
the Alaska Peninsula. The GFS and ECMWF are roughly 600 nm apart
for the low center. At this point we will continue along with the
WPC solution as confidence is low in the details of the long term
forecast into the middle of next week. There is however good
confidence in a much more active and warmer weather pattern for the
Gulf and South Mainland for early-mid next week with great consensus
in a building ridge over the west coast. This will leave the Gulf
and South Mainland under the influence of deep southerly flow with
the potential for a series of systems to quickly moving north
through the area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory for Snow 145.
MARINE...Gale Warning 175 176 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...SA/DEK