Gale Warning 591, NWS Anchorage, AK

714 
FZAK62 PAFC 061218
OFFALU

Offshore Waters Forecast
National Weather Service Anchorage AK
318 AM AKST Fri Nov 6 2020

Offshore Waters Forecast for the Bering Sea

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.

PKZ499-070200-
318 AM AKST Fri Nov 6 2020
.SYNOPSIS FOR CENTRAL BERING SEA...

A north Pacific low will strengthen to 995 mb and move to 55N 
160W Sat afternoon. Then moves northeast towards Kodiak Island
Sat night. A new 990 mb low approaches 52N 168E Sun morning.

$$

PKZ411-070200-
Bering Sea Offshore West of 180 and East of the International
Dateline-
318 AM AKST Fri Nov 6 2020

.TODAY...SW wind 20 to 30 kt. Seas 14 to 18 ft.
.TONIGHT...SW wind 10 to 20 kt. Seas 12 ft.
.SAT...SW wind 10 to 20 kt. Seas 9 ft.
.SAT NIGHT...SW wind 10 to 25 kt. Seas 6 to 9 ft.
.SUN...S wind 20 to 35 kt. Seas 8 to 13 ft.
.MON THROUGH TUE...SW wind 25 to 40 kt. Seas 14 to 22 ft.

$$

PKZ412-070200-
Bering Sea Offshore 171W to 180 and North of 56N-
318 AM AKST Fri Nov 6 2020

.TODAY...SW wind 20 to 30 kt. Seas 15 to 22 ft.
.TONIGHT...S wind 10 to 20 kt. Seas 10 to 15 ft.
.SAT...SW wind 10 to 20 kt. Seas 10 ft.
.SAT NIGHT...W wind 10 to 20 kt. Seas 7 to 10 ft.
.SUN...S wind 25 to 40 kt. Seas 9 to 14 ft.
.MON...S wind 20 to 35 kt. Seas 14 to 22 ft.
.TUE...SW wind 20 to 35 kt. Seas 22 to 30 ft.

$$

PKZ413-070200-
Bering Sea Offshore 171W to 180 and South of 56N-
318 AM AKST Fri Nov 6 2020

.TODAY...SW wind 15 to 30 kt. Seas 12 to 18 ft.
.TONIGHT...SW wind 10 to 20 kt. Seas 8 to 13 ft.
.SAT...SW wind 10 to 20 kt. Seas 9 ft.
.SAT NIGHT...W wind 10 to 20 kt. Seas 7 ft.
.SUN...S wind 30 to 45 kt. Seas 8 to 16 ft.
.MON...S wind 30 to 45 kt. Seas 16 to 23 ft.
.TUE...SW wind 25 to 40 kt. Seas 19 to 28 ft.

$$

PKZ414-070200-
Bering Sea Offshore East of 171W-
318 AM AKST Fri Nov 6 2020

.TODAY...SW wind 15 to 30 kt. Seas 11 to 18 ft.
.TONIGHT...S wind 10 to 20 kt. Seas 8 to 13 ft.
.SAT...SE wind 10 kt becoming W in the afternoon. Seas 8 ft.
.SAT NIGHT...W wind 10 to 25 kt. Seas 6 to 9 ft.
.SUN...SW wind 20 to 35 kt. Seas 8 to 13 ft.
.MON THROUGH TUE...SW wind 25 to 40 kt. Seas 15 to 23 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
528 AM AKST Thu Nov 5 2020

.ANALYSIS AND UPPER LEVELS...

Satellite shows the much discussed frontal system approaching the
Southwest Coast this morning. Cold air and outflow winds remain
in place over Southcentral, with weak troughing still lingering
along the coast.

In the upper levels, the pattern setting up this weather is shown
as a 500MB closed low located in Eastern Siberia. Troughing from
this low extends into the Bering. This low is part of a long wave
trough encompassing the entire Bering Sea. Another trough is
located over the AlCan border and exiting to our east. This trough
is the remnant of the closed low that was over Southcentral AK
the past few days. A shortwave ridge with an axis over Southwest
AK separates these two areas of troughing.

On the surface, the closed low in the upper levels is reflected as
a large occluded system with a low pressure center of 953mb
located along the coast of Eastern Siberia. The front from this
system is approaching Southwest AK. Strong zonal flow with a tight
pressure gradient is behind this front, along with post-frontal
trough. This indicates strong winds in the forecast should play
out. Over Southcentral, IR satellite indicates cold air is still
in place at the surface. Troughing is still in place along the
coast. Offshore winds can be observed on satellite with streets
of cold core cumulus and areas of glacial dust coming out of the
Copper River Delta and even a bit out of the Susitna.

&&

.MODEL DISCUSSION...

Models are in good agreement to start the short term, handling
major weather features well. Models have been on track with the
large weather system in the Bering for a couple days now, so we
have high forecast confidence there. The same goes for cold air
and offshore winds in Southcentral AK. Model disagreement emerges
for the next system coming in this weekend. The GFS would like to
take the next low through the Western Gulf, while the ECMWF takes
a track bringing the low through Bristol Bay and into Southwest
AK. This is a significant difference in low track and will result
in very different weather depending on which model is correct.
Right now we are leaning GFS as it has been consistent with its
track the past few days while the EC has flip-flopped on its
track. However, with such a disparity between two majors models,
forecast confidence decreases over the weekend. Details of this
next system are in the long term discussion.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist for most of the
day. This evening, a weather system will move into Southcentral
AK. This will bring light snow and MVFR conditions for both
ceilings and visibility through the night. Snow will clear in the
early morning hours allowing visibility to improve, but MVFR cloud
cover will remain through the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today
through Friday Night)...

The one hazard product still out this morning is the High Wind
Warning for Thompson Pass. While there haven't been any hurricane
force gusts recently, the winds have been fluctuating and gusts
have occasionally approached 65 mph. Thus, will allow the Warning
to continue for the next few hours. Either way, the approaching
front already throwing high cloudiness across the Cook Inlet
region is turning the large scale flow southerly. This will cause
the winds to rapidly diminish through the day today, and that
looks to be the end of the bitterly cold strong gap winds for the
foreseeable future in Southcentral. In fact, the front is
transporting a much warmer, more seasonable air mass into the
area. However, it will not do so uneventfully. As the front sweeps
eastward this evening into tonight, it will bring enough moisture
into the area to cause light snow to break out all across the Cook
Inlet region by 9pm.

There are a few points of note with this front. First, the front
will be weakening and shearing apart as it moves east, thus, the
further east you go the less snow can be expected. Second, the
front is running into a very dry atmosphere currently in place
across Southcentral. Thus, a component that may delay the start
time of the snow and also cut into snowfall totals is the time it
will take for the snow to saturate the atmosphere. Third, unlike
past events (and likely upcoming ones), there will not be any
concern about precipitation type with this one. The air mass is
plenty cold enough for all snow in all areas, even along the
coast. Fourth, this is a fast moving front, with the snow moving
through and done over a span of 6-12 hours, with the longest snow
where upslope persists longest. Thus, the primary forecast
challenge will be how much snow will be seen. Since it's an
eastward moving front that will be crossing several mountain
ranges, think the westerly flow pushing the front along will favor
the highest snow amounts along Hillside and higher elevation
areas, as that flow allows for upslope enhancement. Think west
Anchorage, the western Kenai Peninsula, and the Mat Valley from
Wasilla west will get anywhere from 1 to 3 inches of accumulation.
The Hillside, Palmer and the eastern Mat Valley, and higher
elevations will see higher totals, in the 2 to 5 inch range. With
0.9 inches of snow for the winter to date, a 2 inch snowfall in
west Anchorage would triple the winter cumulative total from
where it is now.

By sunrise Friday morning, most areas except any persistent
mountain snow showers should be done with the significant snow
across the Cook Inlet region, with only snow showers expected
across the Copper River Basin and Prince William Sound. Most areas
will see a mix of sun and clouds for the day. Zonal flow
associated with a building upper level ridge over the area will
keep all of Southcentral quiet weather-wise through Friday night.
The next low will encroach on Kodiak Island Saturday morning. This
low has the potential to be a very impactful event for
Southcentral, including strong winds, rain for some areas, and
significant snow (more than 6 inches) for others. There is still
considerable uncertainty with who will see what impacts, so stay
tuned.

&&

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

The forecast remains on track with a weakening occluded front
approaching the Southwest coast today. A brief period of snow
showers may precede the front but will quickly transition to rain
as southwesterly flow brings in warmer air. Thus, temperatures
will increase quite a bit over the next couple days. Snow is
expected further inland across parts of the Kuskokwim Valley and
higher elevations through tonight, with accumulations of less than
~3 in. By Friday, precipitation should be confined to the higher
elevations, with elsewhere seeing some drier conditions through
Friday night as the front dissipates. A second system out of the
North Pacific may bring some rain and strong winds to the AKPEN
and Bristol Bay on Saturday. Models are struggling some with the
track of this low and will need to be monitored over the next
couple days.

Coastal flooding continues to be a concern Thursday into Friday
for Kuskokwim bay to Hooper Bay. Guidance has consistently shown
surges ~3-5 ft above Highest Astronomical Tide (grassline) over
the last couple days, allowing a Coastal Flood Warning to be
issued.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A weakening storm force front pushes east across the Bering this
morning. Widespread gales and areas of storm force winds will
persist through tonight as the front pushes onshore. Additionally,
widespread light rain showers are expected for much of the area
through Friday. Warm air advection behind this front will keep the
chance for warning level wind gusts to a minimum. A second system
approaches the AKEPN by Saturday, bringing active weather for the
Central/Eastern Aleutians, including rain and strong winds.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska: Latest guidance continues to show the Saturday to
Monday timeframe being very active across the Western Gulf. A
gale force storm system is expected to begin impacting the area
Saturday morning with winds increasing from southwest to northeast
throughout the day. Gale force winds are expected through Monday
before slowly diminishing below gale force Monday morning/afternoon.
There also may be a brief period of storm force winds through the
Barren Islands into the Western Gulf Sunday afternoon/evening but
this is less certain. The exact track and strength of the low
will determine if the winds reach storm force from the Barren
Island into the Western Gulf.

Bering Sea: Saturday is expected to be the beginning of another
active period for the Bering Sea with a gale force storm system
beginning to impact the region Saturday morning. This initial low
continues moving towards the Pribilofs Saturday evening with
another low on its heels. Beyond Saturday night, the details of
what exactly happens and how this low develops/moves diverge
among the model guidance. Either way model guidance shows another
storm force storm system moving into the Bering Sea.

&&

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

The long term forecast period continues to look active for much of
Southern Alaska including the Bering Sea and Aleutians. For the
Bering Sea and Aleutian Chain, a parade of storm systems is
expected to keep the area unsettled for the duration of the this
time frame. A low is expected to move from the southwest corner of
the Bering northward towards Saint Lawrence Island sometime
Tuesday afternoon. This will yield to a great push of warm air
across the Bering and into Southwest Alaska leading to precipitation
type issues. With this push of warm air, depending on how much
cold air is able to hold on at the surface, a mix of snow, sleet,
and freezing rain and even plain rain is possible. Accompanying
the unsettled weather will be an increase in winds across much of
the Bering Sea, Aleutians, and Southwest Alaska. Storm force winds
are possible through the Aleutian Chain and into the Bering Sea.

Farther east, models continue to remain in disagreement on the
exact track of a low moving northward from south of the Aleutians.
One model (GFS) brings the low northward and develops a triple
point low to the east of the Kenai Peninsula Sunday morning that
then continues into Prince William Sound. The other models (ECMWF,
Canadian-NH) keep one low center that moves northward straight
into Bristol Bay with no triple point low development. If this low
were to take a further west track with no new triple point
development just east of the Kenai Peninsula, then much warmer air
will be able move into Southcentral. This will cause
precipitation type issues. This solution appears unlikely.
However, with the triple point low development which seems more
likely, this could mean an increased chance for snow across the
Southcentral area as cold air will be able to hold on as this low
would pull cold air south into it and the low would be east of the
area placing Southcentral on the northwest side. After this storm
moves out of the region Sunday night into early Monday, a brief
upper level ridge will build across Southcentral that may provide
a respite from the active weather the day prior. This break will
be short-lived though as southwesterly flow in the upper levels
moves back across Southcentral and starts up another period of
active weather for late Tuesday through early Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 131.
         COASTAL FLOOD WARNING 155.
MARINE...STORMS: 170, 172-174, 176, 185, 411, 412, 414.
         GALES: 132, 150, 155, 160, 165, 171, 175, 177-181, 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MV