Gale Warning 714, NWS Anchorage, AK

099 
FZAK61 PAFC 110023
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
323 PM AKST Thu Dec 10 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.

PKZ399-111430-
323 PM AKST Thu Dec 10 2020
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...
Weakening low pressure remains over the Gulf through Fri morning 
before dissipating.

$$

PKZ351-111430-
Gulf of Alaska Offshore North of 57N and West of 144W-
323 PM AKST Thu Dec 10 2020

.TONIGHT...NE wind 10 to 15 kt. Seas 7 to 11 ft.
.FRI...E wind up to 15 kt increasing to 15 to 25 kt in the afternoon.
Seas 5 to 8 ft.
.FRI NIGHT...E wind 15 to 25 kt. Seas 7 to 12 ft.
.SAT...E wind 20 to 30 kt. Seas 10 to 14 ft.
.SAT NIGHT...E wind 25 to 35 kt. Seas 14 to 22 ft.
.SUN...E wind 15 to 30 kt. Seas 14 to 22 ft.
.MON...E wind 15 to 25 kt. Seas 11 to 16 ft.
.TUE...SE wind 20 kt. Seas 7 to 10 ft.

$$

PKZ352-111430-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
323 PM AKST Thu Dec 10 2020

.TONIGHT...NE wind 10 to 25 kt. Seas 6 to 11 ft.
.FRI...E wind 15 to 30 kt. Seas 7 to 12 ft.
.FRI NIGHT...E wind 20 to 30 kt becoming SE 10 to 25 kt after
midnight. Seas 9 to 17 ft.
.SAT...E wind 25 to 40 kt. Seas 12 to 19 ft.
.SAT NIGHT...E wind 25 to 40 kt. Seas 15 to 25 ft.
.SUN...E wind 15 to 30 kt. Seas 16 to 24 ft.
.MON...SE wind up to 20 kt. Seas 11 to 15 ft.
.TUE...NW wind 15 to 25 kt. Seas 7 to 10 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
715 PM AKST Wed Dec 9 2020

.ANALYSIS AND UPPER LEVELS...

The upper level pattern and jet stream are highly amplified, with
a trough digging from the western Bering well southward into the
North Pacific, a downstream ridge building across the eastern
Bering/Aleutians, and a series of short-wave troughs extending
from western Alaska southeastward into the Gulf of Alaska.

A large deep vertically stacked low just south of the far western
Aleutians is drifting northward. A frontal system out ahead of
this low is tracking north and east across the Aleutians and
southern Bering Sea, producing storm force winds and seas of
20 to 30 ft. Multiple distinct surface waves are noted in
satellite imagery moving along the fronts. Winds are likely
locally stronger in the vicinity of these surface waves.

Meanwhile, what had been a closed upper low over Bristol Bay has
opened into a trough and is tracking east-northeastward across
the western Gulf. This trough is acting upon a cold and unstable
atmosphere, resulting in showers across the Gulf and into
Southcentral. Locally heavy snow is falling from Seward to Moose
Pass, with deep southerly flow bringing bands of snow northward
up Resurrection Bay. A weaker short-wave trough extends northward
across Southwest Alaska, producing some light snow on the west
side of the Alaska and Aleutian Ranges. Lastly, a stronger short-
wave trough extends from the southern Gulf down into the North
Pacific, with a storm force low lifting northward into the
eastern Gulf.

&&

.MODEL DISCUSSION...

Over the past couple model cycles there had been a shift in
handling of the multiple short-waves over Southwest Alaska/the
Gulf. Prior to this, models had been phasing all of the troughs
prior to crossing Southcentral. They still show phasing, but it
occurs later and the trough over the western Gulf takes more of
an eastward track instead of lifting northward across the Kenai
Peninsula. As a result, the portion of the trough which heads up
Cook Inlet to Anchorage and the Mat-Su looks quite weak and will
have to back off of the snowfall forecast for these areas.

With the presence of surface waves along the Bering/Aleutians
frontal system, models have all trended a bit stronger with winds.
Observations across the region are bearing out these stronger
winds. The real challenge is determining whether any of these
waves develop into a closed low. The GFS is more aggressive with
this idea and introduces the possibility of localized areas of
hurricane force winds.

While solutions are fairly close initially with large scale
features, model spread begins to grow on Friday. In particular,
models are struggling with a new trough/deep low lifting north
out of the Pacific and toward the Alaska Peninsula Thursday night
through Friday. There has been an overall westward trend in the
low track, but there is a fairly large spread in the exact track
and depth of the low. Tend to favor the GFS/ECMWF for now because
they represent a middle of the road solution on track and were
closest to inherited forecast.

&&

.AVIATION...
PANC...Tonight's trough passage is looking less and less
impressive. Thus, it looks much less favorable for snow and
associated reduced ceiling/vis. However, in this convective
environment, there could still be a few showers which briefly
move overhead of the terminal. As the trough exits Thursday
morning a strong ridge will build in behind it. With weak low
level flow, expect low level moisture will hand around. Thus,
have indicated ceilings lowering to MVFR. A lack of precipitation
should keep ceilings from going any lower than that. If anything,
it is possible the ceiling could settle at VFR.

&&

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

An upper level trough over the Alaska Peninsula will move across
Southcentral tonight through tomorrow morning. Precipitation will
largely remain over the northern Gulf Coast, with snowfall being
the dominant precipitation type due to cold temperatures aloft
through this time. It previously seemed as though this snowfall
would move across Anchorage, however, the majority of the energy
associated with this upper level trough is now digging further
south than previously anticipated. This will keep inland areas dry
through tomorrow. Following this, high pressure aloft will move
over the area, continuing the dry pattern. Offshore winds look to
remain fairly weak for the north Gulf and eastern Kenai Peninsula.
Low stratus is expected, and possibly fog, to develop along the
Turnagain Arm and into the Anchorage Bowl tomorrow night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3:
Wednesday afternoon through Saturday)...

An upper level trough is moving north across Southwest Alaska producing
light snow west of the Alaska Range. This snow will taper off by
Thursday morning as the trough lifts north of the area. Only minor
accumulations expected north of Iliamna and east of Sleetmute.
No fog expected Thursday and Friday due to clouds and offshore
flow. Temperatures will be cold through Thursday as northerly flow
and cold air advection continues. Friday and Saturday warm air
advection will occur ahead of a frontal system stalling over the
northern and eastern Bering. This front will bring in clouds and
increasing easterly winds, however most precipitation will remain
near coastal locations. Low pressure will approach the AKPEN
however model uncertainty on the strength and track of the low.
The models track the low somewhere near the southern part of the
AKPEN sometime on Saturday and then into the eastern Bering. This
will bring at least gale force winds and rain and snow to the
AKPEN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Wednesday afternoon through Saturday)...

A storm force low and occluded front with hurricane force wind
gusts at times will track across the southern Bering tonight
bringing moderate to heavy rain or a rain/snow mix with
temperatures in the mid to upper 30s. This front will track into
the eastern Aleutians, through the central Bering Sea on Thursday
with rain and snow but no significant snow accumulations
expected. For the Pribilofs, precipitation will begin as snow
through Thursday morning, then gradually mix with and change over
to rain Thursday afternoon and evening. While it is still snow,
the combination of heavier snowfall rates and sustained winds of
35 to 55 mph with gusts to 70 mph will significantly reduce
visibilities. Thus, a Winter Weather Advisory for blowing snow has
been issued from 5am to 6pm Thursday. This front will cause storm
force winds and gusts near or above hurricane force. On Friday
this occluded front will stall along the northern Bering with
winds decreasing to gales by Friday afternoon and continuing to
weaken towards Saturday. Another low will approach the Eastern
Aleutians Friday and Saturday with at least gale force winds and
rain and snow. There is still a lot of uncertainty with the track
and strength of this low, stay tuned.

&&

Marine (Days 3 through 5/Sat through Mon)...

Bering/Aleutians:
Forecast confidence is low for Saturday through Sunday, with
guidance showing large discrepancies in the placement and
intensity of synoptic scale features. In particular, expect a low
to track up from the Pacific and approach the Alaska Peninsula
friday, but unsure of how quickly this low will lift northward
into the Bering Sea. Bottom line, expect widespread gales across
this region at some point during these two days, with potential
for a small area of storm force winds south of the Alaska
Peninsula. Confidence diminishes even further on Monday, so it's
hard to say where storms will be positioned at that point in time.

Gulf of Alaska:

There are discrepancies in the placement and intensity of synoptic
scale features, however most guidance agrees on a deeper low
tracking from the northeast Pacific into the eastern Gulf. Thus,
winds will likely remain below gale force across the western Gulf
waters.

&&

.LONG TERM FORECAST (Days 4 through 7/Sun through Wed)...

The pattern is expected to become more amplified during the day
4-7 period. This trend is reflected in both the GFS and ECMWF
deterministic models as well as their ensembles, however there
are some differences on where these trough and ridge axes are
placed and oriented between both the GFS and ECMWF. A few areas of
consistency in the long range include a ridge axis over the Gulf
of Alaska on Sunday. There are differences on the orientation of
this ridge axis, however, lighter winds and clearer skies are
possible across the northern Gulf. Another area of agreement is
that the ridge axis extends over Southwest Alaska Sunday night
which could result in clearer skies and colder temperatures for
the Kuskokwim Delta and Kuskokwim Valley. GFS and ECMWF ensembles
show signs of a rex block developing over the Bering Sea on
Sunday and persisting into Wednesday as easterly 200 mb zonal
winds in the polar jet region will help weaken the polar jet and
allow for the potential block to form. Ensembles have the upper
trough associated with this rex block over the Bering, thus a
more unsettled weather pattern is expected. Monday through
Wednesday there are many discrepancies at both the surface and the
upper levels which results in a lower confidence forecast.
However, one feature that seems consistent to point out on
Wednesday is the upper level ridge that extends northwestward from
the North Pacific into Bristol Bay.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Winter Advisory: 195.
MARINE...Storm Warning: 170 172-176 179 185 411-414.
Gale Warning: 130 131 150 155 165 171 177 180 181 352.
Heavy Freezing Spray Warning: 130 160 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...CK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...ED