Gale Warning 724, NWS Anchorage, AK

761 
FZAK61 PAFC 210003
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
303 PM AKST Sun Dec 20 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.

PKZ399-211415-
303 PM AKST Sun Dec 20 2020
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...

A 993 mb low near 59N 150W moves inland near 60N 145W at 1001 mb 
Mon morning. A strong front enters the western Gulf Mon 
afternoon and then moves inland along the north Gulf Coast by Tue
afternoon. A 967 mb low forms along the front near 52N 155W Mon
evening and moves to 58N 155W at 958 mb by Tue afternoon.

$$

PKZ351-211415-
Gulf of Alaska Offshore North of 57N and West of 144W-
303 PM AKST Sun Dec 20 2020

...STORM WARNING MONDAY NIGHT...

.TONIGHT...W wind 20 to 30 kt. Seas 10 to 13 ft.
.MON...S wind 20 to 30 kt. Seas 11 ft.
.MON NIGHT...SE wind 25 to 40 kt increasing to 35 to 50 kt after
midnight. Seas 14 to 22 ft. Rain.
.TUE...SE wind 35 to 50 kt. Seas 22 to 29 ft.
.TUE NIGHT...SW wind 20 to 30 kt. Seas 21 to 28 ft.
.WED...S wind 15 to 30 kt. Seas 16 to 24 ft.
.THU THROUGH FRI...N wind up to 15 kt. Seas 11 to 19 ft.

$$

PKZ352-211415-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
303 PM AKST Sun Dec 20 2020

...STORM WARNING MONDAY NIGHT...

.TONIGHT...W wind 20 to 30 kt. Seas 10 to 13 ft.
.MON...S wind 15 to 30 kt increasing to 25 to 40 kt in the
afternoon. Seas 10 to 18 ft.
.MON NIGHT...SE wind 35 to 50 kt. Seas 15 to 28 ft. Rain.
.TUE...S wind 35 to 50 kt. Seas 21 to 28 ft.
.TUE NIGHT...SW wind 20 to 30 kt. Seas 19 to 26 ft.
.WED THROUGH THU...SE wind 15 to 30 kt. Seas 14 to 22 ft.
.FRI...NW wind 15 kt. Seas 10 to 15 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKST Sat Dec 19 2020

.ANALYSIS AND UPPER LEVELS...

In the big picture there is a low in the northern Gulf moving
inland and another one in the eastern Bering Sea with less overall
lift, but some nicely organized snow showers around it and along
the front associated with it. The jet stream is well south of the
forecast area and not giving any upper level support to either
low. As is often the case in Alaska, the details really make or
break the forecast so a closer look at the northern Gulf low
system is in order. The surface low is in the northern Gulf, but
the 500 mb low is over the Kuskokwim Valley with a 500 mb trough
extending to the southeast from the low to lower Cook Inlet as of
early Saturday afternoon. This is creating enhanced lift over the
area with a heavier a band of snow from the northern Kenai Peninsula
to over Anchorage and the west side of Knik Arm. This is not a very
strong system, but these weaker systems are often the ones that
produce the heavier snow events in Anchorage and this is one of
those examples.

&&

.MODEL DISCUSSION...
Model data today is a mixed bag of: good, bad and ugly. The bad
is the way models did not do well with the setup of the snow band
that was over the western Kenai Peninsula and Anchorage bowl
today. They did not start to align (or some even recognize there
would be snow in Kenai or Anchorage) until well into the event.
Hi-res models have now caught up as did the 18Z NAM and GFS.

The ugly is the handling of the complex low tonight into Tuesday
over the Bering Sea. The location of the strong front associated
with this low is handled well so we can have fairly high
confidence as to where this front will impact areas and that is
the good part of the models. It is also good that we know it will
be a strong low with lowest pressure likely dropping under 950
mb. However, the location and strength of the multiple centers is
all over the map across the Bering Sea. Looking at MSLP on all
models put on top of each other shows how different they are and
it is difficult to have confidence in any one location over the
Bering Sea in this situation. This will affect the locations of
Gale and Storm force winds and the timing of them, though most
areas of the Bering will see at least Gales at some point.

&&

.AVIATION...
PANC...IFR snow will continue through the afternoon and then
improve early evening. Visibility is expected to return to VFR
levels after the snow stops, but ceilings may still remain mainly
in or near the MVFR category into tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight through
Monday afternoon)...

The snow event currently ongoing across Anchorage has produced
snowfall amounts ranging anywhere from 4 to 7 inches. As a result
of this a Winter Weather Advisory was issued earlier today for 5
to 8 inches of snow accumulation total for this event. The
advisory is set to expire at 6 pm this evening and this looks to
be on track. Also due to the light and powdery nature of the
snow, high speed vehicular traffic will re-suspend the snow that
is on the ground. The heaviest of the snow is over across
Anchorage with mainly light snow continuing for the next couple
hours. Light snow is expected to begin tapering off later this
evening from west to east before ending around midnight. In
between now and midnight, upwards of an additional inch can be
expected with 1 to 2 inches for the Anchorage Hillside.

Generally, a mostly cloudy sky is expected during the overnight
and into the morning hours Sunday. There may be some isolated
flurries around the area but these are expected to be mostly a
nuisance and for now have been left out of the forecast for the
overnight hours.

The next threat for snow will come quickly again on Sunday.
Another potent upper level shortwave is expected to lift through
the region with the potential for light snow across the
Anchorage Bowl and the Mat-SU Valleys. However, any snow that
falls Sunday will be nothing like today. There may be some light
snow that begins falling around 9-10 am Sunday morning, therefore,
slight chances are in the forecast at this time. The main part of
this event is not expected to start up until the afternoon hours
around 3 PM. Likely PoPs were brought in at this time and continue
through 9 PM Sunday for the time period when the best chance for
any accumulating snowfall to occur. Current thinking is anywhere
from 0.5 to 1 inch across much of Anchorage and the Mat-SU
Valleys. There is the potential for some areas north of Anchorage
to maybe see a bit more than 1 inch but think that will be the
highest most places see. Some light snow is also expected for the
southern Kenai Peninsula including Homer with possibly just a
coating of snowfall. Kenai was just kept in flurries for this
package on Sunday as most of the activity is expected to be east
of them.

Late Sunday night into midweek, the weather pattern becomes even
more active, shifting towards the warmer/windier. A strong Bering
low bringing a similarly strong front and possible atmospheric
river eastwards into Southcentral. Impacts could include the
potential for high winds through Turnagain Arm and the Gulf
waters, Chinook/downsloping into Anchorage and the Mat Valley with
high winds on the Anchorage Hillside, heavy snow through the
coastal mountains causing localized blizzard conditions, heavy
rain along the coast increasing flooding concerns, rising snow
levels, heavy snow along the Alaska Range, increased avalanche
concerns, and treacherous travel conditions in many areas. Stay
tuned for more on all those hazards.

What can be said with high certainty is that stargazers hoping to
catch the conjunction of Jupiter and Saturn Monday evening should
plan not to be anywhere near Southcentral Alaska, as cloud cover
will be widespread here.

&&

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

Bristol Bay and the AKPEN will remain in showery conditions
tonight into early tomorrow morning as the remnants of a weak
surface low pushes onshore and fizzles out. Elsewhere will remain
relatively dry until the front off a storm force low pushes the
Southwest Coast tomorrow night. This is an impressively strong
system bringing significant amounts of precipitation, winds, and
warmer air advection to the Southern AKPEN and the Southwest
Mainland. Heaviest precipitation will be along the AKPEN and in
upslope areas (eastern side of the Kuskokwim Mountains), while
downsloping should keep the leeside drier. Precipitation will be
a rain/snow mix transitioning to rain along the Southern AKPEN
Sunday and Monday. Snow is expected along the higher elevations,
upslope areas (especially Dillingham and Togiak Village), and
areas west of Bethel with accumulations of 2-4 inches possible.
Higher elevations will have higher snow accumulations. Lower
elevation will likely be downsloped out or see light snow showers
with little to no accumulations expected. Strong winds are
expected Sunday night and Monday, with the strongest winds through
the passes along the AKPEN and Bristol Bay, as well as the
leeside of the Kuskokwim Mountains.

&&

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

A complex multi-center low pressure system enters the Western
Bering late tonight. Model spread is large for this system with
respect to low centers, however, there is pretty good agreement
for the leading front. Widespread gales and small craft winds will
dominate the Bering through tomorrow night both along and behind
the front. Storm force winds will follow the front tonight and
tomorrow, by tomorrow night through Monday they will wrap around
the low and take over the Central/Northern Bering. Since models
are not in great agreement for low centers, areas of storms
differed between the models, thus, a broad, widespread approach to
storm force winds was used. While confidence is high for storms,
exact duration and location may vary.

Precipitation along the front will track from west to east along
the Aleutian Chain beginning Sunday morning. This will mostly be
moderate to heavy rain or a rain/snow becoming light after frontal
passage. Snow is likely to remain in the higher elevations with
accumulations of 4-8 inches possible. Additionally, widespread
rain and snow showers are expected across the Bering along and
behind the front.

&&

.Marine (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska
A storm force low will be present in the Gulf on Tuesday, with a
hurricane force barrier jet set up possible along the Southcentral
coast. This low is expected to exit early Wednesday, with
southerly winds remaining. There is moderate confidence in another
low entering the Western Gulf on Thursday. This low looks to move
north from the Pacific and looks to be at least gale force in
strength. Overall, an active weather pattern is in place for the
Gulf of Alaska.

Bering Sea:
A broad area of low pressure is expected to be in place over the
Bering Sea on Tuesday, with gale force winds possible. This low
should weaken and move north out of the Bering Wednesday, with
generally calm conditions present through Thursday. There is at
least moderate confidence in this forecast. A possibility of a
compact low moving right along the Western Aleutians exists on
Thursday, but most weather associated with this low looks to
remain south of the islands. However, there is still uncertainty
with this system so adjustments may be needed.

&&

.Long Term (Days 4 through 7/:Tuesday through Saturday)...

An active weather pattern will continue into the long term. A
storm force low with a hurricane force barrier jet will be present
in the Gulf of Alaska Tuesday. Broad low pressure will be present
in the Bering, also with storm force winds possible. As the week
progresses, another low looks to move north into the Gulf of
Alaska on Thursday. This low looks to be at least gale force in
strength, but its exact track is not determined yet. The Bering
looks to quiet some midweek. A large and powerful low then pulls
into the Western Bering on Saturday. While this low is a ways off,
it preliminarily looks to be storm force in strength.

It should be noted that models continue to have difficulty in the
long term, so confidence in the long term tops out at a moderate
confidence level. We are confidence in the presence of the major
low pressure systems mentioned in the previous paragraph, but
adjustments will need to be made to location and track. Due to
uncertainty, an ensemble approach was used in the long term with a
blend of the GFS and ECMWF, which was collaborated on with WPC.
Therefore, we anticipate leaning on WPC grids, especially with the
low in the Bering late next week. To sum it, active weather
continues with some major low pressure system anticipated for our
forecast area later this week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WSW 101.
MARINE...STORMS 155 165 170-174 175 179 181 185 412-414.
         GALES 119 120 132 138 160 175 177-180 351 411.
FIRE WEATHER...NONE.

&&

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