Storm Warning 206, NWS Anchorage, AK

202 
FZAK62 PAFC 310042
OFFALU

Offshore Waters Forecast
National Weather Service Anchorage AK
342 PM AKST Wed Dec 30 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.

PKZ499-311330-
342 PM AKST Wed Dec 30 2020
.SYNOPSIS FOR CENTRAL BERING SEA...

A 947 mb low at 46N 165E will strengthen as it moves to 54N 174E 
at 925 mb on Thu afternoon, with the highest wave heights and 
winds between Shemya and Adak, and continues to 55N 175E and 
weakens to 936 mb on Fri afternoon.

$$

PKZ411-311330-
Bering Sea Offshore West of 180 and East of the International
Dateline-
342 PM AKST Wed Dec 30 2020

...HURRICANE FORCE WIND WARNING THURSDAY...

.TONIGHT...S wind 20 to 35 kt becoming SE 45 to 60 kt after
midnight. Seas 14 to 22 ft. Snow.
.THU...E wind 50 to 65 kt. Seas 16 to 31 ft building to 25 to 35
ft in the afternoon. Snow and rain.
.THU NIGHT...SE wind 40 to 55 kt. Seas 25 to 40 ft. Snow and rain.
.FRI...SE wind 30 to 45 kt. Seas 21 to 35 ft.
.FRI NIGHT...SE wind 25 to 40 kt. Seas 17 to 31 ft.
.SAT THROUGH MON...N wind 25 to 40 kt. Seas 16 to 24 ft.

$$

PKZ412-311330-
Bering Sea Offshore 171W to 180 and North of 56N-
342 PM AKST Wed Dec 30 2020

...STORM WARNING THURSDAY AND THURSDAY NIGHT...

.TONIGHT...S wind 15 to 25 kt increasing to 20 to 35 kt after
midnight. Seas 8 to 12 ft.
.THU...SE wind 45 to 60 kt. Seas 10 to 18 ft building to 14 to 29
ft in the afternoon. Snow.
.THU NIGHT...SE wind 35 to 50 kt diminishing to 25 to 40 kt after
midnight. Seas 21 to 33 ft. Snow.
.FRI...S wind 15 to 30 kt. Seas 22 to 31 ft.
.FRI NIGHT...SE wind 20 to 35 kt. Seas 18 to 25 ft.
.SAT...E wind 20 to 35 kt. Seas 16 to 25 ft.
.SUN THROUGH MON...N wind 15 to 30 kt. Seas 11 to 15 ft.

$$

PKZ413-311330-
Bering Sea Offshore 171W to 180 and South of 56N-
342 PM AKST Wed Dec 30 2020

...HURRICANE FORCE WIND WARNING THURSDAY...

.TONIGHT...S wind 10 to 25 kt becoming SE 40 to 55 kt after
midnight. Seas 8 to 16 ft. Snow.
.THU...SE wind 50 to 65 kt. Seas 16 to 30 ft. Snow and rain.
.THU NIGHT...S wind 35 to 50 kt. Seas 22 to 37 ft. Snow.
.FRI...S wind 25 to 40 kt. Seas 21 to 34 ft.
.FRI NIGHT...S wind 20 to 35 kt. Seas 19 to 32 ft.
.SAT...S wind 20 to 35 kt. Seas 16 to 31 ft.
.SUN...E wind 10 to 25 kt. Seas 9 to 14 ft.
.MON...N wind 15 to 30 kt. Seas 10 to 15 ft.

$$

PKZ414-311330-
Bering Sea Offshore East of 171W-
342 PM AKST Wed Dec 30 2020

...STORM WARNING THURSDAY...

.TONIGHT...SW wind up to 15 kt becoming E after midnight. Seas 5
to 8 ft.
.THU...SE wind 20 to 35 kt increasing to 35 to 50 kt in the
afternoon. Seas 5 to 8 ft building to 9 to 14 ft in the afternoon.
Rain.
.THU NIGHT...SE wind 30 to 45 kt. Seas 11 to 19 ft. Rain and snow.
.FRI...S wind 15 to 30 kt. Seas 13 to 21 ft.
.FRI NIGHT...S wind up to 20 kt. Seas 11 to 18 ft.
.SAT...SE wind up to 20 kt. Seas 12 to 20 ft.
.SUN THROUGH MON...N wind 10 to 25 kt. Seas 7 to 12 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
543 PM AKST Tue Dec 29 2020

.ANALYSIS AND UPPER LEVELS...

Deep southerly flow between a nearly stationary trough centered
over the Western Bering and a ridge of high pressure over the
Interior/Yukon Territory continues to bring widespread cloudcover
and scattered rain/snow showers to the Southwest mainland. Just to
the east of this cloud cover, subsidence with the high pressure
allowed for a clear and cold morning today, along with some patchy
fog around Upper Cook Inlet.

A shortwave trough within the southerly flow over Kodiak Island
brought rain to the area today. This feature will continue
progressing northward this evening, and will be the focus for
light snow for much of Southcentral overnight. A weak low under
this shortwave trough is beginning the cross over the AKPen where
it is bringing rain and wet snow to the area as it progresses
northward. The western Bering low continues to slowly weaken and
drift westward. Winds from this system have now fallen below gale
force, but otherwise is not producing significant impacts outside
continued scattered shower activity.

&&

.MODEL DISCUSSION...

In general, synoptic model agreement remains good through
Wednesday leading to above average forecast confidence for much of
the area. There are some very minor timing differences with how
quickly the shortwave over Kodiak Island will move northward into
Southcentral early Wednesday morning that is producing some
uncertainty in the onset/dissipation of any snowfall, but
confidence is good in the forecast trends over the next 2 days.
Model agreement also remains very good with the extremely deep
low that will move into the Bering by Thursday. There still
remains around 10 mb in spread in this systems extremely low
central pressure between the most aggressive EC and least
aggressive NAM. The forecast continues to favor the GFS as a
middle ground solution. As far as impacts from this system
however, there is very good agreement in the location and timing for
highest winds and seas into Friday.

&&

.AVIATION...

PANC...VFR conditions with light/variable winds will continue
until overnight tonight, when a few hours of IFR snow and around
1 inch of accumulation is expected. As is mentioned in the model
discussion above there is some uncertainty in exact timing of
this feature, but there is generally good confidence that VFR
conditions will redevelop again after 18z on Wednesday.

&&

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

In the next two days, a mix of rain and snow will move across
much of Southcentral and Kodiak Island. A frontal boundary over
the northern Gulf will drive heavier rainfall inland this evening
before transitioning to snow along Prince William Sound and
Anchorage Bowl northward tonight. Meanwhile, warm temperatures
over southern Kenai Peninsula and Kodiak Island will maintain
precipitation in the form of liquid throughout most of the
forecast period.

A stacked low over Shelikof Strait will bring another round of
snowfall across the Bowl and Southcentral by Wednesday and
Wednesday night. GFS and NAM struggles a bit on the placement of
the upper low, with the GFS aiming to keep the upper low over
Anchorage Bowl and delay its motion eastward in the next couple
days. NAM whips the upper low past Anchorage Bowl by Thursday
morning and parks it over Prince William Sound through Thursday
night. Should the upper level low linger over the Anchorage Bowl
or PWS, new updates to the forecast will be provided. For now, the
amount of snowfall would likely be more over the Anchorage Bowl
than other areas tonight.

Much colder temperatures aloft will linger between the Susitna
Valley and Copper River Basin before spreading eastward toward
Valdez and Thompson Pass on Thursday. At 850 mb, environmental
temperatures upstream will continue to fall to -16 degrees
Celsius by Thursday night. The potential for patchy freezing fog
around Port Valdez and Thompson Pass is feasible starting
Wednesday night through Thursday night. Light winds near Valdez
northward and along the southern Cook Inlet and lower temperatures
in the next couple nights will invite freezing fog in those
areas. As a result, it'll be relatively quiet and a bit cooler in
the next couple days.

&&

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

An upper level short-wave trough and surface low along the Alaska
Peninsula will lift northward across the Bristol Bay region
tonight through Thursday, bringing periods of light precipitation.
The airmass is warm enough to produce mostly rain this afternoon
and evening, but expect a transition to mostly snow overnight.
Snow accumulation will be light, with an inch or two at most by
Thursday afternoon. The remainder of Southwest Alaska will be on
the fringes of this system, with patchy light precipitation.

A ridge of high pressure will build overhead Wednesday night
through Thursday, leading to dry conditions, cooler temperatures,
and most likely areas of fog. For Thursday night through Friday,
a strong front associated with a hurricane-force low along the
western Aleutians will near the Southwest Alaska coast. It looks
like ridging over the mainland will hold the front at bay, so most
areas will likely remain dry. However, expect an increase in
easterly winds, especially along the immediate coastline.

&&

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

A large low spinning over the western Bering Sea will continue to
produce showers and gusty winds across much of the region through
Wednesday. Attention will then shift to what could end up being a
record-breaking storm. A weak low near Japan will rapidly
intensify ahead of short-wave trough moving out of Asia, aided by
a 200 kt+ upper level jet and extreme thermal gradients
between a sub-tropical air mass over the Pacific (850 mb
temperatures of +12 degrees Celsius or warmer) and a polar
airmass over Asia (-20 degrees Celsius near the coast). This low
will bottom out as it reaches the western Aleutian Islands
Thursday morning. Models continue to trend deeper with the central
pressure, with the various solutions ranging from 919 mb to 930
mb. This will rival the Bering Sea storm from November 2014 which
developed from the remnants of Typhoon Nuri. The estimated
central pressure of that storm was 924 mb. In any case, the
combination of extremely low pressure and rapidly falling pressure
as the storm arrives will lead to widespread storm force to
hurricane force winds along the Aleutians and into the Bering Sea
Wednesday night through Thursday. The low will stall along or
north of the western Aleutians, which means the most extreme
weather will remain in that area. The frontal system will progress
eastward across the Bering Sea and Aleutians Thursday through
Friday, weakening as it progresses eastward. Winds will remain
elevated along the Aleutians the entire time, as arctic air feeds
into the back side of the storm.

Have issued a High Wind Warning from Adak to Atka for the leading
front with southeasterly winds. At the moment it appears the
strongest core of winds on the south side of the low center
Thursday will remain away from populated islands. This could
change if the low track shifts, so stay tuned to the latest
forecasts.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska:
Confidence remains high for a broad low center to gradually drift
northwards over the southern Gulf on Friday with gale force winds
likely north of the low, or near the northern Gulf Coast. Winds
should decrease to small craft levels as the low and associated
front weaken from late Friday to early Saturday. Forecast
confidence decreases from Saturday to Sunday as the aforementioned
low slowly drifts towards the Gulf Coast and continues to weaken.

Several smaller lows may rotate around the broader circulation
this weekend and potentially track across the southern Gulf with
locally small craft to gale force winds possible as they push
eastwards. However, confidence for these individual low tracks is
poor at this time. This uncertainly stems from the placement of
the Gulf low by the weekend and from differences in the evolution
of the extremely deep low spanning across the Bering during the
forecast period.

Aleutians/Bering:
Forecast remains on track for an extremely deep to potentially
record setting low to track across the Western Aleutians and into
the western Bering Thursday into Friday. By Thursday evening, the
center will be positioned north of Attu with widespread storm
force winds wrapping the low to the west of Adak and across much
of the Bering, with an area of hurricane force winds likely
between Attu and Adak across the Rat Islands. Southeast gale to
storm force winds are also expected ahead of the low's front as it
tracks through the Central Bering/Aleutians and Pribilofs on
Friday. Waves as high as 40-55 ft will be possible on Friday near
the Pacific coastline of the far Western Aleutians until winds
weaken below storm force early Saturday. By Saturday, there is
good confidence the low will stall in the far western bering as it
slowly fills with winds weakening to gale force on Saturday, then
dropping to mostly small crafts from late Saturday to Sunday.
Winds along the front will quickly diminish as the boundary also
stalls in the eastern Bering on Saturday morning.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through
Tuesday)...

Despite continuing to have the remnants of a potentially record
setting low in the Bering, the weather for much of the southern
mainland for Saturday look quite benign with high pressure
dominating most areas. There is good agreement in low pressure in
the extreme southern Gulf through Saturday, that will produce
outflow winds to the typical channeled areas of the Gulf Coast,
however this does not look to impact most interior locations.
Starting Sunday, this Gulf low pressure will begin to lift into
the north Gulf Coast, likely bringing with it warming conditions
and a chance of precipitation to the Gulf Coast/Southcentral. By
Monday, model agreement becomes very poor, so forecast confidence
for early next week is very low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 185.
MARINE...Hurricane Force Wind Warning: 177 178.
Storm Warning: 175 176 411 413.
Gale Warning: 119 130 185 412.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
MARINE/LONG TERM...AS/DEK