Gale Warning 561, NWS Anchorage, AK

325 
FZAK61 PAFC 042348
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
348 PM AKDT Sat Nov 4 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.

PKZ399-051230-
348 PM AKDT Sat Nov 4 2017
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...
A 1016 mb low near 52N 162W will move to 55N 145W at 988 mb Sun
evening and then to 53N 142W at 980 mb Mon afternoon.

$$

PKZ351-051230-
Gulf of Alaska Offshore North of 57N and West of 144W-
348 PM AKDT Sat Nov 4 2017

...GALE WARNING SUNDAY NIGHT...

.TONIGHT...S wind 15 kt. Seas 3 ft.
.SUN...S wind 15 kt becoming SE in the afternoon. Seas 4 ft. Rain.
.SUN NIGHT...NE wind 30 to 45 kt. Seas 4 to 9 ft building to 9 to
17 ft after midnight. Rain.
.MON...NE wind 35 to 50 kt. Seas 13 to 20 ft.
.MON NIGHT...NE wind 20 to 35 kt. Seas 12 to 19 ft.
.TUE THROUGH THU...NW wind 10 to 25 kt. Seas 6 to 11 ft.

$$

PKZ352-051230-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
348 PM AKDT Sat Nov 4 2017

...STORM WARNING SUNDAY NIGHT...

.TONIGHT...S wind 15 kt. Seas 3 ft. Rain.
.SUN...S wind up to 20 kt becoming N 20 to 35 kt in the afternoon.
Seas 3 to 8 ft. Rain.
.SUN NIGHT...N wind 35 to 50 kt. Seas 7 to 12 ft building to 12 to 
18 ft after midnight. Rain.
.MON...N wind 35 to 50 kt. Seas 15 to 23 ft.
.MON NIGHT...N wind 30 to 45 kt. Seas 14 to 26 ft.
.TUE...N wind 15 to 30 kt. Seas 9 to 17 ft.
.WED THROUGH THU...NW wind 10 to 25 kt. Seas 6 to 11 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Fri Nov 3 2017

.ANALYSIS AND UPPER LEVELS...
The upper level ridge remains over the Gulf of Alaska and into
the mainland part of the state causing widespread subsidence
inversions. A large upper level low is centered northwest of
Kamchatka with a sharp trough extending over the western Bering
Sea and southeastward across Attu Island into the Pacific. This is
the trough that will propagate eastward over the next two days and
impact the weather over the region.

At the surface there is a low in the northeastern Gulf of Alaska
which will move southeast and rapidly exit the Gulf tonight. This
low is causing the tight pressure gradient along the north Gulf
coast. This gradient will also rapidly ease overnight and the low
moves out of the area.

&&

.MODEL DISCUSSION...
The main model issues for the system moving though Southcentral
Alaska and into the Gulf Saturday night into Sunday mostly
resolved on the 12Z runs. The GFS is slowing down the speed of
the upper level trough slightly which brings it into good
alignment with the ECMWF and through the Anchorage and Mat-SU
areas a little slower. The GFS also is slower in causing a cut off
low in the upper level trough which increases the likelihood for
snow in Southcentral as this was a feature that could cut off the
snow chances if it developed too quickly. Models are also now
quickly consolidating the energy into a single low in the Gulf by
late Sunday instead of having a two-low solution.

&&

.AVIATION...
PANC...Fog, and/or low stratus, will continue to be the big
challenge through Saturday morning. While it looks like most of
the dense fog (under a mile visibility) should be done, there may
still be periods of limited visibility. In addition, the fog may
be able to remain a low stratus deck overnight keeping visibility
at VFR or MVFR levels, but IFR ceilings. With a slightly better
mixed atmosphere today and tonight, the stratus persisting seems
the most likely situation.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The synoptic pattern features a ridge axis over the AK Peninsula
with broad northerly flow over Southcentral Alaska. A vort lobe
embedded in the flow will continue to push across Cordova and into
the panhandle ushering colder air and an enhanced pressure
gradient into the region. Elsewhere, a stratus layer over Cook
Inlet is still very visible on the latest satellite image. Areas
of Fog continues across the Anchorage Metro Area tonight.
Tomorrow, the upper ridge will move quickly across Southcentral on
Saturday. A negatively tilted trough will glide over the ridge
and become absorbed into the next trough that will be moving
onshore into Western Alaska. This new system will bring difluent
flow and upward vertical motion to central Alaska. The projected
temperature profile for this system will be favorable for an
efficient dendritic growth zone which will support a snow event
late Saturday and early Sunday. This is a fast moving system and
generally expecting 2-4 inches to blanket the Anchorage Metro Area
and the Mat-Su Valleys.

&&

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

An area of high pressure centered over Southwest Alaska will
continue to shift off to the southeast as a weak front moves into
the Kuskokwim Delta during the next 24 hours. This front is
spreading precip into this region and extends down to just north
of Hooper Bay, where precipitation coverage is more spotty.

Further north, a short-wave trough currently over eastern Siberia
is forecast to trek east towards Norton Sound before diving
southeast towards the northern Gulf of Alaska; rapidly
strengthening as it does so. What this means for Southwest Alaska
is two part. First, upper-level ascent is now becoming stronger
in the model forecasts with each successive run. Two, cold air
advection along the western flank is stronger aloft while a
faster surge is seen at the surface as northeast winds advect the
colder air down the peninsula from central portions of the state.
Meanwhile, moisture will continue to move northward into the
region from a storm system south of the Aleutian Chain.

This means a quicker transition from rain to snow is expected to
progress from northeast to southwest, especially for the Saturday
evening into Sunday morning time frame. With this in mind,
snowfall accumulations were bumped up north and east of a Aniak to
Igiguig line. Here, a few inches of snow are expected in the
valleys, with several inches possible in some of the mountains.
Further south and west, a mix of rain and snow or all snow will
"buffer" these locations with accumulations less than one inch
expected.

&&

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

Today's run of the various numerical models have trended stronger
with the trough mentioned in the above discussion while keeping
the low south of the Aleutians somewhat weaker and further south.
This has resulted in a lower precipitation amount signature along
the chain. However, widespread precipitation is still likely, just
with a somewhat lighter intensity during the next 36 hours before
the system enters the central Gulf of Alaska.

Attention then turns to a strong front entering entering the
western Bering Sea by early Sunday morning. Here too the models
remain in remarkable good agreement while trending stronger with
the frontal system. The previous shift had already ramped up POPs
and precipitation amounts and this looks good. The only change we
made here was to slow down the frontal progression slightly given
the stronger signatures seen in the model fields both at the
surface and aloft. Additionally, this system will be bumping into
a short-wave ridge ahead of it between itself and the systems
further east.

&&

.LONG TERM FORECAST (Days 3 through 7: Monday through Friday)...

As the low in the southern Gulf shifts south to the North Pacific
Monday, deep northerly flow will establish itself over the
Mainland. Expect gusty outflow winds along favorable gaps over the
northern Gulf Coast to peak Sunday night through Monday morning,
then generally subside through Tuesday. Amid the strong offshore
flow, skies will quickly clear out Monday morning from west to
east over Southcentral and a general cooling trend will set up
through the middle of the week. By Tuesday night, the ridge will
erode as a series of shortwaves approach from the west. These
shortwaves will bring some more clouds to Southcentral and a
return of the chance for some isolated showers through the end of
the week.

Over Southwest Alaska and the Bering Sea, the dominant ridge will
break down early next week. A front will push through the Bering
Sea from west to east Sunday night through Tuesday morning,
spreading rain and gale force winds eastward before weakening as
it moves onshore Tuesday. Ahead of the front, southerly flow will
bring warm air and a marine stratus layer northward. Once the
front has passed, colder air will begin to filter out of Russia
and into the Bering Sea. This will destabilize the atmosphere and
re- introduce convective showers to the Bering Sea as a series of
upper-level disturbances push east Tuesday through Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 178.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...RD