High Wind in Alaska, October 30, 2016

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 PM AKDT SAT OCT 29 2016

.ANALYSIS AND UPPER LEVELS...
A very amplified upper level pattern continues to bring active
weather throughout the Bering Sea and west Mainland. The remnants
of the gale force system that moved trough the Bering yesterday
continues to slowly dissipate just off the Russian coast, while a
deeper and more significant system is quickly approaching
central Aleutians behind it. This system is expected to deepen to
near hurricane force by this evening while it moves into the
Aleutians, and will then bring active weather to much of the
Bering Sea region into early next week. To the east of this low, a
deep southerly jet along with the remnants of the front from the
weakening Bering low is bringing widespread cloud cover, rain
showers, and gusty gap winds to the north Gulf Coast and Southcentral.
So far downsloping from the Chugach has left the Anchorage Bowl
and Matanuska Valley mostly dry, but this is expected to moisten a
bit this evening as downsloping begins to weaken. Just east of the
jet, a skinny but persistent ridge stretching from the eastern
Gulf to the east Mainland is preventing the jet and associated
front over the Gulf from moving any further to the east. This is
leaving much of the south Mainland in a very stagnant pattern
with little change in the current conditions over the next 48
hours.

&&

.MODEL DISCUSSION...
The models are in very good synoptic agreement through the
weekend, especially with the track and strength of the hurricane
force low tracking through the Aleutians. As a result there is
very good confidence in the forecast over the Aleutians/Bering
Sea through the weekend. One of the big challenges that the
models aren't handling that well is how quickly ridging over the
eastern Gulf weakens, and as a result there are some timing
differences in rainfall over the north Gulf/Southcentral. Due to
the strength of this ridge the slower GFS/EC solutions were
preferred today, rather than the quicker solution from the
NAM/ARW.

&&

.AVIATION...
PANC...Conditions should remain VFR with ceilings hovering around
5000 ft through Sun afternoon as -SHRA pass through the area.
Gusty SE winds out of Turnagain Arm will also bring periods of
weak LLWS through early this evening (mainly to approaches over
Cook Inlet). This winds are expected to remain just off the
surface and will begin to weaken after 02z. SE winds will then
redevelop through Turnagain Arm starting Sun afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The front will remain nearly stationary over south central Alaska
through Monday afternoon. The front will progressively become
more negatively tilted as an upper level trough digs into the
southern Gulf of Alaska. This trough is associated with the strong
low currently over the Aleutians. As the trough moves into the
Gulf, the front will push into Kodiak Island Sunday night and
Monday. Temperatures across the area will remain well above
normal. The precipitation pattern will be the standard
upslope/downslope with most falling along and near the Gulf coast
as well as the western Susitna Valley. Most areas will see rain
rather than snow with very high freezing levels. The exception is
the Copper River Basin, which will have a slight chance of snow
and even freezing rain tonight, before drying out on Sunday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The next frontal system will reach the Alaska Peninsula Sunday
morning bringing another round of strong gusty southerly winds and
heavy rain. The frontal system will reach the Southwest Mainland
coast Sunday afternoon with precipitation spreading inland through
the evening. Additional frontal bands and troughs rotating around
the Bering low will swing into Southwest Alaska Sunday night
through Monday as the large upper level low drifts north.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Models have weakened the incoming North Pacific low slightly over
the last couple of runs and shifted it slightly south, but it
still remains a rather potent feature. The frontal system will
approach this evening with the surface low crossing the Central
Aleutians tonight and swinging into the southern Bering Sunday
morning. While this system will bring solid storm force winds to a
many areas the strongest winds look to be in the area of west to
northwesterly winds associated with the second wrap of the frontal
system behind the low. Have continued the High Wind Warning for
the Central Aleutians as this feature pushes through and the cold
advection behind the low helps to mix the stronger winds down to
the surface. The low will become vertically stacked Sunday as it
tracks into the Bering and then turns north to pass just to the
east of the Pribilof Islands.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The Bering/Aleutians remains under the influence of a 953 mb
storm force low located just northeast of Saint Paul Island by
Monday morning. This system exits the Bering Sea into the Eastern
Siberian region by Tuesday night. The upper levels keep a broad
closed low in the central/western Bering through Friday. This
synoptic feature aids in several weak surface lows developing in
the aforementioned region before phasing into one broad low
located in northern Bering by end of next week. Therefore, look
for a showery weather regime for the Bering/Aleutians region
through Friday. While on the North Pacific side, a fast-moving
low tracks along the Western Aleutians by Monday night before
exiting past the Central Aleutians by Tuesday afternoon into the
North Pacific. Meanwhile, the Southcentral region will have drier
downsloping conditions through next week. While the northern
coastal communities receiving the majority of the precipitation as
a low develops just northeast of Kodiak Island by Tuesday morning.
This system dissipates, but a secondary low develops in the
eastern Gulf before tracking to the northern Gulf by Wednesday
morning. These two synoptic systems will bring southeasterly to
easterly gale force winds to the northern Gulf, and coastal
communities accompanied by widespread rain to the aforementioned
region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High wind warning 187.
MARINE...Hurricane Force 174 176. Storms 155 165 170 171 172 173
175 177 179 180 413 414. Gales 132 150 160 178 181 185 412.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PD