Gale Warning 527, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKDT Fri Oct 11 2019

.ANALYSIS AND UPPER LEVELS...

A strong upper level low is helping to support a dynamic surface
low over the Northern Gulf of Alaska. The associated occluded
front extends north and west across Southcentral. Areas of rain
were observed over most lower elevations from the Copper River
Basin to the Cook Inlet Region. Snow or a mixture was reported at
higher elevations across Southcentral. Strong outflow conditions
with increasing pressure gradients was observed over the northern
Gulf coast and western Gulf. Gale to storm force westerly winds
were observed out of Kamishak Bay and across the Barren Islands.
High pressure building over the northeast Bering Sea brought
generally northerly flow and clearing over the Southwest Mainland.
A weakening occluded front extending east from a dissipating low
over the central Bering Sea brought light rain to the eastern
Aleutians and western Alaska Peninsula. Scattered rain showers
under broad cyclonic flow was observed over the the remainder of
the Bering Sea and Aleutians.

&&

.MODEL DISCUSSION...
Models in the short term are in fairly good agreement. Largest
and the most impactful differences will be in wind fields
associated with the remnants of Hagibis as it tracks across the
Bering Sea.

&&

.AVIATION...
PANC...VFR conditions are expected. Gusty north winds are expected
across the airport complex through tonight.

&&

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

A very impressive early season, wrapped up extratropical cyclone
is currently impacting the Southcentral region with rain as well
as some higher elevation snow. Snow levels dropped as low as 1000
feet across some areas with heavy snow in the front range of the
Chugach and parts of the Glenn Highway east of Chickaloon. The
surface low is centered around the Copper River Delta, with strong
gale force winds spreading across most of the Gulf of Alaska and
along the North Gulf Coast. These offshore winds will intensify
tonight and early Saturday as the low moves east, and cold air
advection increases from Prince William Sound eastward. Rain and
snow showers will quickly come to an end tonight with the drying
offshore flow and weakening of the upper level deformation band.
Northwest flow aloft will dominate Saturday and Sunday, with
clearing skies and colder temps infiltrating the region, with the
coolest temps on Sunday morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure will continue to build in over southwest Alaska
tonight into Saturday and then dominate the area through Sunday.
This setup will keep precipitation out over the Bering and also
bring outflow winds to the area. With the more clear skies
expected with the high pressure, temperatures are expected to drop
below freezing for most of southwest Alaska. Inland locations
will see the lowest temperatures that will reach around 20 degrees
overnight.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A low in the southern Bering will bring rain to most of the
Aleutian Islands through the night as it slowly tracks to the
east. It will then weaken Saturday and push off to the southeast.
Sunday it will phase with a North Pacific low as it approaches the
Alaska Peninsula and bring rain and gale force winds to marine
areas on the Pacific side of the Alaska Peninsula. Out west, the
remnants of Typhoon Hagibis will approach the western Aleutians
on Sunday beginning to ramp up winds and rain for the islands.

&&

.MARINE (Days 3 through 5)...

Bering Sea/Aleutians:There is high confidence that the
extratropical remnants of Typhoon Hagibis will approach the
western Aleutians by Monday and rapidly deepen to around 955mb.
Sustained hurricane force winds and heavy rains are likely in the
western Aleutians late Sunday night into early Monday, then in the
central Aleutians/southern Bering by Monday evening. Combined
seas up to 50 feet are expected. While models have varied widely
run to run, the current expectation is that the low will take a
northern turn late Monday into Tuesday, and its center will be
roughly along 60N by Wednesday. Based on the expected track,
hurricane force winds are not expected in the Pribilof Islands,
but storm force winds are likely. Winds will generally diminish
and seas will subside as the low exits to the north, however
models continue to depict a series of potent lows skirting from
the western to central Aleutians in the Tuesday to Wednesday
timeframe. But, there is high uncertainty with location. So, while
hurricane force winds should be limited to the post-tropical
cyclone, gales, or even storm force winds are likely in parts of
the Aleutians/Bering even after that feature exits.

Gulf of Alaska: Easterly gales are expected in the Gulf Monday as
a North Pacific low deepens and pushes an elongated front north.
Conditions will improve Tuesday into Wednesday, though a secondary
low may develop and bring another round of small craft winds to
the central Gulf Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The main focus in the long term is Typhoon Hagibis, which will
undergo extratropical transition in the rough Sunday timeframe,
then bomb out over the western Aleutians/Bering early Monday.
Besides the marine hazards mentioned in the marine discussion,
expect strong winds over the western Aleutians with gusts in the
70 to 80 knot range. In addition, heavy rain is likely over the
Aleutians. While models have come into better agreement with the
track of the former typhoon, there is a lot of uncertainty with
what comes after. Models generally depict a secondary low (or
perhaps series of shortwaves or closed lows) that form under the
polar front of a 160 to 170kt jet streak oriented roughly along
50 N from the Kamchatka Peninsula to the Aleutians. In any case,
unsettled weather will continue over the Aleutians and Bering at
least through midweek, likely through the end of the week as broad
cyclonic flow continues and several weak shortwaves traverse the
Bering from eastern Siberia.

Given the expected northward track of the former typhoon, weather
in the Southwest mainland will be relatively quiet in the long
term. Strong southeast winds along the west coast and heavy
precipitation at times is expected as the weakening front
associated with the typhoon reaches the mainland late Monday into
Tuesday. Otherwise, expect several weakening fronts to approach
the mainland as the week goes on, bringing bouts of precipitation.

Over Southcentral, generally dry weather is expected through
midweek. High pressure will settle over northern Alaska, and cold
conditions inland with offshore winds will dominate through
midweek. A series of fronts will move from the Gulf northward.
This will potentially bring precipitation to the North Gulf
Coast, but generally expect precipitation to stay over the marine
area. During the later part of the week, the ridge will retrograde
to the north and a wetter pattern is possible.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES: 120 130-132 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...MM