Small Craft Advisory 75, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
918 PM AKST Wed Jan 23 2019

.ANALYSIS AND UPPER LEVELS...
A large upper level low is centered over the western Aleutians
with a trough extending to the east into the Gulf of Alaska and a
strong ridge of high pressure aloft through the Panhandle into the
eastern interior. At the surface a strong front is currently
moving inland along the North Gulf Coast bringing rain and snow to
most coastal areas along with strong winds. Strong gap flow wind
is currently evident across Turnagain Arm/Portage Valley,
Matanuska Valley, and will be increasing out of the Knik River,
and along the Copper River as the front heads north this evening.
A second surface low about 600 nm south of Kodiak and its
associated weather front is hot on the heals of the current
system, heading north toward Kodiak Island. A 977 mb surface low
is south of Unalaska moving north and the main anchoring surface
low is about 300 nm north of Adak around 968 mb. This low is
dragging colder air back into the western Bering Sea and western
Aleutians, while on the east side of this system much warmer air
has pushed over the southern mainland.

&&

.MODEL DISCUSSION...
Consensus between the models still remains poor overall for the
Thursday/Friday timeframe over the Gulf. The NAM/GFS continue
bring a storm force low north into the Gulf Thursday and Thursday
night while the ECMWF/CAN NH have a much weaker and faster low.
The run to run consistency of the GFS appears to be better. So
will be leaning that way on this forecast package.

&&

.AVIATION...
PANC...VFR conditions should prevail through Thursday with a few
periods isolated mixed showers. Gusty Southeast winds across the
airport complex which will develop by the late afternoon and
continue into the late evening hours. After that LLWS will
redevelop across the airport complex as the surface flow will
shift to the north while winds above the surface become strong
southeasterly.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Tonight
through Friday)...
A front stalled along the northern gulf coast pulls inland
tonight as an upper level wave extending from the Bering low lifts
north. This will spread light snow inland, however a few
localized areas which warmed today could see a mix...mainly along
the Matanuska Valley and surrounding areas. Flow generally out
south to east across the Gulf brings gusty conditions across the
east to west oriented gaps through Friday as two more fronts push
to the coast...winds will slacken briefly between fronts.

The biggest change was made to increase winds for Friday. Storm
force winds are now expected to rapidly increase across the
central Gulf Thursday night as a 150 knot jet noses the next storm
system toward the southern mainland.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The front that brought a mix of rain and snow to southwest Alaska
is exiting off to the north and will be replaced by weak ridging
that will clear out any remaining showers this evening. However,
the ridging will be short lived as another front will move in over
the area late tonight. This front will bring more warm air which
will transition the precipitation, that will primarily start as
snow, over to rain for southern locations. Showers will last
through Thursday but uncertainty with the next system approaching
from the North Pacific lowers confidence in what will happen
Thursday night into Friday. The models are struggling with the
position of the low that will play a big factor in temperatures
across the area and how much precipitation will fall for
southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The low over the western Bering will slowly track south towards
the western Aleutians where it will stay in that vicinity as it
weakens into Friday. This setup will keep a mix of rain and snow
showers over the area into Friday with the strongest winds tonight
that will taper off Thursday. The central and eastern Bering will
see a series of lows track through the area from the south
bringing more showers to the region and warmer air to eastern
locations. On Friday a stronger low will approach the central
Aleutians from the south bringing another push of warm air to the
area and gale force winds to marine areas around the central and
eastern Aleutians.

&&

.MARINE (Days 3 through 5)...
The weekend will see another round of low pressure in the Bering
Sea. Model guidance is not consistent, but have decided on a
forecast based on the American models. Both models have the low in
the Bering Saturday being a large and powerful one, with storm
force winds likely for the Central Bering/Aleutians, so have added
them to the forecast. We will have to hone this area of winds
over the next couple of days. The large size of this low also
means gale force winds will encompass most of the Bering Sea and
Aleutians Saturday into Sunday, with winds beginning to taper
Sunday. In the Gulf of Alaska, remnants of a low moving through
will keep gales in the northwest gulf until Saturday, with strong
winds in Shelikof Strait as well. Things will quiet a bit after
that, but another round of winds in association with the low over
the Bering will make it into the western gulf Saturday into
Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Seeing as how models can't agree farther out than two days,
confidence is low when we move into the long term with the
forecast. In coordination with WPC this morning, the solution in
the long term is to base the forecast off of ensemble guidance. We
agree with the WPC solution, so will lean that way going forward
with the forecast. Major features were able to be discerned in the
longterm, with ridging over AK on Saturday and another large low
entering the Bering Sea. After the low exits Monday, ridging is
anticipated to build in over much of the forecast area, with a
trough over the western Aleutians. Of course, details cannot be
defined at this time, so a broad brush approach was taken to the
forecast. Stay tuned as things will likely change.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 119 120 131.
 Gale Warning 125 129 130 132 136>139 150 155 165 170 178 185.
 Heavy Freezing Spray 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...BB