Small Craft Advisory 142, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 AM AKST Tue Feb 11 2020

.ANALYSIS AND UPPER LEVELS...

On satellite imagery there is a frontal boundary over the central
Aleutians with a new wave developing near Atka. The original low
that anchored the occlusion is filling and is near Attu Island.
Remnants of the occlusion span from the Western Aleutians to NE
Russia and into portions of western Alaska. There is another low
spinning up east of Japan. Most of the Gulf Of Alaska and
Southcentral is under clear skies. There is a jet core east of
Cordova and a second jet core well south of the chain associated
with the system east of Japan. The latest ASCAT (advanced
scatterometer) pass has detected gale force winds over the Barren
Islands and a few gales associated with the front in the Central
Aleutians.

&&

.MODEL DISCUSSION...

The ensemble members of the GFS are tightly grouped through 24
hrs and beyond that problems emerge in the North Pacific. The
ensembles and the operational runs all show a progressive pattern
with back to back lows impacting the Aleutians and the Gulf Of
Alaska but the timing of the low tracks is clearly out of sync.
Since these storms have modified tropical moisture associated
with them the differences will ultimately impacted the level of
precision with identifying which locations will get a wintry mix
(rain/snow combo). The areas of concern will be the Central
Aleutians, AKPEN, Kodiak and Prince William Sound. The models all
ping into arctic air banked up against the Alaska Range with some
of the arctic air seeping into Southcentral.

&&

.AVIATION...

PANC...VFR conditions are expected this TAF package. There is a
low pressure system that is moving towards Southcentral, however
the leading edge of the precipitation shield is not expected to
reach the aerodrome this TAF package. "Down Inlet" flow will
continue and northerly wind will continue over PANC through 6z
Thursday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure at the surface and aloft will remain over the
Southcentral mainland today. Offshore winds will diminish during
the day as the surface gradient relaxes. A fairly strong system
will move into the Gulf of Alaska from the south today.
Precipitation and increasing winds will reach Kodiak Island this
afternoon and increase this evening. The precipitation will start
as snow on Kodiak, with some blowing snow. This will mix with or
change to rain later in the night through Wednesday morning.
Precipitation will reach the Kenai Peninsula Tuesday evening, and
move inland Tuesday night and Wednesday. The best chances for snow
are along the Gulf Coast, and Inland through the Copper River
Basin. Areas from northern Cook Inlet through the Susitna valley
have a chance of snow, but accumulations look unlikely at this
time.

&&

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

Weak low pressure is currently pushing into Southwest Alaska. The
cirrus shield of this system can be well seen on satellite. This
low is mostly a mid to upper level low and is not being reflected
at the surface. In fact, winds in southwest Alaska are generally
northeasterly as the mid level cloud cover of this low rides over
the top of cold air. So not much will amount from current weather,
save for a slight warm-up...therefore little adjustment was made
to the forecast tonight.

Later today into Wednesday a second low pressure will slide east
across the AKPEN. This should bring a shot of snow to the Bristol
Bay area. More importantly, winds wrapping around the backside of
the low will strengthen northeasterly flow for all of Southwest
AK, especially Wednesday night into Thursday. Temperatures will
drop as well as they are drawn south from the Interior. Right now
we do not expect wind chill to meet advisory criteria, but be
prepared for it to get cold again.

&&

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

Low pressure in the far Western Bering continues to hang a weak
front across the Western Bering/Aleutians. Some gale force winds
are still expected from it today though. This low will drift
northwest and decay through Wednesday. Meanwhile, strong
northeasterly flow will begin to setup late today in the eastern
Bering and be in full force Wednesday. This will make for an
interesting wind pattern in the central Bering as this northeasterly
flow collides with the front out west. This amounts to sharply
shifting wind and some areas of gale force in the central Bering
as these two air masses compete for real estate in the Bering.

Wednesday into Thursday a more powerful low pressure system is
expected to work its way north out of the north Pacific and across
the western Aleutians into the Bering. As of now, we have it to
bring storm force winds with it. However, models are hinting at
some stronger winds, so we will continue to hone the wind forecast
with this system. This low will be the next big weather maker for
the Bering Sea, so stay tuned to the forecast.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

A strong storm will be moving across the central Aleutians into
the central Bering Sea Thursday and Friday then weaken Sunday.
Gale force wind can be expected north of the low and in advance of
it's front Thursday and Friday. Gale force west and southwest wind
is likely south of this low as it crosses the Aleutians Friday.

Over the Gulf of Alaska, winds will remain below gale force
Thursday through Saturday.

&&

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

A strong ~960mb storm crosses the central Aleutians Thursday,
moving into the central Bering Sea as it weakens. This storm will
push a front through the Aleutians and Alaska Peninsula that will
then elongate to the east as a triple point low forms along it
near Kodiak Thursday night. The main low over the Bering Sea will
gradually weaken through Friday and Saturday. The models diverge
on the location of the center Friday and Saturday and also begin
to diverge significantly Saturday night and Sunday with respect to
the remnants of this storm and the approach of the next strong
Aleutian and Bering Sea storm Sunday. The latest model runs
support a much stronger storm than the previous solutions, but
also diverge on the location of the storm center. Confidence in
the extended forecast beyond Saturday is low due to the varied and
significantly differing solutions. The approach will be to
maintain the current forecast solutions with adjustments trending
toward the ECMWF solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 119 120 130 131 132 136 137 138 139 351 352 411 412
413 414 150 155 160 170 172 173 174 175 176 177 178 179. Heavy
Freezing Spray 121 129 139 414 412 160 155 150.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...SA