Gale Warning 163, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
550 AM AKST Sun Feb 9 2020

.ANALYSIS AND UPPER LEVELS...

There is a surface low near Kotzebue with the frontal boundary
near McGrath and Lime Village. In less than 12hrs, the temperature
at Bethel plummeted from 33F to -11F and Aniak went from 35F to
zero degrees Fahrenheit. In the wake of the frontal passage there
is a dome of high pressure at the surface southwest of Kipnuk.
There is a developing low between the Kuril Islands and Shemya.
The latest ASCAT (advanced scatterometer) pass detected gales and
storm force winds north and south of the Alaska Peninsula with
gales into Shelikof Strait early this morning. The jet is south of
the AKPEN and bisecting the Gulf Of Alaska and its core was
pegged at 150 knots. There is a second jet core of 150 knots
associated with the developing low south of the western Aleutians.

&&

.MODEL DISCUSSION...

The GFS ensemble members are tightly clustered through 48 hours
and decently grouped through 60 hours. The major synoptic features
for the GFS ensemble mean and the operational runs of the NAM,
Canadian and ECMWF are very consistent with the placement. For
initialization purposes compared the 9z radars with the
precipitation prognostics from the operational runs. The ECMWF
was too broad brushed. The Canadian, GFS and NAM faired pretty
well over southwest Alaska and Prince William Sound. There are
minor differences on the QPF side of the house but overall above
average confidence with the models for the next 2 days.

&&

.AVIATION...

PANC...VFR conditions are expected this TAF package. Overnight
both PANC and PAMR observed clouds as low as 3,200 feet although
the actual cigs were near 5,000 ft or slightly above. Through the
morning, the surface southeasterly Turnagain Arm wind will
increase and bend over the aerodrome. By 12z on the 10th winds
will start to slack off. Amendments will be made as needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Winds will slowly diminish over the area today as the weather
system responsible moves north. Southwesterly flow aloft will
continue as the upper level trough remains to the west, with some
showers over Southcentral. These will mainly be from Prince
William Sound eastward, and over the northern Susitna Valley. The
upper level trough axis will slide through the area Monday
morning from west to east. This will usher in colder and drier
air. Outflow winds will begin later tonight, and increase through
the day Monday. Skies will clear and temperatures will drop as
this new air mass moves into Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The storm over the Southwest is rapidly weakening on its
northeastward track to the interior. Scattered to numerous snow
showers will continue to develop along weak troughing along the
lee side of the Alaska and Aleutian ranges through late this
morning with snow diminishing this afternoon from south to north.
Winter weather products were ended with the morning package as
conditions are improving. Cold air advects back across the region
and will bring much colder temperatures through Tuesday.

&&

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

The next storm system is currently south of the Western Aleutians
and will be the main focus for weather tonight and Monday. This
storm will bring hurricane force wind gusts, snow and rain as it
moves across to the western Bering. High wind warnings were issued
during the morning package for the Western and Central Aleutians.
There is still some uncertainty with the timing of the strongest
winds and could come in faster than currently expected.
Precipitation should change over from snow to rain along the
front, so a brief period of blowing is possible. Cold air wraps
around the core of the low late tonight which will bring a mix of
precipitation through Monday night as the parent low slowly moves
to the north. The front moves across the the Pribilof Islands and
Alaska Peninsula on Tuesday. Precipitation types should mainly be
rain along the boundary. A colder air mass along the Pribilof
Islands will sag farther south Tuesday night which will bring
blowing snow conditions Tuesday night as southeasterly flow gusts
up to 30 mph.

&&

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

A storm force front moving across the Aleutians will diminish to
high end gales by Tuesday as it approaches the Eastern Aleutians.
Models currently disagree on whether a new low will develop along
this front in the Eastern Aleutians. If this happens, winds on the
west side will reach gale force on Thursday, but should not
increase any higher.

For the Gulf, Northwest gale force winds will continue through the Barren
Islands on Tuesday. A brief break will occur before the next low
moves northward into the Gulf. Expect gale force winds to return
late Tuesday into Wednesday and to continue into Thursday,
although the exact timing of the next low pressure system remains
uncertain

&&

.LONG TERM FORECAST (Days 3 through 7: Tuesday through Saturday)...

The beginning of the long term has a brief break in the weather
for the mainland, with yet another frontal system slowly making
its way across the Aleutians. By Wednesday, a low develops along
the front associated with the Aleutian low, which then progresses
into the Gulf of Alaska. Timing and strength on this new system
remain somewhat in question, with forecast models having poor
run-to-run consistency in recent days. At the moment, it looks
like this system will track across the Gulf of Alaska, with much
of the mainland remaining under high pressure. If this track holds
true, the chances for snow over the next week are minimal for most
of the mainland, but outflow winds, particularly in Southcentral,
will be a concern beginning late Wednesday into Thursday. By the
end of the week, forecast models become quite inconsistent on the
placement of the parent low pressure system, with the GFS keeping
it in the Western Aleutians and continuing to develop new lows
south of the Aleutian Chain, while the EC moves the parent low
into the Bering and progresses the developing fronts across the
mainland. Current thinking is that the EC solution is slightly
more likely, because the GFS has had poor-run-to-run consistency
over the past week. Either way, the outlook for the marine areas
is stormy through the end of the week, with the forecast for the
mainland more uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187 191. Winter Weather Advisory 145.
Heavy Freezing Spray 160 179 185 414 411 412.
MARINE...Gale 130 131 138 139 351 173 174 175 176 185 413 412.
Storm 177 178 411. Heavy Freezing Spray 160 179 185 414 411 412.

&&

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