Blizzard in Alaska, February 10 to 12, 2021

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 PM AKST Wed Feb 10 2021

.ANALYSIS AND UPPER LEVELS...

The upper level pattern has not changed much over the past day. The
ridge in the eastern Gulf of Alaska is flattened over Southcentral
with a small axis along the AlCan border and a larger one
extending through Bristol Bay and through the northern Bering Sea.
This ridge is blocking the progression of the front in Southwest
Alaska and why it is stalling in that area.

The surface ridge is quite strong (about 1064 mb) and well
offshore in the Arctic Ocean with a sub 950 mb low south of the
Central Aleutians. This large pressure gradient is keeping the
gale-to-storm force winds across the Bering Sea which is
producing Heavy Freezing Spray near the ice edge.

&&

.MODEL DISCUSSION...
Models are finally settling into an agreement that increases
confidence in the overall forecast. The two main issues we have
been watching the past few days are the low south of the Gulf of
Alaska and the front swinging through the Bering Sea from east-
to-west Thursday through Friday. Models are all in line with that
Bering Sea front and its timing and movement. For the low south of
the Gulf of Alaska, the models are in decent agreement, and much
better than a day or two ago. However the GFS is a bit of an
outlier where it wants to move a wave northward through the
northwestern Gulf Saturday and is the only one indicating that.
Even so, looking back at the issues from Monday, it seems that the
GFS was the closest model on both the low south of the Gulf of
Alaska as well as the front in the Bering Sea. So, its solution
on this cannot be ruled out just because it is an outlier.

&&

.AVIATION...
PANC...VFR conditions and northerly winds will persist. There is
the chance for some low level wind shear (LLWS) starting Thursday
as winds aloft increase from the southeast. However, the shear
layer will most likely be above the 2000 ft LLWS threshold.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Wednesday Night through Saturday)...

The final few flakes are being squeezed out over the Susitna
Valley this afternoon as quiet and warmer conditions return to
the Southcentral mainland. Thursday should be the warmest day of
the week due to broad southerly flow, which will also keep the
skies mostly cloudy. A slow decrease in temperature and cloud
cover will begin on Friday as an upper level high over the Yukon
pulls in drier, colder air from the interior. By Saturday most of
the Southcentral mainland will enjoy sunshine and seasonal
temperatures.

Kodiak Island will be the focus of active weather through at least
Friday afternoon. Some light rain is expected this evening, which
will increase in intensity early Thursday morning as a front parks
itself overhead. Temperatures aloft are quite cold, however the
long fetch over 40F water should keep the precipitation as mostly
rain with some snow mixed in. Heavy snow is expected above ~500
ft, with accumulations up to 25 inches expected. Slight
perturbations in the flow may cause some periods of heavy snow at
lower elevations through Friday morning. Accumulation from these
events will be negligible due to temperatures ranging from 35F to
40F. A closed low is expected to form along the front to the
southeast of Kodiak early Friday morning. This will help to pull
in colder air from the northeast by Friday afternoon, which should
switch the predominant precipitation type to snow. By this time
there won't be too much moisture left over, so accumulation at sea
level should remain in the realm of two inches by Saturday morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3:
Wednesday Afternoon through Saturday)...

The upper level ridge has moved north towards the interior as a
shortwave supporting a warm front moves up from the south. The
front will move into Bristol Bay tonight and continue to produce
light snow in the Kuskokwim Delta and Kilbuck Mountains. Winds
will continue to increase through Thursday as a stronger shortwave
and frontal system moves towards the area Thursday afternoon
through the evening hours this will tighten up the pressure
gradient even more with very gusty winds and blowing snow. As the
front pushes north and west temperatures will warm into the 30s
which will put an end to the blowing snow Thursday evening in the
Kuskokwim Delta. The snow will also end as the front pushes
northwest. A winter weather advisory continues through
Thursday evening for coastal areas of the Kuskokwim Delta, it may
need to be extended if temperatures are slow to warm up as it
will remain windy through at least midnight.

Friday the area will dry out and winds will decrease with
lingering clouds and temperatures in the upper 20s to the 30s.
Saturday will feature quiet weather with temperatures a bit
cooler.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Wednesday Afternoon through Saturday)...

The active pattern continues for the foreseeable future across the
Bering and Aleutians as low pressure dominates much of the area as
the upper level ridge has been pushed north from roughly St
Matthew Island and south and east towards the Gulf.

Widespread Gales will continue through Thursday across much of the
Bering as well as heavy freezing spray across the northern Bering.
A low will form along the front moving across the AKPEN tomorrow
and swinging across the eastern Bering this will bring a swath of
storm force winds south of the AKPEN tonight and moving into
Bristol Bay and the eastern Bering Thursday morning. The front
will push north and west Thursday and by Thursday night the front
will be near Nunivak Island and extending southwest just north of
St Paul Island. Behind this front will be slightly warmer air and
decreasing winds on Friday with small crafts across much of the
Bering with a few lingering areas of Gales especially in the
eastern and western Bering Sea. Saturday a complex low pressure
system will approach the central and eastern Aleutians with a
storm force low spreading gales and storm force winds into the
eastern Aleutians and AKPEN Saturday morning and spreading into
the southern Bering Sea. Gales will also increase from south to
north across much of the Bering with an increasing threat of heavy
freezing spray in the northern Bering on Saturday which may once
again impact fishing operations in the northern Bering this
weekend.

&&

.MARINE (Days 3 through 5)... Saturday through Monday...

Bering Sea: Heavy freezing spray is likely in the northern Bering
Sea near the ice edge. Widespread gale force winds and waves with
local areas of high end gale force winds nearly cover the Bering
through Sunday. Wave heights for the eastern Aleutians, Alaska
Peninsula and Bering over 20 feet. The Western Bering will have
wave heights over 30 feet Sunday and then subside on Monday.

Gulf of Alaska: Models are in good agreement with a strong front
diminishing early Saturday. Gustier winds linger through the
Barren Island and Shelikof Strait through late Saturday. A new
band of gale force winds and waves moves into the Southwest Gulf
early Sunday. Wave heights to 26 feet east of Kodiak Island
subsiding Saturday. A new area of waves to 20 feet build
Southwest of Sitkinak for Sunday. The models diverge past Sunday
bringing an element of uncertainty for the Gulf.

&&

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

There is a fair amount of divergence with the model solutions
that amplifies with time. There are a few items that can be
gleaned. Cold air will continue to advect from Russia towards the
Western Aleutians. There will be 2-3 lows impacting the Bering and
Aleutians. The ridge is going to start breaking down allowing for
a more progressive pattern. Some of the energy from the Bering
and North Pacific storms will get kicked towards Kodiak, the
Western Aleutian Range and the Gulf. The Canadian and the GFS are
spinning up an arctic front that will push across Southcentral late in
the period on Thursday/Friday. Multiple models were blended to
produce the long term forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Storm Warning 150 160 180 181 185 411 412 130 131 132
		 Heavy Freezing Spray Warning 180 185 414 139
		 Gale Warning 155 165 170 171 172 173 175 177 178 179 413
 					  414 351 352 119 120 136-139.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...PJS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
702 PM AKST WED FEB 10 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0458 PM     SNOW             3 SW MEADOW LAKES       61.59N 149.66W
02/10/2021  M6.5 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            TOTAL SNOW AMOUNT OF 6.5 INCHES SINCE THIS
            MORNING.

&&