Small Craft Advisory 11, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKST Thu Jan 2 2020

.ANALYSIS AND UPPER LEVELS...
A cold upper level low which has been sitting over Bristol Bay is
now drifting southward along the Alaska Peninsula. Temperatures
across Southwest Alaska are quite frigid, generally ranging from
-15 to -40 degrees this morning. A short-wave tracking along the
 western periphery of the upper low is combining with strong
 northerly winds and cold air advection to produce blizzard
 conditions on the Pribilof Islands. Snow and blowing snow is also
 being observed across the eastern Aleutians and southern Alaska
 Peninsula. With cold air temperatures and strong winds across the
 eastern Bering Sea and Southwest Alaska coastal waters, conditions
 are ideal for heavy freezing spray.

Meanwhile, a surface low has formed south of the Alaska Peninsula
and Kodiak Island. As the upper level low drifts south this surface
low is beginning to be pulled north on the east side of the upper
low. Thus, bands of snow showers and locally gusty winds are tracking
across Kodiak Island.

A mesoscale low is lifting north across Prince William Sound,
bringing snow showers and locally gusty winds with it. Some of
this moisture is spreading over the coastal mountains, including
into Anchorage. The presence of at least some clouds over south
central Alaska has kept temperatures from falling as low as they
could with this arctic air mass in place. Temperatures across the
region generally range from -10 to +10degrees.

Lastly, a gale force front is weakening as it lifts north and east
across the far western Aleutians.

&&

.MODEL DISCUSSION...
Models are in good agreement with handling of large scale features
over the next few days. The primary forecast challenge will be
timing and location of mesoscale snow bands and associated gusty
winds, primarily with low currently over Prince William Sound and
with the low south of Kodiak Island. We will rely heavily on
satellite and radar trends to aid the short-term forecast, as
models tend to struggle with these smaller scale features.

There are also some model differences with lows tracking along
the Aleutians and southern Bering Sea Friday night through the
weekend. These look like weak lows and any impacts of stronger
winds or heavier precipitation will likely be localized to small
areas at any given time.

&&

.AVIATION...
PANC...The low moving onshore across Prince William Sound will
spread snow showers across the Kenai Peninsula and toward
Anchorage. Thus, we could see a few snow showers with reduced
visibilities through around 06Z, with potential for MVFR vis
and ceiling. After that, expect decreasing clouds. Pressure
gradients will also tighten in response to the deepening low
near Kodiak. Thus, increasing northerly winds late tonight
through Friday should prevent formation of low clouds and
maintain VFR conditions.

&&

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

A compact low moving into Prince William Sound is bringing
scattered snow showers this afternoon along coastal areas east of
Seward. These will track west over the next few hours and
potentially make it to the Anchorage area by evening, though
little to no accumulation is expected in the city. Snow showers
will taper off Friday morning with skies clearing through the day.
With generally higher pressure to the north and lower pressure to
the south, northerly synoptic winds will bring cold, Arctic air
into south central Alaska for the next several days with highs in
the single digits and lows well below zero for much of the region.

A compact low is currently approaching Kodiak Island. Snow squalls
are expected to develop this evening as onshore winds intensify.
A Winter Weather Advisory is in effect through 9 AM Friday
morning, though total accumulations could significantly vary
across the Island depending on where the heaviest squalls setup.
After a brief lull on Friday afternoon, the same pattern is
expected to redevelop overnight Friday into Saturday morning with
the same aforementioned impacts expected.

&&

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

Clearing conditions and cold temperatures will continue across Southwest
Alaska this evening as an upper level low centered over the Alaska
Peninsula slowly drifts southeast through Friday. As this low moves
out of the area overnight, a strong pressure gradient will cause gusty
winds across interior Bristol Bay, which will cause temperatures to
warm overnight. Temperatures across the region will continue to increase
slightly over the next few days.

&&

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

A gale force front over the western Aleutians this afternoon will
continue to weaken through Friday afternoon.  Strong winds over
the central and eastern Bering, along with falling snow, will keep
hazardous conditions through the night stretching from the
Pribilofs to Dutch Harbor. The Blizzard Warning for the Pribilofs
has been extended through 9pm tonight as reduced visibility to a
quarter mile and snow continue. The Winter Weather Advisory for
for Dutch Harbor has also been extended through late tonight for
strong winds and blowing snow, which could reduce visibility to a
half mile. Conditions will improve overnight and into Friday
morning. By Friday afternoon, northerly flow will keep strong
winds out of bays and passes along the eastern Aleutians and
Alaska Peninsula through Saturday.

&&

.MARINE (Days 3 through 5)...
On Saturday, a surface low across the southern Gulf keeps small craft
to gale force winds around Kodiak Island, then tapers down by
Sunday morning. The next strong storm organizes over the north
Pacific and pushes a front to the western Aleutians Sunday night.
This storm system moves slowly northeast spreading gales across
the southwest Bering through Monday night. There is still some
uncertainty on the speed and track of this system so adjustments
are likely to be made.

&&

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

Southcentral:
Dry and cold conditions will persist for south central Alaska
Saturday through next Wednesday night. The exception to this is
Kodiak Island and the Gulf coastal locations where low pressure
over the Gulf should bring enough lift to support snow this
weekend. Snow is expected to taper off on Sunday from west to
east. As this low makes its track across the Gulf, offshore flow
is expected to increase. Thompson Pass and the Copper River Delta
will experience strong northerly gusts Saturday night through
Sunday. Another weak low tracking east from the Bering could bring
additional snow to Kodiak between Sunday and Tuesday, however
there is still a bit of uncertainty on the track and timing of
this next system.

Southwest:
Dry and cold conditions are expected for Saturday with snow
chances increasing on Sunday as a weak low from the Bering pushes
inland through Monday. Drier conditions are expected on Tuesday
and Wednesday, however another Bering front approaches Tuesday
night. There is high uncertainty with the progression of this
front, but the general model trends keep the dominant ridge
influence across the Southwest.

Bering:

Across the Bering, active weather persists through the extended
forecast Saturday through next Wednesday night. A weak surface
low is expected to develop on Saturday, south of the Pribilof
Islands. Models are still not in great agreement with this
development, however the main impact from this will be snow for
the eastern waters including the eastern Aleutians to Alaska
Peninsula. The next strong storm develops across the north Pacific
and lifts north to the Western Aleutians late Sunday. This is a
warmer gale force system that moves to the southern Bering on
Monday with re-enforcing energy sending this front farther north
and east into Tuesday. Precipitation around the core of this
system will mainly be rain for the central Aleutians with mixed
precipitation for the western and eastern Aleutians. The front
moves across the Alaska Peninsula on Wednesday. Precipitation
along the front will likely start as snow and then mix with/or
change over to rain during the afternoon.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 195. Blowing Snow Advisory 185. Snow
Advisory 171.
MARINE...Gale 130 131 138 139 150 178 185.
Heavy Freezing Spray 121 127 129 130 138 139 140 141 160 165 175 179 180 185.
FIRE WEATHER...DONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KH