Small Craft Advisory 7, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKST Wed Jan 1 2020

.ANALYSIS AND UPPER LEVELS...
A deep and cold upper level low is nearly stationary over the
Bristol Bay area. A trough axis extending east from the low
center is weakening as it lifts northward and westward back
overtop of the low center. Snow along and ahead of this trough
over Southcentral Alaska has diminished, with just some areas
of light snow or flurries remaining. A second short-wave trough
extends northwestward from the low center and is rotating
southwestward across the Kuskokwim Delta, leading to light snow.
The most impactful portion of this storm is on the back side of
the upper low, with strong cold air advection and heavy snow
showers across the eastern Bering, portions of the Southwest
coast, the Alaska Peninsula, and into the western Gulf and
southern Cook Inlet/Kachemak Bay. This is leading to blizzard
conditions for many of the land areas. This has been quite the
prolonged blizzard (18 hours or longer) for the north side of the
Alaska Peninsula (Pilot Point, Port Heiden, Nelson Lagoon, Cold
Bay) as well as the north side of Kachemak Bay (Homer). Out over
the marine areas are widespread gusty winds, bands of heavy snow
showers, and heavy freezing spray.

Temperatures are below freezing for the entire forecast area,
from the Aleutian Islands to the southern mainland of Alaska.
The coldest air is sitting over Southwest Alaska, with widespread
sub- zero temperatures. Interestingly, the warmest location in
Southcentral is the Copper River Basin (in the 20s). This is due
to the fact the cold air is advecting in from the south and west.
Thus, temperatures will quickly drop across the Copper Basin this
afternoon through tonight.

The only place with quiet weather is the central to western
Aleutians, where high pressure is leading to light winds and just
a few light snow showers. A gale force front over the northwest
Pacific is slowly approaching the far western Aleutians.

&&

.MODEL DISCUSSION...
Model solutions all show the same general evolution of the pattern
the next few days, as the upper level low in Bristol Bay slowly
exits eastward across the Gulf. However, there are some
differences with the short-waves rotating around the low as well
as with development of a secondary closed low over Southcentral.
This creates challenges for snow, which will primarily remain to
the south, from the Alaska Peninsula to the Gulf and Kodiak
Island. Variable cloud cover with the various upper waves also
leads to uncertainty in temperatures, as the presence of cloud
cover moderates temperatures. Lastly, this type of air mass is
conducive for low cloud and fog formation, which will also depend
on whether there are mid to upper level clouds. Despite the
challenges, forecast confidence is about average.

&&

.AVIATION...
PANC...While most of the snow is over, there could be an
occasional snow shower triggered by weak short-waves rotating
around the upper low center. On the other hand, if clouds clear
out in between waves, formation of low clouds and/or fog is
likely. Thus, overall forecast confidence is low. Current forecast
will carry periods of VFR along with hints of fog and low clouds
during the time most likely to be free of upper level clouds.

&&

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

Snow and blowing are continuing this afternoon across the
southwestern Kenai Peninsula under a weakening low. Onshore snow
showers are also occurring across eastern Prince William Sound
near Cordova as well as portions of Kodiak Island. Conditions
will improve this evening for both these areas as onshore winds
will diminish, though scattered snow showers will persist along
coastal areas through Thursday. Elsewhere, snow has ended across
the rest of Southcentral and cold temperatures continue to build
into the region. There is a slight chance of fog overnight tonight
if more clearing occurs than expected. Otherwise partly to mostly
cloudy skies and below average temperatures will persist through
Friday, again with the exception of snow redeveloping across
Kodiak Island as another low approaches from the south.

&&

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

Broad cold air advection behind the upper level trough swinging
south across the Bering continues to hammer the coastal locations
along the Kuskokwim Delta coast. Visibilities near Toksook have
gone between 1/4 mile and 0 miles for nearly 24 hours, coupled
with unrelenting 40 mph winds. The tight pressure gradient will
slack later this evening, allowing winds to ease and conditions to
markedly improve. Moving into tomorrow and tomorrow night, winds
will turn northeast and offshore flow will dominate. Skies will
clear out from King Salmon and north and overnight temperatures
will drop. Interior locations near Sleetmute should see -25 or
colder. King Salmon to Dillingham through Bethel will drop to the
lower negative teens.

&&

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

Broad north to northwest flow will persist through the forecast
period. Strong north winds will be a mainstay through Friday, with
typical on and off snow showers throughout the entire Bering.
Ridging will build in from Adak west, providing a reprieve until
an occluded front brings snow showers back to the western
Aleutians at the end of the week.

&&

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

A relatively quiet weather pattern sets up for this time of year
all across southern Alaska and the Bering. A low over the southern
Gulf of Alaska moves into the eastern Gulf Saturday, with a
chance of some northwesterly gales through the Barren Islands. A
new North Pacific low may move into the southern Gulf on Sunday,
but there is substantial model disagreement, and confidence in
that is low.

High pressure will keep all winds below gale force all across the
Bering Sea. Winds may approach gale force in the western
Bering/Aleutians Sunday night as a strong low approaches. There
is limited confidence as to the track of this low through Monday
night, however, confidence is high that gales will cross into the
eastern Bering/Aleutians by then.

&&

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

A quieter weather pattern is setting up for much of southern
Alaska in the long-term period as a cold air mass becomes firmly
planted across the area. This will divert the storm track to the
northern Pacific with any lows impacting the Panhandle. This is
generally agreed upon between models.

A weak low centered off the coast of Kodiak, over the
southwestern Gulf, will slowly move eastward across the southern
Gulf and into the eastern Gulf on Saturday. On Sunday, a new North
Pacific low may approach the Alaska Peninsula and Kodiak, but
there is substantial model disagreement on this. There is much
better agreement on the leading front of a strong North Pacific
low moving into the western Aleutians on Monday. The front should
slowly track across the southern Bering and into the eastern
Bering by Wednesday.

Elsewhere, cold and dry will be the prevailing conditions across
mainland Alaska, which means the main weather hazard will be
strong gap winds, particularly through Thompson Pass, but also
possibly through the Matanuska Valley. These winds coupled with
the cold air may lead to wind chill concerns, which unlike
previous days, will focus more on Southcentral rather than
southwest Alaska. Polar air will continue to drift southward
across the Bering through the weekend, however, winds will begin
to diminish to light and variable to start the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 181 195
MARINE...Gales...130 132 138 139 150 155 160 165 170 171 172 173
174 178 179 180 181 185 352 412 413 414
Heavy Freezing Spray 130 131 132 136 137 138 139 140 141 160 165
179 180 181 185 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS
MARINE/LONG TERM...CK/JW