Small Craft Advisory 97, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...RESENT
National Weather Service Anchorage AK
505 PM AKST Wed Jan 30 2019

.ANALYSIS AND UPPER LEVELS...
There is an upper level low over Southwest Alaska extending into
the western and northern Gulf. This is producing some showers
around Southcentral, which are sporadic and fairly light. There is
also a considerable amount of low stratus and some fog. An
associated surface low is centered just to the southeast of the
Kenai Peninsula. There is an upper level ridge over northwest
Alaska, which is drifting towards the southeast. There is a
negatively tilted ridge over the central/eastern Aleutians and
southern Bering Sea. There is an upper low southwest of the
western Aleutians. There are a couple of strong surface lows
associated with this upper low, one is near the upper low center,
the other is south of the western Aleutians and moving northward.
There is an upper low over northwest Canada, with strong northerly
flow aloft developing over eastern Alaska.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for the short term
portion of the forecast (Friday afternoon). The models have been
trending further eastward with a vort max moving southward into
the Copper River Basin Thursday night and Friday, now showing it
just clipping the eastern Basin on Friday. Thus winds will have to
be lowered a bit. There are also some minor timing differences on
a front moving into the Gulf from the west Friday afternoon.
There are also some minor differences for the location of a
surface low over the western and central Aleutians Friday
afternoon. Over all, the forecast confidence is higher than
normal.

&&

.AVIATION...
PANC...MVFR to possible IFR conditions in fog and low clouds are
expected through Thursday morning. Conditions should improve
Thursday afternoon as drier air moves into the area.

&&

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

Tonight's primary weather hazard for much of Southcentral is the
continuation of area fog for much of the lower elevation areas. As
is typical, when the winds died off after the last round of rain
and snow last night, fog developed quite quickly behind it. The
fog is likely to persist for much of the overnight. The fog may
continue for much of the day Thursday over the Kenai Peninsula.

The next weather focus will be on an incoming blast of cold air
expected to move south across the Alaska Range into Southcentral.
Fortunately, in the upper levels the trends in the guidance have
continued to shift the wave that would have been capable of
producing very strong winds through the gaps further east. Thus,
the most significant changes to the forecast have been to begin to
lower the expected winds through many of the gaps, especially the
western-most ones. Windy conditions are still expected, especially
from late Thursday afternoon through early Friday morning, but
they are not forecast to be quite as strong. With that said, one
area of increased concern is around Thompson Pass. Despite
otherwise sunny conditions, recent significant snowfall is highly
likely to become transportable as the winds increase with gusts to
60 mph. Thus, a Winter Weather Advisory for blowing snow has been
issued as localized whiteout conditions will be possible from
tonight as the winds begin to increase through Friday morning,
when the winds begin to subside.

Temperatures will fall back to normal or even a few degrees below
normal on Friday and Saturday as the cold air settles in. Dry
conditions are expected area-wide with plentiful sunshine Thursday
and Friday. The next front approaches from the west late on
Saturday which will once again increase the cloud cover, but most
of the precipitation is expected to remain from Kodiak west as the
front weakens rapidly before it makes it to more populated areas.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
An upper high over eastern Siberia and an Arctic upper low over
northeast Alaska and the Yukon will maintain weak offshore flow
and cold and dry conditions through Thursday. Parts of the
Kuskokwim Delta never broke out of fog today, and expect patchy
fog to develop further overnight into Thursday morning in the
Kuskokwim Delta and along Bristol Bay coast. During the day
Thursday, northeast flow should strengthen enough to clear out
fog.

A transition to south flow with slightly warmer, wetter weather
is expected Friday as a front associated with a storm force low
over the western Bering approaches Southwest. The front will
dissipate as it reaches the mainland so significant precipitation
is unlikely, with around 2 inches of snow expected in areas closer
to the coast and up to an inch farther inland. Another storm force
low will reach the western Aleutians late Friday into Saturday,
and warm air advection ahead of its front will continue the warm
up Saturday, with another round of precipitation. Again, the front
will be dissipating as it reaches the mainland but still expect
some precipitation, though with the continuing warm-up, will
probably see areas of rain or rain/snow mix.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A storm force low roughly 350 miles southwest of Attu is already
bringing low end gales to the western Aleutians, and expect winds
to ramp up to storm force over the western Aleutians later tonight
as the low deepens and shifts northward, while widespread gales
will set in over the central Aleutians and central and western
Bering. Winds and precipitation will diminish during the day
Friday, then another storm force low will impact the Aleutians
and Bering late Friday into Saturday. This low is the progression
of a wave currently over eastern China, and models have some
discrepancies with the setup of the low as it reaches the
Aleutians.

&&

.MARINE (Days 3 through 5)...

The global models continue to show a series of lows developing in
quick succession for the Bering and Aleutians. The pattern actually
holds up for 10 days. Suffice to say, very confident in the
notion of cyclones developing south of the Aleutians, jumping the
chain and then unleashing strong winds/rough seas into the region.
Very confident in how quickly the storms follow in the wake of
their predecessors. At the beginning of this forecast period 00z
Saturday, there is a surface low near Kamchatka with an estimated
pressure of 954 mb and a second surface low west of Adak ranging
from 960 mb - 966 mb which is enough to make a difference between
gale or storm force winds materializing. By 12z Saturday the low
west of Adak moves due north and then is west of St.Paul. The GFS
and the ECMWF both prog that track but the GFS definitely intensifies
the low more than the ECMWF. Meanwhile the Kamchatka low slowly
decays wobbles around the western Bering. But there is another
slug of vorticity propagating about the base of the longwave
trough that support a new low moving west of Adak 18z Sunday. Also
at 18z Sunday, looking further down range there is a new low in
the Sea Of Japan that is going to undergo rapid cyclogenesis once
it moves over the Kuroshio Current and it is headed directly to
Attu Island.

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

The longwave pattern features a ridge from the Central Pacific
into Southwestern Alaska with the longwave trough over Kamchatka
and the Northwest Pacific. As time elapses, the troughing extends
eastward encompassing more of the Bering while the ridge axis
shifts over Southcentral AK. This is going to result in a prolonged
period of southwest flow and moisture advection over the AKPEN
and SW AK. There are numerous shortwaves embedded in the longwave
pattern. Expect this forecast period to be highly active over the
Aleutians/Bering with 3 distinct baroclinic fronts moving across
the chain and into Southwest Alaska resulting in above normal
level of precipitation. There is growing confidence that this
mean pattern actually holds through Day 10. And guidance from the
Climate Prediction Center actually suggests that it will hold
through Day 14.

With that ridge in place over the Central Pacific, what is less
clear is how much remnant moisture will work its way into
Southcentral Alaska. At this time, Sunday looks like the best
chance for precipitation in the Anchorage Metro Area and the
forecast thermal profiles are suggesting it will be snow! Places
like Kodiak, Homer and Seward could see more of a rain/snow mix.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 176 177 178
		 Gale Warning 127 170 172 173 174 175 179 185.
		 Heavy Freezing Spray Warning 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...PS