Small Craft Advisory 83, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
509 AM AKST Sat Jan 26 2019

.ANALYSIS AND UPPER LEVELS...

The upper levels show a highly amplified and progressive pattern
as a broad long wave trough is seen over the western Bering while
a large ridge is seen over the US West coast extending north
towards the ALCAN border. A very strong upper level jet is driving
north from nearly 30N and riding over the top of the ridge over
the Yukon. Satellite imagery shows a long plume of moisture
associated with the jet pushing north towards the Alaskan
Panhandle with connections nearly as far south as the Hawaiian
Islands. Another strong southerly jet over the eastern Bering is
helping to support the development of a strong North Pacific low
currently moving north just south of Adak. Scatterometer data
shows a large swath of southerly gale force winds underneath the
jet pushing across the eastern Aleutians and western AKPEN. A
shortwave ridge has formed in between the two strong jets and is
currently pushing east over the southern mainland, bringing a
short period of relatively quiet weather to the area.
Southwesterly flow at the surface over Southcentral is still
leading to showers over the North Gulf coast as well as up the
Cook Inlet into the Matanuska Valley and Talkeetna Mountains, as
evidenced on radar.

&&

.MODEL DISCUSSION...

Models are in good agreement this morning with the overall
synoptic features, including ridging moving over Southcentral and
a strong North Pacific low and associated frontal system moving
north across the eastern Bering and southwest mainland. Models are
in surprisingly good agreement regarding the strength and
location of a storm force Pacific low pushing across the western
Aleutians Sunday night, thus forecaster confidence is above
average.

&&

.AVIATION...
PANC...High pressure moving over the terminal today will lead to
predominately VFR conditions with diminishing southerly winds over
the terminal. There could be a brief period of MVFR conditions
with showers later this morning but confidence is on the lower
end, thus just added vicinity showers and scattered MVFR cloud
deck.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The southerly winds over most of Southcentral Alaska have
diminished as the strong low from yesterday is now dissipating in
the Chukchi Sea. Weak ridging is over the region today but the
overall flow is still warm and southerly. Some weak isentropic
lift over Cook Inlet is keeping some clouds over the Inlet with a
few isolated rain or snow showers as well.

A short wave will ride over the ridge this afternoon bringing a
chance for some snow in the Susitna Valley.

There will be some clearing overnight over the area and this may
set the stage for the development of some low clouds and fog at
lower elevations inland and along Cook Inlet. Model guidance is
not indicating the development of fog, but the abundant moisture
from yesterday's rain and the warm temperatures aloft make it a
set up that often produces fog and/or stratus.

A front is approaching Kodiak from the west, but the high pressure
in the Gulf will likely keep the precipitation from the front to
the west of the island. On Sunday, a low will move into the Gulf
from the south and that will become the source of rain for Kodiak
Island and rain and snow along the north Gulf coast by Sunday
night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Sat and Sun)...
The well-advertised warm front is approaching the coast this
morning. South to southeast winds have remained breezy overnight
in advance of this system and should only continue to increase as
the pressure gradient tightens even more. Temperatures have
remained rather warm overnight with the winds and most locations
are hovering at or just below freezing. Thus, while precipitation
could start as some light snow, we expect a fairly quick
transition over to rain through the morning hours as temperatures
shoot up to the mid 30s and low 40s across the entire area.

Heading into Sun, the primary low will continue to push towards
the coast. This will keep SW AK in moderate southerly flow with
gusty conditions over higher elevations. This will make for
another relatively warm day across the region. There will be two
most likely spots to get precipitation on Sun. The first will be
under a deformation axis stretching from Dillingham up through the
Sleetmute area. Precipitation looks to be a rain/snow mix at this
time. However, we will be watching this band closely because if
colder air were to come in a bit earlier, it could be a decent
snow producer. The second area of precipitation will be with the
low center itself. As it makes its way to the YK-Delta coast by
late Sun morning, it will bring another chance for steady snow,
mainly for areas west of Bethel. Colder air will move in with this
feature as well. However, we are thinking it will be somewhat
mitigated by (moderated) flow off the Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Sat and
Sun)...
The Bering will see two significant systems move through during
this time. The first is the current area of low pressure driving a
warm front towards the southwest mainland. The Eastern Bering,
Eastern Aleutians, and Alaska Peninsula will see mostly gale force
southerly winds with this front. There will be a small pocket of
storm force winds south of the chain. Upper level support is
ferrying up some warm air, so we are expecting a healthy amount of
rain as it moves through. The low pressure center itself will
continue to trek to the north and east through the weekend. This
will keep the Eastern Bering fairly unsettled with warm south to
southwest winds and rain showers.

The Western Bering will be rather quiet until a storm force front
arrives late Sun night. Cold air wrapping behind the
aforementioned low will keeps some snow showers and small craft
northerly winds over the zones through most of Sun. By late Sun
evening, expect a dramatic shift to easterly winds over the
Western Aleutians. These winds will increase to storm force by
early Mon morning as the front arrives. Precipitation will start
as snow, but quickly turn over to rain.

&&

.MARINE (Days 3 through 5)...
The models have come into good agreement with the low near the
western Aleutians Sunday night into Monday resulting in high
confidence in the area seeing storm force winds. Confidence lowers
on Tuesday as the models diverge with the track of the low, but
there is agreement that the wind speed will weaken. The models are
also struggling out east in the Gulf with a low tracking into the
area from the south on Monday. Some of the guidance is looking at
gale force winds through much of the marine areas in and around
the Gulf on Monday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast is plagued by model uncertainty resulting
in a forecast leaning towards the ensemble means. The area of
highest confidence is with a storm force low approaching the
western Aleutians Sunday night into Monday. There is also decent
confidence in ridging over the panhandle holding over the area
into mid week with multiple lows tracking through the area to the
west of the ridging. The models are struggling with the timing
and intensity of these lows resulting in the ensembles being
preferred. This setup will likely result in more above average
temperatures for most locations in the southern mainland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...150, 160, 165, 170, 171, 172, 174, 176, 180, 181, 414
         Storms...155
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
MARINE/LONG TERM...DK