Small Craft Advisory 16, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 AM AKST Sat Jan 5 2019

.ANALYSIS AND UPPER LEVELS...
There is a deep surface low northwest of Adak with an occluded
front extending from it. And there is a triple point low that has
formed south of Nikolski. In the latest ASCAT/advanced
scatterometer pass there is a large area of high pressure at the
surface from the Gulf Of Alaska to south of the AKPEN. There is a
fierce jet core south of the chain and the longwave pattern is
becoming more amplified. The radars at King Salmon, Middleton
Island and Kenai are all clear. There does appear to be one shower
on the Bethel radar but it isn't anything impressive. On the GOES
Nighttime Microphysics and the AVHRR (which are both satellite
products) fog and low clouds have been detected again over
portions of Knik Arm, Turnagain Arm and in the Anchorage Metro
area. The coldest area for the southern tier of Alaska remains the
Copper River Basin where temperatures are handily into negative
territory.

&&

.MODEL DISCUSSION...
Models continue to remain in sync with the synoptic features
through the short-term forecast period. Overall, forecast
confidence remains above normal for the Bering/Aleutians and SW
AK. The only fly in the ointment remains the fog issues over
Southcentral Alaska.

&&

.AVIATION...
PANC...Looking at Southcentral Alaska, specialized satellite
imagery has detected several areas of fog and low clouds over
portions of the Anchorage Bowl and the Kenai Peninsula. Compared
to 24 hrs ago, the fog bank is smaller. Looking at the metars the
bases of these clouds are under 500 feet in some places. More fog
and LIFR conditions are possible this morning for PANC. The
boundary layer is generally stagnate based on the light winds and
the presence of an inversion on the skew-t for Anchorage. There
are discernible breaks in the clouds and fog but it difficult to
pinpoint when VFR conditions will materialize over PANC. The
situation is actively being monitored and amendments will be made
when necessary.

&&

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

The overall pattern over Southcentral is similar to yesterday with
a weak upper level ridge over the area and a weak surface trough
in the northern Gulf of Alaska. A weak short wave is washing out
as it crosses over the upper level ridge and bringing in a few
higher clouds to the Cook Inlet region and Susitna Valley. This is
helping to diminish the extent of the fog around Cook Inlet
though patchy fog is likely to move in and out throughout the day.
The Copper River Basin will likely remain with some fog/low
stratus in the lower elevations as there is just not much mixing
of the air to dissipate it. A difference from yesterday is that
instead of significant fog in the Glennallen area with lows in the
single-digits below zero, the fog has lifted to a stratus ceiling
and temperatures have plunged to more than 20 below zero. This is
indicating that there is a chance the stratus diminishes and
clears out today, however think it is more likely to wait until
tomorrow so forecast reflects that.

Outflow winds along the north Gulf coast will persist through the
weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Saturday
through Monday)...
A low level stratus deck currently sits over southwest Alaska,
along with some fog and light snow showers. This stratus deck is
the result of a cold air intrusion from the north, whose flow is
clearly depicted on satellite. These conditions are expected to
persist today as there are no real kickers to change the pattern.
What will be the kicker comes in tonight through tomorrow in the
form of the frontal system currently moving across the Aleutian
Islands. When it reaches southwest Alaska, it will bring a shift
in the wind direction and a band of precip that should dispatch
the stratus deck in place. After this front moves through, there
will be some brief clearing in the weather before the next front
moves in late Monday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Saturday through Monday)...

Two large low pressures systems with storm force winds will work
their way through the Bering Sea and Aleutian Island chain the
next couple of days. The first storm is currently moving through
the Western Aleutians, with an elongated front that is well
removed from the low center. This front moving through the
Central and Eastern Aleutians today and will produce snow/rain and
gusty winds. The storm force winds with this system are more
associated with the low center and in the Western Aleutians and
Central Bering.

Tomorrow into tomorrow night the next low will move north across
the western edge of the Aleutians. A band of storm force winds
will push through the western Aleutians in association with
frontal system with this low, which is a bit different than the
low currently moving through the area. It will also bring a strong
band of precipitation with it. After this low pushes through the
region, the Bering and Aleutian Island Chain will be quiet for the
remainder of the short term.

&&

.MARINE (Days 3 through 5)...

Monday evening, the Bering Sea will be "quieting down" behind a
two strong storm force lows. The remnants of the last storm force
low will be moving into the Bering Strait. This period of time
from Monday night through Wednesday will be characterized by very
broad low pressure with a couple of weak fronts moving in from the
North Pacific. At this juncture, these lows look rather weak and
will likely remain below gale force.

The next front of interest comes late Wednesday night as it moves
north into the western Bering Sea and east toward the Central
Aleutians. This front will likely support strong gales to low end
storm force winds.

Over the Gulf waters, a weak front will move onto the North Gulf
Coast Monday night, but winds will continue to remain below gale
force as the storm track remains well south of the area.

&&

.LONG TERM FORECAST (Days 3 through 7)...An Arctic high over
northern AK and Canada will continue to bring cold dry conditions
and offshore flow to Southcentral and Southwest AK through mid to
late next week. Monday into Wednesday, several shortwaves will
rotate around a low situated over the Bering Sea, bringing periods
of precipitation and increased winds to the Aleutians. These
waves will push weakening fronts toward the mainland resulting in
onshore flow and potential precipitation over the AKPEN, Bristol
Bay, and Y-K Delta areas. Southcentral will remain mostly dry
during this time period, as any approaching boundary will
dissipate by the time it reaches the Alaska Range. Late Wednesday
into Thursday, a potent low from the southwest will approach the
western Aleutians. Models have been fairly consistent with the
basic pattern, but there's uncertainty as to how strong winds will
get in the Aleutians...the low is expected to rapidly deepen with
potential storm force winds, however a slight southerly shift in
its track would indicate primarily gales for the Aleutians. On
that note, models continue to point to the potential for wetter
conditions in Southcentral late next week, but this will be
contingent on the progression of the low upstream.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 185 181 160. Gale 414 165 170 171
172 173 174 179 181. Storm 411 412 413 175 176 177 178 185.

&&

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