Small Craft Advisory 915, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 AM AKST Sun Nov 20 2016

.ANALYSIS AND UPPER LEVELS...
The flow pattern aloft looks different, yet still the same this
morning. A baggy weak trough stretches from Kamchatka eastward
thorough the mainland with no real center or organization at all.
The active jet stream extends from east Asia through the northern
Pacific where several disturbances are combining south of the
Alaska Peninsula to re-orient the longwave pattern. A blocking
high pressure sits over the Arctic Ocean leaving much of our
forecast area under weak flow aloft.

The remnants of a dying upper low are moving inland over the
northern Gulf with the main effect being rain/snow showers. A
disorganized front stretches from the Pribilof Islands eastward
leaving a showery regime over the eastern Bering.

&&

.MODEL DISCUSSION...
While in good synoptic agreement, the track and position of a
surface low approaching Kodiak Island are still up for debate with
the EC/GEM further north/east and the NAM/GFS further south and
west. Impacts will be how strong the northerlies get on the back
side of the system around Kodiak Island. The amount of clear sky
has given every model/MOS guidance fits with the low temperatures
lately. Beyond that, the front entering the Bering today is well
agreed upon in timing/strength.

&&

.AVIATION...

PANC...VFR cigs are expected through early afternoon. Cloud bases
lower but are expected to remain VFR from 00z until around 07z
this evening with light snow possible as a warm front crosses the
area from east to west. Ceilings should rise again with frontal
passage after 07z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An area of snow showers is moving inland over the north Gulf
Coast this morning ahead of a warm front moving slowly northward
in the Gulf of Alaska. These snow showers will mix with or turn to
rain as temperatures warm up this afternoon. Kodiak Island will
likely get some snow this morning that turns to rain by the
afternoon with this warm front.

The timing of the front has been a little bit of a challenge as it
is associated with an elongating low which has thrown some doubt
into exactly how fast the front will move and how the low
structure will look as it becomes complex, with multiple centers, over
the next two days. The area of biggest uncertainty with all this
is over and south of the Gulf of Alaska with inland areas not
affected as much with this situation.

&&

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

The offshore pressure gradient will strengthen throughout the day
today which will allow northerly winds of 5 to 15 mph to be common
across much of Southwest Alaska. This will help keep fog at bay
this morning and future mornings as drier air from the interior is
advected southward. Another feature of the offshore flow is that
it will keep any snow chances at bay through at least the first
half of the week as the moisture aloft (especially within the
first several thousand feet above sea-level) diminishes significantly
over the next 24 to 36 hours. Temperatures appear likely to remain
slightly below normal through the forecast period with the
reinforcing shot of cold air from the arctic already evident
based on temperatures across much of the state this morning.

&&

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

The complex weather system yesterday with multiple low centers
across the southern Bering Sea and North Pacific is a thing of
the past. As expected, the low pressure systems have phased into a
single surface low south of the Alaska Peninsula which has been
quite evident on IR imagery and scatterometer data. A nice swath
of gale force winds will be seen near the Central Aleutians
through this afternoon before a weak ridge moves over the southern
Bering Sea. While this weak ridge will bring a brief reprieve of
strong winds and moderate to heavy rain to the Western and Central
Aleutians, an area of low pressure over the Kamchatka Peninsula will
strengthen. This low will push a gale force front across the
western Bering Sea late tonight into Monday morning and will
continue to move eastward into the eastern Bering Sea by Tuesday
morning. Luckily, by the time the low pressure system moves into
the Bering Sea on Tuesday it will have already begun to weaken so
winds in excess of 45 kt are not expected at this time. However,
due to a persistent and dynamic fetch, seas approaching or
possibly exceeding 35 ft will be possible over the western Bering
Sea on Tuesday. A decent moisture anomaly should accompany the
front as it moves into the Bering Sea which will likely produce
another shot of moderate to heavy rainfall across the Bering Sea
and Aleutians yet again.

&&

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

From previous discussion...

The active pattern will continue through next week with multiple
lows moving across the forecast area. However, the storm track
looks to largely stay south of mainland Alaska with lows moving
across the Aleutians and then into the Gulf. This setup will keep
most of the precipitation and warm air out of the mainland with
coastal areas seeing the majority of the precipitation. Although
the models disagree somewhat on the timing of the various lows,
they are in decent agreement with the position of the storm track.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...119 120 130 132 138 139 150 155 165 173-178 185
				 411-413.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
AVIATION...CC
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DK