Small Craft Advisory 949, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 PM AKST Fri Nov 30 2018

.ANALYSIS AND UPPER LEVELS...

Seems the atmosphere is taking a back seat to the local
geomorphology today. Big picture, there is an active weather
pattern developing as a strong upper low over the Bering Sea
shifts eastward. Embedded within it are numerous shortwave
troughs, the first of which is moving toward Nunivak Island. A
second stronger low is quickly moving northeast toward Dutch
harbor and will move inland this evening. A third low is forming
south of Shemya, but is currently not impacting the Bering waters,
however, it will be a weather maker heading toward the end of the
weekend. The first low moving into Southwest now is already
bringing in quite a bit of warm air and mostly rain (with some
interior snow, although will quickly change over to rain). This
front will quickly shift east this evening into Southcentral,
bringing rain and snow to most of the region.

&&

.MODEL DISCUSSION...

The numerical weather models (besides the huge outlier Canadian
Regional) are all in good agreement with the general pattern
heading through Sunday evening. There are some slight
differences, but overall they pain a good picture of what to
expect. Basically, all of Southern Alaska is expecting the passage
of three separate lows, all of which will bring a mix of rain,
snow, wind, and warmer weather to Southern Alaska through Sunday
night.

&&

.AVIATION...
PANC...A challenging TAF for this evening and Saturday as a front
moves into the region. Expecting light snow to develop late this
evening then end by morning. Currently it is expected to be light
with conditions remaining above IFR, but briefly dropping to
periodic MVFR. By late morning Saturday, expecting strong
southeast winds to move into terminal with gusts to 35 MPH, then
dropping pretty quickly through the evening.

&&

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

Our first storm system of interest is an area of low pressure
continuing to life across the eastern Bering Sea. An associated
surface warm front will reach the Kenai Peninsula tonight,
reaching the central Mat-Su Valleys to Copper Basin by late
morning. Widespread snowfall will develop ahead of the front,
before briefly changing over to freezing rain or a rain, snow,
sleet mix as it approaches. One it lifts north of the area, much
drier air will advect into the region at 850 mb, reducing the
precipitation coverage significantly. Additionally with a
southeast wind flow we expect the Turnagain Arm winds to get
cranking, with sustained winds of 30 to 45 mph across the
Anchorage Bowl, and 10 to 20 mph elsewhere. Colder air will move
back into the region with a cold frontal passage Saturday night,
with snow showers possible.

Our attention then turns to the next storm moving into the region
on Sunday, with widespread snowfall developing and a few inches
possible.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2/Friday night
through Sunday)...

Low pressure east of the Pribilofs will continue to track into the
northern Bering overnight. As it does, a warm front now north of
Bethel will swing through the interior. There is plenty of warm
air and southerly winds with this system, so snow had changed over
to rain in most locations with the exception of a few locations
across far interior southwest, such as Aniak and Sleetmute. Colder
air will wrap back around the low tomorrow as it lifts and a cold
front sweeps through. This will change the precipitation type
back over to scattered snow snow showers for the Kuskokwim Delta
south to Dillingham Saturday morning. There will be a brief break
in the action Saturday as a ridge crests over the region. The
next system, however, will lift north into the eastern Bering
Saturday afternoon with another round of gusty southernly winds
and a quick change over of snow to rain for the southwest
mainland.

&&

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

Strong gales and areas of storm-force winds will continue many
areas in the eastern Aleutians. As the low lifts north and a cold
front swings east. A second low will take a similar northward
track across the eastern Aleutians beginning Saturday with gales
and widespread rain from Dutch Harbor to Bristol Bay. Winds relax
and turn more westerly for Saturday night into Sunday as the low
lifts into the northern Bering.

For the the central and west Aleutians, a zonal flow with a low
east of Kamchatka will keep westerly winds steady at about 30
mph. This general pattern for the central and western Aleutians
will be in place through the weekend before the next North Pacific
low sweeps a warm front over the western and central Aleutians
late Sunday.

&&

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

The forecast period commences with a longwave trough across the
Central Bering and portions of the North Pacific with a ridge
axis over the Yukon Territory and the Gulf Of Alaska. Between
these longwave features southwest flow aloft will dominate much of
the mainland. There are numerous shortwaves embedded in the upper
level trough. At the onset of the forecast period, the
Canadian/GFS and ECMWF have a surface low near Dutch Harbor,
another surface low west of St. Matthew Island and a dome of high
pressure east of SE AK. Even at the onset of the forecast period
the global models struggle with the placement of the surface low
although they have these features. As the forecast period
elapses, the model divergence becomes more amplified. Generally
speaking, expecting a progressive and unsettled pattern for the
Bering, the Aleutians and SW AK. However, due to the lack
consistency, this forecast package reflects a blend of models.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WSW 145.
MARINE...Storms 155 172. Gales 130-132 138 150 160 165 170 174
180 352 411 414.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...PS