Small Craft Advisory 864, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 AM AKST Sun Nov 4 2018

.ANALYSIS AND UPPER LEVELS...
Infrared Satellite shows high pressure continuing to dominate
over mainland Alaska, while low pressure is moving across the Gulf
of Alaska indicating a more zonal pattern cutting underneath the
ridge. Zonal flow is also apparent in the western Bering Sea. IR
Satellite also shows some low level stratus that has reformed and
is drifting around the Copper River Basin.

Northerly flow at the surface associated with the high pressure
currently in place is producing localized winds in places like
Seward and Whittier. Gusty offshore winds are also occurring in
Thompson Pass and starting to trickle down into Valdez. The low
moving across the Gulf of Alaska is weakening as its goes, just
producing some rain showers that are being observed on the
Middleton Island RADAR.

&&

.MODEL DISCUSSION...
Models continue to be in good agreement through midweek. Run to
run consistency also looks good. This means high confidence and
continuity in the forecast with only minor changes overnight.

&&

.AVIATION...
PANC...VFR conditions and light offshore winds will persist for
the next couple of days.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Upper level high pressure will continue to build over the area
through Monday. Dry and clear weather is expected through Monday
night. Some patchy low clouds and fog are possible over the Copper
River basin with strong a strong low level inversion. Some fog is
also expected through eastern Turnagain Arm. Offshore winds will
increase today as the surface pressure gradient tightens. The
surface gradient will weaken Monday morning through Monday night
as the upper level high settles in over Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today through
Monday Night)...

There are several weather features to note that may produce
localized minor hazards across portions of the area the next
couple days. Going chronologically, the first is a subtle, weak
front that will move into the coast of the Kuskokwim Delta later
this morning and slowly push eastward, reaching Bethel after
sunset. During the brief time the front is in the vicinity, it
will bring in moisture into an atmosphere that will have cold,
sub-freezing air near the surface, and warmer, above freezing air
just above it. That temperature profile supports freezing rain.
The key with this however is that the front will have very
limited moisture to work with, so many areas may not see any
precipitation at all, and for those that do it will be very
light. Thus, a forecast update was made to simply call it
freezing drizzle. Very minor ice accumulations are possible in
areas that see the most persistent freezing drizzle across the
Kuskokwim Delta today into this evening.

In the upper levels, ridging moving across Southwest Alaska
tonight will help support moving warm air over the area aloft and
making the atmosphere very stable. With the lack of wind, and only
partly cloudy skies across the Lower Kuskokwim Valley and Bristol
Bay tonight, areas of fog are likely to develop. Fog was also
included in the Kuskokwim Delta, but it will likely be the result
of the aforementioned front and freezing drizzle. A second,
stronger front is expected to move into the Kuskokwim Delta late
Monday night into Tuesday morning, but warmer air out ahead of it
is expected to keep the precipitation type as mostly rain, which
will remain on the light side.

Another potential hazard for the Monday through Wednesday time
frame is an expected prolonged period of steady south to
southwesterly winds moving into the coast, which may have impacts
as far as high water levels are concerned.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Monday Night)...

The weather across the Bering currently is about as benign as it
gets with no major weather systems impacting the area. However,
that will quickly change later today as a strong front enters the
western Bering, bringing gales to the western Aleutians. As the
front occludes out tonight and weakens, the parent low will swing
in behind the front, leading to widespread gales and even areas of
storm force winds over the far western Bering during the day
Monday. The northerly track of the low should keep the western
Aleutians to just gales during the day. By the time those gales
approach the Kuskokwim Delta Tuesday morning, the low and its
winds should have appreciably weakened, keeping impacts minimal.
The low cause a renewed blast of cold air out of Russia to move
over the Bering for mid-week.

&&

.LONG TERM FORECAST (Days 3 through 7/Monday through Friday)...

Models seem to be in better agreement through Friday next week as
we watch the progression of two lows across the Bering Sea. The
first low pressure system is expected to cross the Bering Sea on
the north side and continue northward through the Bering Strait on
Tuesday and Wednesday. Although this is a slightly different track
than what the models were showing yesterday, for the most part,
impacts along the west coast haven't changed. Ridging over the
mainland is expected to remain in place during this time frame, so
the front associated with this low will move onshore and then
rapidly weaken late Tuesday and into Wednesday morning.

By Thursday, the second low pressure system appears on the horizon
in the western Bering Sea. EC/GFS are showing good consistency on
the storm track through Friday, which lends confidence to the
storm moving through the central Bering and possibly bringing
winds and waves to the eastern Bering as early as late Thursday
evening. However, by Friday, model solutions begin to diverge. GFS
wants to weaken the storm and push it northward through the Bering
Sea, while EC prefers to keep the storm a little stronger and move
it onshore near the Kuskokwim Delta. Where this really makes a
difference is in the Gulf of Alaska. If the GFS pans out, there is
potential for a storm to move up from the south, bringing winds
and precipitation to the Gulf coast late Friday night. If the EC
solution is correct, conditions in the Gulf will remain unsettled
but will not be influenced by a single storm. Consequently, the
long term forecast remains certain for stormy weather in the
Bering Sea, with a storm possible in the Gulf of Alaska by the
end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 411.
Gale Warning 412, 413, 177, 178, 185, 127.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...LF