Small Craft Advisory 812, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
418 PM AKDT SAT OCT 15 2016

.ANALYSIS AND UPPER LEVELS...
A very amplified pattern exists over Alaska and the Bering Sea.
There is an upper level ridge centered over the Chukchi Sea that
covers the eastern Bering Sea and western Alaska. There is an
upper low centered over the Yukon Territory with the trough
digging into south central Alaska and the northern Gulf of Alaska.
Northerly flow exists between these two features, that is anti-
cyclonic over southwest Alaska and cyclonic over south central and
the gulf. There is a weak trough that stretches across the
Aleutians with the jet stream racing across the Pacific to the
south.

&&

.MODEL DISCUSSION...
The numerical models are in decent agreement through the short
term portion of the forecast (Monday afternoon). There are still
some differences in how they handle the surface low in the gulf
and its associated moisture/precipitation fields. The forecasts
lean towards the GFS.

&&

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

Offshore winds will be trending upward over the next 24 to 36
hours as an area of low pressure in the Gulf of Alaska is slated
to move toward the northern gulf coast and increase in intensity.
As of this afternoon wind gusts up to 40 mph have already been
observed in the Matanuska Valley. With the increasing pressure
gradient from the developing low in the gulf, higher wind gusts
appear quite likely in the coming days. One ongoing concern with
the winds in the Matanuska Valley relates to a wildfire that
started this morning near Sutton. With gusty winds, low minimum
RH values and low recovery RH values over the next 48 hours will
all continue to provide favorable conditions for fire growth.

Winds throughout Valdez and Thompson Pass will also be on the
rise in the coming day. Winds between 40 and 55 mph are expected
through Thompson Pass while the city of Valdez could see winds
between 30 and 45 mph Sunday and Monday. In addition to these
winds, a nice shot of precipitation will be seen across the
northern gulf coast. Thompson Pass will likely see a couple inches
of snow on Sunday with the potential for some visibility reduction
from blowing snow as strong winds move through the pass. In Valdez,
a mix of rain and snow will be seen with little accumulation
expected at this time. More snow will be seen across the northern
gulf coast and eastern Kenai Peninsula on Monday with the
potential of 3-6 inches in Thompson Pass and 1 to 4 inches in
Valdez.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Gusty offshore flow will continue to increase over the weekend and
into Monday over much of the Southwest mainland, as the pressure
gradient increases between the high centered over the Chukchi Sea
and a deep arctic trough digging over the southern mainland
Alaska. This will keep clear and dry conditions across the region
through Monday, with temperatures steadily decreasing as the
coldest air mass so far this season filters into the region with
the arrival of the trough. The strongest cold air advection will
take place overnight tonight and persist through Monday night, as
much cooler air aloft filters in over the area from the North.
Thus, overnight lows will drop well below freezing area wide for
the next several nights beneath clear skies.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Benign showery conditions will continue across the southern half
of the Bering through Monday, beneath a weakening front over the
central Bering and weak cyclonic flow as a North Pacific trough
passes south of the Aleutians. Meanwhile, high pressure and dry
northerly flow will yield mostly precipitation free conditions
across the eastern and northern Bering, with gusty northerly winds
developing by Sunday as cold air associated with the mainland
trough begins to spread over the region.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long range forecast beginning Tuesday will be a slow
transitioning pattern with a persistence forecast through the end
of the week keeping dry and cool conditions inland and rain
across the area waters. Models have been struggling on the how to
resolve the track and the speed of the low currently diving into
the western Gulf. On Tuesday, this closed off system should start
tracking east; models previously lifted the system on it's
easterly track, but a developing wave moving in from the northwest
coast looks to shunt northerly advancement. The northwest low and
another low from the North Pacific slowly breaks down the upper
ridge center over the Bering Strait through the end of the next
work week. The ECMWF and ensemble mean were used to update the
forecast as it was favored for it's run to run consistency.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KH