Small Craft Advisory 666, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
359 PM AKDT Mon Oct 31 2016

.SHORT TERM...Upper low moves in over the Bering Sea with trough
and associated surface front moving into the central gulf. Area
of upper level high pressure remains over the Yukon and western
Canada. The front will track across the AK gulf overnight crossing
into the southern panhandle by Tuesday morning then tracking
northward. Fog was the main issue for today with dense fog near
Angoon, Petersburg, and Kake early in the morning then more fog
developing near Ketchikan and over Clarence Strait in the late
morning. As the nocturnal inversion broke later in the day and
surface temperatures began to warm the fog and low stratus deck
began to clear. With advancing front and increasing cloud cover
do not expect fog to be an issue again tonight.

Precip will begin over the southern regions tonight as showers,
then as the front advances becomes more steady rain. Still some
cold air in place over the north so might see some snow mix in
with rain late tonight, but precip will switch to all rain through
the day as warmer air aloft moves in.

As the occluded front advances and low level jet develops, winds
will increase to gale force over the eastern gulf tonight and
into Tuesday. while the front moves overland it begins to shear
apart with mid level dynamics weakening, so do expect panhandle
and inner channel winds to increase by the morning, but remain at
or below 25 kt.

Early in the forecast period models remain in fair agreement and
have been showing good run to run consistency. Nudged the
forecast using new NAM and NAMDNG which gave bit more definition
to the gulf front with a slight increase in timing of the front
and higher pops over the central and northern panhandle. Overall
changes were small. Forecast confidence is bit above average, with
higher confidence in wind forecast but lower with precip type late
tonight and early Tuesday morning.

.LONG TERM...Potential for some very impactful weather mid week
going into the later half of the week, but confidence is rather
low on details. At issue is an upper level zonal pattern with
numerous strong short wave features developing along the jet.
Model agreement by Wednesday evening extremely poor with solid
gale force lows being depicted by the models in such a way over
the far southeast gulf so as to have profound impacts on where the
wind will be, from what direction, and how strong. Model blending
for Wednesday night not considered practical due to model
differences, so opted to use the GFS as a good middle ground -
significantly stronger than the previous wind forecast, but not as
strong as the 00Z ECMWF. Surface pressure depictions in GFS and
Canadian NH by Thursday morning a little more coherent, so blended
those models for pressure. Resulting wind forecast Thursday
through Thursday night is, once again, significantly stronger
than previous forecast, but not as severe as being depicted by the
Canadian NH. Bottom line thinking on these wind changes was the
desire to be prepared for significant winds and to err on the
cautious side.

In terms of precipitation, similar uncertainty exists here as
well, but potential impacts considered to be much less. Blended
the Canadian, GFS, and existing grids through Friday night.
Blended new WPC to existing grids thereafter.

Overall forecast confidence is below average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ042-043-051-052.
     Small Craft Advisory for PKZ012-013-021-022-036-041.
     Small Craft Advisory due to Seas for PKZ053.
&&

PRB/Fritsch

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