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FXAK67 PAJK 182304

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
304 PM AKDT Wed Oct 18 2017

.SHORT TERM...Tonight through Friday...As of 1430 this afternoon,
a broad trough with an embedded shortwave has positioned itself
over the gulf, with the shortwave beginning to lift out of the
eastern gulf. This system has produced heavier cells with a decent
amount of lightning over the gulf and near Haida Gwaii throughout
the day, sometimes popping up along the panhandle this morning. A
dry slot associated with a strong jet aloft, which we can see on
WV satellite, has increased instability in the upper levels,
encouraging development with these cells. There is still a
possibility of some thunderstorms over the eastern gulf waters
along the panhandle through this evening, as cold air with the
circulation remains aloft over relatively warm ocean waters. We
can also still see what appears to be a CU field over the water
on visible satellite.

As this shortwave continues to lift northeast, we expect the
winds to increase at the northwestern head of the associated
surface low. Gale force winds will be possible along the western
edge of the offshore waters late tonight before this surface low
weakens tomorrow. Small Craft Advisory level winds will also be a
concern for the eastern gulf marine zones tonight and continue
for Northern Lynn Canal tomorrow. An additional weak surface low
will develop over the northern gulf near the Yakutat Bay area late
Thursday into Friday morning before quickly dissipating and
exiting the area. A weak ridge of high pressure is then expected
to develop over the eastern gulf Saturday before another shortwave
develops over the western gulf.

Models are generally in good agreement up until Friday regarding
the set up of surface level features for our area. On Saturday,
the model spread increases for the shortwave that begins to
develop over the western gulf during the day.

.LONG TERM.../Friday through Tuesday/Minor changes were made to
longer range forecast. Models are generally good agreement on the
large scale features but have important differences on smaller
scale features and tracks of surface low pressure systems. For
Friday showers will remain over the area as the main upper trof
moves east. The showers will begin to diminish some with more
upper and mid level ridging ahead of the large system moving out
of the North Pacific.

The system of concern in long range is a complex low expected to
move into the gulf by the weekend as mentioned above. Models are
getting in better agreement with a deep 960s low moving into the
gulf but there are still differences in the details. This low will
spread strong gales from the Southeast over the gulf along with
large sea heights of 20ft. Over the inner channels the winds over
the northern half may be out of the north from 15 to 20kt with
the southern half seeing southerlies to near 25kt due to the
track of the main surface low. Temps will be an issue with some
cooler air moving in with the north surface winds and a threat for
snow but that threat will remain over the far northern inner
channels and along the Klondike and Haines highways. For the most
part the forecast is a wet one with good onshore flow over the
weekend and into next week.

Later next week, there is a lot of uncertainty with any track and
continued to use WPC from Monday into Tuesday. We will need to
monitor a system that could have the remnants of tropical cyclone
Lan embedded with it on Monday or Tuesday. The GFS is faster and
further to the west with this while the EC and GEM are slower and
further to the southeast.

In the mid term used a mix of the 00zEC and 00zNAM with about
average forecaster confidence.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ012-022-034-036-041-043-051.
     Small Craft Advisory due to Seas for PKZ042-052-053.




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