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FXAK67 PAJK 202300

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
300 PM AKDT Wed Sep 20 2017

.SYNOPSIS...A surface ridge will shift east across the gulf and
produce fog over the outer coast and inner channels Wednesday
night and Thursday morning. A front will enter the eastern gulf
Thursday night and spread rain across the Panhandle by Friday


.SHORT TERM...Wednesday evening through Thursday night/...Light
winds, a ridge to the west, and low tide near daybreak aided in
the formation of locally dense fog this morning. Persistent light
winds through much of the day allowed patches of fog to linger
over portions of the inner channels into the afternoon. Little
change in the short term forecast issues this afternoon with no
change in airmass, so a return of the fog is expected again
tonight with similar impacts to aviation operations.

When the fog did finally lift, gentle sea breezes set up in the
usual spots over the inner channels and a small craft
northwesterly wind has formed in Cross Sound. These winds will
diminish with sundown and am expecting drainage winds to form late
tonight over the far northern inner channels. An approaching
front has begun to displace the ridge over the far eastern gulf to
the east. The ridge in turn is pressing up against the remains of
an inverted trough and is producing small craft northwesterlies
over the coastal marine zones from Cape Edgecumbe south to the
Dixon Entrance. These winds are expected to relax tomorrow as the
ridge axis moves east.

The front referenced above will push east across the gulf Thursday
and spread rain across the panhandle from north to south and west
to east will all locations in rain by late Thursday night.

Little change in the short term forecast with updates made using
Both NAM and GFS. Temps adjusted using bias corrected MOS and
ECMWF. Overall forecast confidence is above average.

.LONG TERM.../ Friday to Tuesday / Upper level ridge axis will
shift east of the panhandle during the day Friday, and the rest
of the ridge will slowly move eastward to the western CONUS into
western Canada region by the following mid week. Which means any
protection from the rain moving into the western gulf at the end
of the week is ending as well. Once the onshore flow and rains
begin early Friday for southeast Alaska Panhandle, rain is
expected for the remainder of the forecast week.

First front spreads in late Thursday night early Friday with a
good burst of rain. A trailing wave lifting across the central
and southern panhandle is expected late Friday night. Following
that, out of the central pacific, is another developing system at
the head of what may be the start of an atmospheric river aimed
towards Haida Gwaii by Sunday. Significant amounts of rainfall
could be expected for the southern zones Saturday night into
Sunday. The present wind forecast for the event is around 25 kt,
but this could be bumped up if the low continues to develop.

Friday`s forecast was adjusted slightly with influence from the
NAM and ECMWF while the later portions were WPC and some ECMWF.
May see the track on this shift more by Wednesday afternoon if the
new GFS runs are leading the change in pattern, as the gfs
solution may have more of the energy concentrated over the
southeast portion of the gulf.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ022-041-042.




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