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FXAK67 PAJK 202307

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
307 PM AKDT Fri Apr 20 2018

.SHORT TERM...A shortwave that developed over Haida Gwaii this
morning has moved over the southern panhandle and will diminish
into this evening. Satellite imagery was showing the trough
becoming negatively tilted (strengthening) about mid-morning.
Some areas such as Ketchikan, Elfin Cove, Annette, Metlakatla, and
Yakutat experienced some on and off showers throughout the day
today and a few brief gusts in Ketchikan.

The northern and central panhandle will remain relatively dry
over the next two days, being under the left exit region of the
jet (some clearing expected but scattered showers in the
afternoon due to daytime heating). There will be breaks in POP,
before increasing to widespread POP`s on Sunday and gale force
winds in the Gulf. Some scattered snow showers will be possible
along the highways and higher elevations. The POP field was
blended with NAM/ECMWF and some GFS/SREF.

Maximum temperatures were decreased with a blend of the GFS to
account for some pockets of CAA. Haines and Skagway will remain
warmer than expected due to some downsloping during the day.
Minimum temperatures were decreased for the tonight period.

Pressures were blended with the NAMnest and GFS to show the
barrier jet coming up sooner. Winds over land were a little
complicated with a few directional changes. Model agreement does
well through about Sunday, but there are some variances to the
strength and timing with the next system coming through.

.LONG TERM.../Sunday through Friday as of 10 pm Thursday/ Upper
trof will generally remain over the gulf of AK and NE PAC through
long term period. A couple of occluded fronts will move into the
area, with first one affecting the area Sun-Mon, and second one
on Tue-Wed. Models are in better agreement on these features, and
are showing stronger systems with both. Used 18z GFS/NAM blend for
Sun, then mainly WPC for Sun night onward.

With the stronger systems during first half of long term,
increased winds associated with both, with the second system
getting a bigger wind boost. First occluded front will likely have
one or more low pressure waves moving N along it as upper trof
takes on a more negative tilt, but models differ on timing of
them, so for now have left that detail out. Still, looks like gale
force winds for the gulf, and possibly over parts of the inner
channels as well. First front will be a slow mover due to flow
aloft becoming more parallel to it, so a more prolonged period of
significant rainfall is likely. With the Tue-Wed front, increased
winds 10+ kt for much of the area, and now have near gale force
winds for the gulf. Models differ on how far SE the front gets
before potentially stalling or falling apart, which would have big
impact on where most significant winds and rainfall will occur.

Late in the period, upper trof remains over the gulf of AK and NE
PAC, but models differ on any additional systems moving through
it after Thu. Still, looks like a wet long range period overall,
which should help to alleviate some of the short and long term
rainfall deficits over SE AK.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ036-052.
     Small Craft Advisory due to Seas for PKZ022-041>043-051-053.




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