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FXAK67 PAJK 191327

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
527 AM AKDT Sun Aug 19 2018

.SHORT TERM...Ridge of high pressure persists over the eastern
gulf for Sunday and then hangs on over the panhandle for Monday.
Mostly sunny and generally light winds with local afternoon sea
breezes Sunday. Temperatures got a slight bump up as the lower
levels are fairly warm. 1 to 2 degrees for the the northern
panhandle and the southern panhandle got another 2 to 4. This may
push a few locales to near record warmth for the day.

A very wet front will move east by early monday with rain to
heavy rain mainly west of Yakutat until later in the day when the
heavier rainfall starts fall at Yakutat. Panhandle should be dry
on Monday, and southern panhandle will still under influence of
the warm ridge, so expect another sunny warm day. Monday looks to
be the warmest over the next few for that region of the panhandle,
have warm the highs to the mid 70s to near 80 degrees.

Tuesday, the frontal band will start moving rain into the
panhandle and some gusty winds will spread toward the Yakutat
area. This is discussed more in the following long term section.

.LONG TERM.../Tuesday through Saturday/...A sharply defined,
negatively tilted upper level trough will be situated over the
western gulf at the start of this long range forecast period. The
trough will rotate north and the trough axis will pass over
Southeast Alaska by Tuesday afternoon. Very strong upper level jet
support and vigorous mid level vorticity will strengthen a weather
front that is forecast to bring heavy rain to the northeast gulf
coast area Tuesday and Tuesday night. Current 24 hour rainfall
total for the northeast gulf coast ranges from 1.65 inches in the
Yakutat area to as much as 3 inches west of Icy Bay. Rain will
spread south and east through the day and night Tuesday, but the front
will weaken rapidly as the parent low weakens over south central
Alaska and the front loses favorable jet support. As the low
weakens and fills and the front moves out of the areas, high
pressure will build in over the gulf from the south on Wednesday.
Models are indicating that a short wave will ride up over the top
of the ridge on Thursday evening, mode agreements on this feature
is currently very poor with GFS being by far the most aggressive
in terms of PoP. For now, have left the forecast for the latter
half of the upcoming week as a very broad brushed high end chance
to low end likely for the probability of rain.

The low associated with the front on Tuesday will be weakening as
it approaches from the southwest. Thus, have only small craft
winds associated with the front over the gulf. residual ridging
over the panhandle should result in very little wind on the
inside at first. Gradient pinching as the filling low tracks
inland and off to the east will result in a stronger southerly
pressure gradient over the far northern inner channels. Small
craft winds are anticipated over lynn Canal Tuesday night through
Wednesday afternoon.

Daytime highs for the week are looking to be seasonable, ranging
from the upper 50s to mid 60s. Overnight lows will trend a few
degrees warmer than normal for late August owing to the expected
cloudiness associate with first the front and then the short wave.

Used a blend of GFS and ECMWF for updates to pressure through
Tuesday night with GFS as the foundation for wind speeds. PoP and
GFS from GFS for the same timeframe. Temperatures adjusted using
GFS and ensemble MOS. Overall forecast confidence is average.


.AVIATION...Patchy morning fog for Yakutat and Klawock with
visibility as low as 1/2 mile at times, and some LIFR low clouds
near Petersburg this morning. Fog and low clouds should lift by
mid morning again, for another nice day of flying. Heavy rain will
start to spread towards Yakutat on Monday and should be moving in
Monday night.


.HYDROLOGY...No concerns for Sunday, however with an Atmospheric
River moving slowly eastward into the Northeast Gulf Coast Monday.
Expected Rainfall is looking to be 3 inches or more for higher
terrain. Expect the rivers to react with all of this new water
flowing into them. The AR will weaken as it shift into the SE
panhandle Tuesday, so the expected rainfall is lower, the rivers
and streams will get a bump too.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ052.
     Small Craft Advisory due to Seas for PKZ041>043-051.




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