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FXAK67 PAJK 212245

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
245 PM AKDT Mon Aug 21 2017

.SHORT TERM.../To Thursday morning / Frontal band associated with
the system that tapped into the moisture of Ex Typhoon Banyan has
moved across much of the panhandle but has stalled at line
roughly from Klawock to Petersburg. A second impulse of heavier
precipitation moving northward on the front and is responsible for
holding the front to the west. The front will begin to move east
overnight and Tuesday. Locally gusty winds from a low level jet
tonight into the southern panhandle may bring gusts up to 35 mph
at times.

A cold trough moving into the northeast gulf coast waters and
could have enough instability to spark some T-storms Tuesday and
Tuesday evening. The low aloft has with it a moderate to cold low
core aloft and should track across the gulf and will also
continue trying to start more thunderstorms near the instability
with the low. Tuesday night into Wednesday evening think these
will try to move towards the southeast panhandle. Therefore have
slight chance over the marine waters, but have not tried to spread
them inland to the Prince of Wales area.

Rains over the southern half to third tonight is likely to be
heavy at times increasing the stream flows. See Hydrology section
for further details.

.LONG TERM.../Wednesday through Sunday/ Upper level low in the
southeast gulf will weaken and move to the SE followed by a ridge
building over the gulf and then panhandle. By Thursday another
upper level low tracking E from Kamchatka will drop over the
western AK gulf. Estimate this low center will eventually swing
up to the northeast gulf coast by Saturday with a broad area of
low pressure still covering most of the gulf. Through the weekend
expect a series of waves to rotate around the main low and then
over the panhandle. At the surface a low in the SE gulf on
Wednesday will have potential to produce small craft winds over
the coastal waters before it weakens and moves inland.
Precipitation likely to diminish from N to S as this low moves
into southern British Columbia with some lingering shower
activity. Any dry period will be short lived as the next surface
low moves over the AK peninsula and its associated front crosses
the gulf and then over the panhandle late on Friday. Current
projections have a wet weekend as short waves at the surface
continue to move in bands of rain. In addition to the rain
potential for stronger winds with this low and front, at least
getting up to small craft levels over the gulf coast. Once again
this system showing low fetch of moisture and while GFS IVT
analysis is aiming the heaviest amounts just south of the
panhandle still potential for periods of heavy rain.

Models still in fair agreement for the Wednesday system but did
use a blend of GFS with some NAM in nudge winds up. Later in the
period operational GFS and ECMWF still in good agreement and with
more detail than WPC were used to refresh grids to Friday. For
the rest of the time kept with WPC guidance. Forecast confidence
is bit above average due to model agreement.


.HYDROLOGY...The burst of heavier rains tonight as the moisture
pocket moves through is expected to drop 2 to 5 inches with
higher amounts in the higher terrain. Rivers and streams have been
reacting well to the recent rains, and with nearly all of the 2-5
inches expected to be run off rivers and dams will increase water
levels. Local ponding near communities, seem to be the worst
flood threats expected from the event though the WFO will continue
to monitor the situation if an exceptionally heavy pulse of rain
falls in one of the basis.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ036-041-052.
     Small Craft Advisory due to Seas for PKZ042-043-051.




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