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FXAK67 PAJK 292256
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
256 PM AKDT FRI JUL 29 2016

.SHORT TERM...Weakening low over the eastern gulf will dissipate
as it moves into the central panhandle tonight. A shortwave trof
aloft over the southern Yukon will move south through the eastern
inner channels tonight. Deep layer ridge will move into the
eastern gulf late tonight and remain Sat...with a weak shortwave
trof moving through the top of the ridge across the northeast gulf
coast during Sat. Used blend of the 12z GFS/ECMWF/NAM for the
pressures and winds. Used 12z NAMDNG and 09z SREF with some
manual edits for POPs.

Main forecast concerns will be precip potential...winds...and
chances for drizzle and/or fog. There are some showers over much
of the area attm with the least amount of shower activity over the
north. Showers should diminish along the outer coast tonight...but
the more eastern inner channels will see some showers with
shortwave dropping southward through the area tonight. The
southeastern inner channels may see some showers into Sat but
should see diminishing trend. Finally...some showers may develop
as weak shortwave moves across the far north gulf toward Yakutat
Sat.

As for winds...strongest winds will generally be south of the low
and on front side of surface ridge over the southern gulf....with
20-25 KT expected tonight. Those winds will gradually weaken as
low dissipates tonight. As surface ridge becomes better
established over the eastern gulf Sat...there will be some
enhanced flow along the outer coast with tip jets becoming likely
near Cape Spencer and Cape Decision by afternoon. These could
reach 20 to 25 KT by late afternoon. Another area where 20 KT or
more is likely is Lynn Canal. They will have 20-25 KT south winds
diminish tonight...then develop again Sat afternoon with some
thermal enhancement.

As ridge aloft helps dry out mid levels tonight...and with low
levels remaining moist...think some drizzle will develop along the
central outer coast and as far inland as Gustavus by late tonight.
This drizzle should diminish by late Sat morning as daytime
heating helps mix in some drier air to lower levels. Think there
will be patchy fog over the central inner channels tonight with
some breaks in clouds developing...with some fog forming in the
drizzle along the outer coast.

.LONG TERM...The ridge axis stalls over Southeast Alaska Saturday
night into Monday morning before it is pushed into western Canada
by a low forming over Southwest Alaska Sunday. Warm air advection
occurs over the Panhandle increasing stability aloft despite weak
onshore flow in the low levels. Thus, just as for late tonight
into Saturday morning, we speculate that occasional drizzle will
fall along the coast Saturday night and Sunday morning as well as
Monday night. After studying model soundings for the same period,
we elected to remove the isolated to scattered showers for much of
the Panhandle and replace with drizzle confined to the coast. We
did leave the isolated shower activity for Yakutat, but confidence
is falling that there will be enough instability here to garner
anything other than drizzle or sprinkles. We can sum up the mid-
range of Saturday night into Monday night to be mainly dry for
Southeast Alaska. In addition, weak onshore flow on Sunday will
veer northwest by Monday thereby allowing more sun to over
Southeast. To compensate we warmed temperatures on Monday
Panhandle-wide and for Tuesday over the south as clouds build from
the west as the low over the western gulf approaches.

This low then moves into the central and eastern Gulf mid-week to
spread chances of rain into the Panhandle late Tuesday into
Thursday. The best chance of rain for the north will be Tuesday
night into Wednesday while the south receives the best chance
Wednesday into Thursday. Temperatures will respond by dipping back
into the lower 60s during this time with the potential for it to
be cooler should we determine where rain will actually fall.
Currently, we cannot say where exactly rain is likely as model
spread still exists regarding both the system`s progress and its
arrival time. Beyond its passage late in the week, ridging once
again rebuilds behind it and thus temperatures rise and rain
chances decrease.

Only minor tweaks for local effects were made to winds in the
mid-range. Monday and beyond we used ECMFW, the GFS, and WPC at
various times to slow down the low`s arrival while at the same
time speeding up its departure at the end of the week. Forecast
confidence is average.

&&

.HYDROLOGY...All gauged streams and rivers have fallen below
bankfull levels this afternoon...with Mendenhall Lake the last of
them to do so. Think water levels will continue to drop for the
most part tonight and Sat with precip amounts remaining on the
light side.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012.
     Small Craft Advisory due to Seas for PKZ041-042.
&&

$$

RWT/JWA

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