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FXAK67 PAJK 291332

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKDT MON AUG 29 2016

.SHORT TERM...Low pressure west of Dixon Entrance and Haida Gwaii
will continue to be the main weather feature through the short
term period. Bands of showers wrapping around the low have been
moderate to heavy at times across the southern inner channels and
POW Island overnight. This enhancement has been due to a band of
vorticity that will progress northward through the day. As a
result showers are expected to reach the Juneau area in the late
afternoon then continue north through the evening. The band will
weaken as it moves away from the parent low, so have limited
showers across the north/central panhandle to scattered with lower
QPF amounts than the southern panhandle will see. The biggest
limiting factor for the showers over the northern half of the
panhandle is the offshore flow created by the low to the south and
the northerly outflow winds. Yakutat will remain dry for these
reasons, although will have increasing clouds as the vorticity
band approaches tonight.

Winds are one of the bigger challenges for this forecast package.
Tight pressure packing with higher pressure over the Yukon and the
low to the south is causing some outflow winds. In the wintertime
these would be fairly strong due to the cold airmass accelerating
through the passes, however this time of year the winds are
weaker, but how much weaker is the question. Winds at Eldred Rock
increased to sustained 28kt this morning but reliable observations
where the interior passes are, are limited (villages and airports
tend to be built in wind sheltered locations just for that
reason). So some uncertainty there, but did incorporate some
satellite derived winds and velocity data from the radar into the
wind field.

Locations that have some downslope winds, i.e. Downtown
Juneau/Douglas and Skagway, once again remained in the 60s
overnight. Increased the temperatures today and tonight based on
the pattern not changing, but may have not gone warm enough
tonight. Sunny breaks in the clouds today should be fewer than
yesterday with the band moving through...but the northern inner
channels should still be able reach the mid to upper 60s and
around 70 for Yakutat. These are well above the normal of 60F. The
record for Yakutat today is 72, so could be a 3rd day in a row
with a record breaking high! Due to more persistent clouds and
numerous showers the southern panhandle will likely remain in the
low 60s.

Used mainly the NAM12 and available hi-res models for this
forecast package, followed by adjustments for local effects and
current conditions. Forecast confidence is average, but slightly
lower on how many showers will actually make it north of Icy

.LONG TERM...An upper low currently positioned WSW of Haida Gwaii
is forecast to persist through Wednesday night before ejecting
eastward during Thursday. In the meantime, numerous midlevel
impulses will rotate north and west around the upper low, which
will aid in isolated/scattered shower development over the
panhandle during the first half of the work week.

In addition, the combination of surface low pressure over the
northeastern Pacific and high pressure over northwest Canada will
yield a tight offshore directed pressure gradient. This will
favor strong northerlies over Lynn Canal (currently forecast to
peak at 30 kt Tuesday/Tuesday night). In addition, gusty winds
will be possible for Haines, Skagway, and Downtown Juneau through

Friday will be a transition day across the region as the
previously mentioned upper low departs downstream, and a midlevel
ridge shifts east across the gulf and panhandle. WSW flow aloft
then develops across the area Saturday and Sunday, with episodes
of rain subsequently occurring during the remainder of the long
term period.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ012-013-022-036-041>043-051.



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