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FXAK67 PAJK 261402
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
602 AM AKDT Thu Apr 26 2018

.SHORT TERM.../through Friday night/ A weak occluded front over
the eastern gulf will drift E, and dissipate over the central
panhandle this evening. High pressure ridge will build NE across
the eastern gulf and SE AK tonight and Fri. This ridge will weaken
some as a trof moves across the northern gulf Fri night. Used a
blend of the 06z NAM and 00z GEM to handle the main features.

Main forecast concern is precip potential. The front over the
eastern gulf will have a couple of minor sfc low pressure waves
that ride NE along it today. Strongest upper level shortwave will
move NE across the gulf today, and be into the Yukon by this
evening. Rain will occur along and just ahead of the front, and
will be most concentrated near the weak low pressure waves and
upper shortwave. Have gone with highest POPs across the northern
panhandle today, then a gradual decrease in the precip will occur
tonight as front moves inland and dissipates. The tail end of the
precip could be more like drizzle as shallow low level moisture
remains even after the front dissipates. Then, later Fri into Fri
night, there could be some precip with the weak trof that moves
across the northern gulf. Models differ on how strong the
supporting upper shortwave will be, which will affect how far S
any precip from the trof gets. For now, keeping highest POPs
(chance to likely) over the NE gulf coast Fri afternoon and
night. Do have low POPs into the N panhandle during latter part of
Fri night however as trof and supporting shortwave reaches the
N-central outer coast.

Otherwise, will have plenty of clouds around today, even over the
S, as mid-level cloud band moves through them. Have lowered max
temps a few degrees area wide today, due to precip over the N and
clouds over the S. Do expect more breaks in the clouds to develop
across the far S later in the afternoon, but not enough to reach
the previously forecasted max temps today. Any fog going on early
this morning should dissipate by mid-morning due to thicker
mid-level clouds moving in. Left out fog tonight as lower level
NW flow will be increasing with the ridge building in, but if
enough breaks in the clouds develop where light winds are
occurring, then cannot rule out some fog. The NW flow will
increase further on Fri, with up to 25 KT winds expected over the
far eastern gulf.

.LONG TERM.../Saturday through Thursday/ Upper level pattern goes
through slight pattern change early next week. Relatively zonal
flow over the weekend transitions into a more trough/ridge pattern
by mid next week featuring a ridge over the panhandle and western
Canada with a trough over western Alaska and the Bering Sea.
Generally good agreement on the overall upper level pattern from
the models though confidence becomes average toward mid next week
as trough/ridge axis position varies between models and the
operational GFS is displaying a much sharper, and stronger ridge
axis over the panhandle then any other guidance.

At the surface, a ridge over the gulf and its resulting NW flow
over the panhandle will continue the dry spell for areas east of
Mt Fairweather into the early weekend despite the upper shortwave
moving through at that time (thought some areas of the northern
panhandle may see some showers out of it). West of Mt Fairweather,
enough of the shortwave will survive for at least damp conditions
for the norther gulf coast. Into Sunday and Monday, the surface
ridge becomes flatter as more shortwaves pound into the western
side of it through the weekend. Surface flow becomes more onshore
and overall forecast becomes noticeably wetter especially for the
north Monday into Tuesday as a result. Feature is rather weak
through so not expecting a lot of rain or wind with it.

Forecast confidence begins to falter into Wed and Thu as
differences in how strong the upper ridge building over the
panhandle will be comes into play. The GFS displays a noticeably
stronger ridge that deflects most of the gulf storms toward Cook
Inlet while most of the other guidance displays a weaker and
flatter upper ridge that allows more storm systems into the area.
Current ensemble guidance favors the wetter approach displayed by
the ECMWF and Canadian so the current mid week forecast reflects
this with a generally damp and cloudy forecast. Temperatures
remain near or just below normal for the period.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ042.
     Small Craft Advisory due to Seas for PKZ022-041-043-051>053.

&&

$$

RWT/EAL

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