Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 241352
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
552 AM AKDT MON OCT 24 2016
.SHORT TERM...Satellite imagery this morning showing a weakening
low in the SE gulf tracking to the west and dissipating. A 970 mb
low in the N Pacific to the west of Washington state will begin to
track northward moving just south of Haida Gwaii through early
Tuesday. An inverted trough from this low will extend north over
the panhandle. Area of high pressure over the Yukon will remain
through Tueday with a high pressure ridge over the central gulf
shifting east. At mid levels a closed low will drop down from the
Yukon and into the eastern gulf through early Tuesday.
Shower bands rotating around the current gulf low will pull to the
west and dissipate through the early morning. Dry weather will
develop through the day and into the night. Variable cloudiness
this morning with sunny skies developing through the day.
Southern panhandle cloud cover will increase late tonight as the
next low moves northward. Fog has been tricky this morning due to the
timing of clearing skies with optimal dew point depressions.
While overnight radiational cooling tonight would favor fog
development think the drying trend through the day along with
increasing winds will limit any fog.
Main issue for the short term is windy conditions. Over the AK
gulf small craft to gale force outflow winds, mainly over the
central and northeast gulf will increase through the day. Pressure
gradient between the Yukon high and panhandle inverted trough will
increase northern inner channel winds to max gales by the
afternoon with max small craft winds over the northern portions of
the central inner channels. Skagway wind gusts will pick up to 40
mph due to the pressure gradient. Easterly outflow gusts will be
more of a concern as cross barrier flow increases. Expect mountain
wave development for Downtown Juneau and South Douglas this
evening and into Tuesday so have upgraded the High Wind Watch to a
Warning. The gradient will produce easterly winds upwards of 65 kt
at 925 mb for cross barrier flow component. The 500 mb low
dropping in from the Yukon for critical level moving in wind flow
reversal and speed change at 500 mb. Temperature inversion was
somewhat in question but NAM sounding showing strong inversion at
850 mb and hires model cross section showing wave in potential
temperature over Salisbury ridge line. Not a perfect Taku wind set
up as the air mass over W Canada is not an ideal cold temp. Went
with Taku gusts of 60 mph.
Used mostly high res NAM models: ARW, NMM, DNG5 to update some
local effects in the forecast grids. Any changes were small.
Some uncertainty with magnitude of winds over the northern inner
channels as some MOS guidance was producing storm force winds, but
pressure gradient and high res models were still in gale force
.LONG TERM...High wind event that begins in the short term
forecast period will last through at least Tuesday morning, as
will strong wind gusts in Skagway. Relaxation of the strong
north-northeasterly pressure gradient will come as a result of the
low to the south beginning to track west into the central gulf as
well as high pressure over the yukon weakening. By Thursday, small
craft winds on the inside are expected to be over.
Next significant threat of precipitation does not come until late
in the week when a frontal boundary to the west interacts with a
low tracking north along 130w. The low itself is expected to
become absorbed into a stronger system to the west. Frontal
boundary become very complicated with at least three separate
boundaries being depicted in to models over the eastern gulf and
southeast Alaska by Thursday afternoon.
Used a blend of NAM and the Canadian NH for updates to pressure Wednesday
/ Wednesday night. Used the Canadian as a foundation for winds.
Blended NAM12 and GFS22 for PoP and QPF for the same time frame.
Temps adjusted primarily with GFS and Ensemble GFS MOS through
Saturday with changes of three degrees or less. Overall forecast
confidence is average.
PUBLIC...High Wind Warning from midnight tonight to 4 PM AKDT Tuesday for
STRONG WIND from 10 AM AKDT this morning through Tuesday
afternoon for AKZ018.
MARINE...Gale Warning for PKZ012-013-051.
Small Craft Advisory for PKZ011-021-022-031>033-041>043.
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