Small Craft Advisory 466, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
304 PM AKDT Tue Sep 26 2017

.SHORT TERM...Tonight through Thursday...As of 1500 this
afternoon, current WV satellite imagery shows a weak ridge of high
pressure over western Canada, with the ridge axis stretching east
of the SE Alaskan panhandle. A shortwave is currently lifting
across our northern extent, and another shortwave is beginning to
dig out of the parent trough currently positioned over the western
gulf. A substantial plume of moisture is wrapped in with the flow
around the ridge and is being aimed directly at the panhandle,
giving us our atmospheric river event. This onshore flow is
contributing to some substantial accumulation amounts already
across the panhandle, with more expected on the way through
Thursday.

Winds have also been very strong across the area, and we'll
expect winds to remain relatively strong, especially along the
offshore waters where sustained wind speeds may float around 35
knots. This is due to a tight pressure gradient and an additional
weather front that will push through the panhandle late tonight
into Wednesday.

For Thursday, PoPs should begin to diminish throughout the day as
a weak ridge starts to build back into the eastern gulf and the
flow becomes more offshore. Winds should also lighten up once the
pressure gradient weakens.

Generally, the forecast has been pretty consistent, so it didn't
require much change. Any adjustments that were made we tended to
use a combination of the ECMWF and the GFS, as there has been very
good agreement between the two.

.LONG TERM.../Thu night through Tue/ A lot of differences with
models and their ensembles for the weekend and early next week.
Many operational models show a low level ridge over the gulf while
the ensemble means (and latest WPC) have a low. Spread is large
in the ensembles and there has been little run to run consistency.
Given that background, opted to leave current forecast as is.

For Thu night and Fri, cold front should slowly move E of the
area and rain should become showers. Cooler air should move in for
the weekend it appears, but the model differences make for a
difficult temp forecast especially the min temps over the weekend.
All in all, confidence in longer range forecast is very low at
this point.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ041>043-051.
     Small Craft Advisory for PKZ012-022-031>033-036-052-053.

&&

Voveris/RWT

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