Small Craft Advisory 800, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
331 PM AKST Tue Dec 20 2016

.SHORT TERM...A front is currently moving into the panhandle this
afternoon. Persistent southerly flow and WAA will keep temps in
the mid to upper 30s overnight except for higher elevations and
wind sheltered areas where upper 20s to low 30s expected for
overnight lows. Snow concerns remain limited to the higher
elevations, but could see some snow mixing in with stronger
showers in wind sheltered areas, however, do not expect
any accumulations. Snow accumulations of a couple inches expected
above 500-1000ft along the Klondike Highway and near Hyder. This
front will also bring gusty winds to much of the panhandle this
evening and continue to expect widespread gusts of 40-50 mph.
Winds will rise rapidly over the inner channels with strong to
near gale winds mainly Icy Strait southward. Winds will persist
through the evening before diminishing late as low weakens over
the NE gulf tonight. Numerous lightning strikes detected over the
gulf today and with the cold pool aloft and lapse rates 8-10C/1kft
expect isolated TSTMs to continue over the gulf and outer coast
this evening, so kept mention of TS in forecast. Winds and precip
will ease early Wed as the parent low dissipates, but with
continued deep onshore flow continue to expect precip across SE
through Wed. Current forecast a little quick in bringing winds
into southern panhandle early this afternoon, so pushed back the
timing of increased winds by a few hours. Models in good agreement
on synoptic scale through the period, so mainly focused on
mesoscale features and local effects.

.LONG TERM...Transition from the warm wet active weather pattern
to a colder drier pattern for the weekend, then back to a another
wet pattern with increasing temperatures for next week. Complex
surface low in the AK gulf will begin to drop to the southeast
through the end of the week. Uncertainty regarding a wave
development south of the main circulation on Thursday which is
being picked up by the GFS22, somewhat by the ECMWF but only as a
extended trough in NAM and Canadian models. Mostly these model
differences will impact winds over the gulf and may decrease
precip over the northern panhandle faster. High pressure ridge
builds over the AK gulf with inverted trough over the panhandle
and a cold high pressure air mass develops over the Yukon starting
Friday and lasting into Sunday. Winds will shift to the north and
drier cold air will drop in from the north. The broad areas of
higher southerly winds drop off and as northerly gradient
increase will have more localized areas of higher winds in
channeled terrain. For now now expecting, but not ruling out
either, temps to reach the frigid single digits seen previously,
but at least get lows into the 20s to possible teens. with damp
ground, and clearing skies included mention of fog for Friday
night with possible wide spread fog event, but temps could drop
enough to limit any development. Next low and frontal system
approach the panhandle from the west Sunday night and into
Monday. Better change of snow accumulation from the system before
a warming trend depending on how much the cold air becomes
established.

Large model spread early on, but with better agreement decided to
use 12z NAM/Canadian to refresh forecast. Continued the trend to
drop temps for the weekend and lower pops. Forecast confidence is
average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until midnight AKST tonight for AKZ025-026-028.
     Strong Wind until midnight AKST tonight for AKZ023-027.
     Strong Wind until 9 PM AKST this evening for AKZ022-024.
MARINE...Gale Warning for PKZ031-033-034-036-041-042.
     Small Craft Advisory for PKZ011>013-021-022-032-035-043-051.
     Small Craft Advisory due to Seas for PKZ052-053.
&&

BC/PRB

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