Storm Warning 46, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
146 PM AKDT Sat Nov 5 2016

.SYNOPSIS...Major upper low center near 50N 160W with -28C at 500
HPa but the main cold air aloft is over PAKN around -36C which is
truly winter. 250 HPa analysis shows quite the jetsteam across
the Pacific to add a lot of energy for development at the end of
the short term period. A mondo storm went ashore near Cape Spencer
last night after blasting SE with lots of wind and lightning. That
system has since died in the Yukon someplace.

&&

.SHORT TERM...look for some minor ridging inland tonight which
pretty well sets up calm wind and lots of fog. There might be a
few light showers in the evening, but the big emphasis will be fog
that scours out later Sunday morning. Not to steal the thunder
from the Long-Term (pun intended) but there will be a nasty system
come up from the SSW as per a model blend of the 05/12 NAM and
ECMWF. Got some gale force already later on Sunday.

.LONG TERM...A 120+ kt upper jet is forecast to round through the
base of a trough extending south from interior AK across the WRN
Gulf during Sunday night. Model guidance shows the exit region of
the jet spreading toward Haida Gwaii, with strong upper-level
divergence developing over the SERN Gulf. This may yield the
occurrence of a sub-synoptic scale low (as depicted by the ECMWF) along
a front that will be in the process of pivoting NNW across the ERN
Gulf. If this subsidiary low develops, then ESELY hurricane force
winds may become embedded within a broader zone of storm force
winds. The NAM and GFS have trended away from that scenario at
this time, thus have left sustained speeds over portions of marine
zones 41-42 and 310 in the 45-60 kt range. In addition, a tight
E-W oriented surface pressure gradient will favor gusts near 60
mph over AKZ027, which are expected to develop Sunday evening and
last into part of Monday morning. This supports the continuation
of the high wind watch inherited from the midnight shift. For
AKZ028, the ELY component to low-level flow is forecast to produce
wind gusts below high wind criteria...thus the high wind watch was
dropped.

Strong destabilization is forecast to occur in the wake of the
previously mentioned front, as 500 mb temperatures from -26 to -28
C spread ENE across the gulf. This will support a slight chance of
thunderstorms that could persist through mid week. Otherwise,
large-scale troughing will continue over the gulf during the
remainder of the long term period, which will favor additional wet
and windy weather. The next in a series of surface cyclones will
impact the region WED and THU as a strong upper jet spreads NE
toward the panhandle, with a gale to possibly storm force occluded
front affecting the ERN gulf.

&&

.AVIATION...IFR in fog will be widespread a few hours after
sunset. There is so much moisture plus breaks in the clouds and calm
wind that makes fog certain. Guessing breakout 18Z-ish Sunday but
stay tuned for better timing as we see how thick it gets.

&&

.MARINE...Outside there is an awful sea but laying down slowly.
Buoy 46084 is 15 FT at this writing. Inside calm wind and lots of
fog tonight into Sunday. Get ready for the next storm Sunday
night.

&&

.HYDROLOGY...All rivers and streams in good shape in spite some
recent rains that could not overcome the freezing levels and our
dry October.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch from Sunday evening through late Sunday night
     for AKZ027.
MARINE...Gale Warning for PKZ041-042.
     Small Craft Advisory for PKZ021-022-036-043-051-052.
     Small Craft Advisory due to Seas for PKZ053.
&&

JC/Garner

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