Small Craft Advisory 714, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
254 PM AKST Thu Nov 17 2016

.SHORT TERM...A low rests well to our south while high pressure
covers Canada. A tighter gradient roughly traces the border with
Canada from the Wrangell-St. Elias to the Coast Mountains. As a
result, Southeast continues under an offshore flow regime. A weak
trough dropping south across our area and stalling tonight over
the central Panhandle was thought to be enough to spark both a
mountain wave event into Downtown Juneau and a period of strong
gustiness through Skagway today. Neither has happened to the
extent we guessed...although we have to say the winds near
Downtown Juneau have been the stronger of the two regimes. Where
channeled flow is most efficient--through the Inside Channels
where the great masters of friction, trees and terrain, stand off
to the side like wallflowers--we have small craft winds racing
southward. Gusts are probably highest out of Taku Inlet where
somewhat sheltered Point Bishop has been a persistent 30 kt. Cross
Sound 25 kt easterly outflow winds seem reasonable through the
period as gradients will change little through Friday afternoon.
Because of our failure to reach gusts to 40 mph or more today in
Juneau and Skagway, we have lightened our winds to something less
threatening through Friday.

While some wind besets the north, most all of the Panhandle has
experienced cool November sunshine today. The only exceptions have
been some upslope cloudiness crossing White Pass into Skagway and
a few clouds that have sneaked into Hyder from an easterly wave.
An isolated or scattered rain/snow shower may pass through the far
south tonight into tomorrow, but impacts will be minimal and any
precipitation very light.

Temperatures will be on the whole two or three degrees cooler
across northern Southeast tonight into Friday while those in the
south will largely be on par with today and this morning with the
possibility of clouds spreading northward. Thus lows tonight over
the south will range from near freezing for the far south and
eastern gulf Coast. While from Petersburg north we should see
widespread 20s with teens possible in the Mendenhall Valley, the
Haines Highway and potentially Gustavus/Yakutat. Tomorrow, highs
will struggle to exceed freezing point across the north, while the
south will climb to around 40. As the atmosphere has been drying
for a couple of days now, we expect no fog tonight.

Confidence is average. NAM and persistence were used for any
changes to the forecast.

.LONG TERM...Dry, cold temperatures and windy conditions will
prevail through the weekend. Actually, temperatures are near
normal for this time of the year, providing testimony to how warm
conditions have been for the first half of November. This pattern
is forecast to change early next week, when a large and fairly
deep low enters the gulf from the west. The associated front will
advect in a warmer airmass and bring the next significant
precipitation to southeast Alaska. With cold low level air spread
out across most of the panhandle, there is a good chance that some
locations will see their second significant snow of the season.
Typically, as overrunning events usually progress, the cold near
surface airmass will get scoured out by a warmer airmass, and what
precipitation remains will transition to rain. This is not so much
what is presently in the long range forecast, as this event is
still several days away. Rather, this aspect of the forecast is
based on the nature of past events. As in the past, snow will hold
out longest over the far northern inner channels. Still too far
off to say how much snow to expect, but confidence is increasing
in this developing overrunning snow event.

Updated Saturday night through Sunday night with GFS in
coordination with WFO Anchorage. Some changes to PoP and QPF early
on using SREF and NAMDNG5. Decided not to go with the very bold
ECMWF for PoP and QPF for the front on Monday/Tuesday. Instead,
blended in the NEW WPC with existing grids, so expect these
numbers to change as the event draws closer and forecasting
methodology transitions to a more deterministic solution and
sharper PoP gradients and better temporal resolution on snowfall.
Remainder of the long range forecast unchanged. Overall forecast
confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ012.
     Small Craft Advisory for PKZ013-022-031-032-052.
&&

JWA/Fritsch

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