Small Craft Advisory 29, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
315 PM AKST Tue Jan 9 2018

.SHORT TERM...Cold upper trough continues to slowly dig southward
across the Panhandle. Associated arctic boundary currently draped
roughly along Icy Strait. These features will drift south through
the evening and overnight hours and linger over the southern
Panhandle on Wednesday before the upper trough shears out to the
east Wednesday evening. A series of fronts spinning around the
main cyclonic gyre over the western Aleutians will not make very
much headway eastward through Thursday as mid and upper level
ridging remains in place over the eastern Gulf.

Dynamic lift from the upper trough and mid level shortwave have
combined low level convergence and frontogenesis along the arctic
boundary to produce periodic snow showers today. Yakutat reported
5.2 inches of snowfall with this boundary last night, and with
the boundary expected to move slowly near the central Panhandle
this evening, think it prudent to continue the Winter Weather
Advisory for the Pelican/Sitka areas. These areas have the best
potential to see accumulations in the 3 to 5 inch range. Snow will
gradually taper off by early Wednesday.

Strong northerly outflow winds will continue behind the trough
this evening and tonight. Northerly winds to storm force over
northern Lynn Canal with strong gales through many of the other
northern channels, especially near interior passes. Temperatures
have fallen through the day across the northern Panhandle with the
strong CAA, and this trend will continue through early Wednesday.
With temps in the single digits to below zero teens over higher
elevations of the Klondike Highway, along with expected winds,
have elected to extend the Wind Chill Advisory through early
Thursday. Wednesday night will be one of the coldest nights of the
season over the northern Panhandle especially in areas that are
more wind sheltered. Lows in the single digits below zero possible
Wednesday night in places, such as Gustavus and the Mendenhall
Valley.

.LONG TERM.../Thursday through Monday night/ Building upper ridge
over the Western US and Canada along with an increasingly negative
tilting trough over the Bering Sea and NE Pacific will bring
warmer and wetter weather to the panhandle through next weekend.
This overall pattern has not changed much compared to the guidance
from yesterday.

At the surface, forecast remains rather wet with warming
temperatures as overall south flow brings in a series of fronts.
There is a difference between ECMWF/Canadian and GFS/Nam on when
the precip will actually start late this week. ECMWF/Canadian
favor precip starting as early as Thu night for at least the
southern half while GFS/Nam hold off until Fri. Because of this
difference, chance pops remain in the forecast Thurs night into
Fri. First substantial front comes in Fri night into Sat with a
second front coming in Sat night. Temperatures initially appear
cold enough for snow for many areas Fri night but strong warm air
advection will warm quite a few areas up above freezing as early
as Sat afternoon facilitating a change over to rain. Haines and
Skagway will likely remain snow until possibly Sun afternoon if
they warm up that much at all. Precip may start to slacken off
toward late weekend and early next week as some guidance is
suggesting that the upper trough will tilt enough to pull most
systems farther west.

With the active forecast, winds will also be a factor. Outflow
winds in the inner channels will be shutting off, and then
switching to a southerly direction for all but Lynn Canal. Out in
the gulf, Friday and beyond will be mainly characterized by
nearly continuous 25 to 35 kt SE winds as one front after another
moves through. Wave heights will also be on the increase with 20
foot seas possible in the gulf by the weekend.

Few overall changes made compared to the previous forecast.
Temperatures for the weekend and beyond were raised a few degrees
and if guidance continues to show really strong warming may need
to be raised more in future forecasts. Otherwise, main changes
dealt with local effect in the mid range. Used mainly WPC for
updates.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through late tonight for AKZ025.
     Winter Weather Advisory until 11 PM AKST this evening for AKZ022-
     023.
     Strong Wind until midnight AKST tonight for AKZ018.
     Wind Chill Advisory until 9 AM AKST Thursday for AKZ018.
     Strong Wind until 6 PM AKST this evening for AKZ017.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Storm Warning for PKZ012.
     Gale Warning for PKZ011-013-022-031-032-034-043-051-053.
     Small Craft Advisory for PKZ021-033-035-041-042-052.

&&

DEL/EAL

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