Gale Warning 371, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
516 AM AKST Sat Dec 24 2016

.SHORT TERM...One more quiet short term forecast period before
things become active once again.

A weak ridge of high pressure over the eastern gulf extend north
and connects with a slightly stronger high pressure center over
the Yukon. The ridge over the gulf will shift east as the high
over the Yukon drops southeast into British Columbia through
Saturday night as a strong front moves east across the gulf. High
cloud cover from this front is climbing the west edge of the
surface ridge and has already arrived at the northeast gulf coast.
The 24 hour trend will be for increasing clouds from north to
south as the ridge shifts east and the front advances. In Yakutat,
flurries overnight changed to light snow by 3 am. Do not believe
this is associated with the front as of yet and have characterized
it as showers. Look for a transition to stratiform there later
today with 1 to 2 inches of snow falling between earl this morning
and early Christmas morning. As of now, am thinking that Yakutat
will be the only place to see any significant precipitation until
the beginning of the extended range forecast period.

A northerly/offshore pressure gradient remains over southeast
Alaska and the inner channels marine wind forecast reflects this,
but wind speeds are on the light side. Am starting out northern
Lynn Canal as a marginal small craft wind for this morning, but
that is it as far as advisories over the inner channels today. As
the front draws closer, look for a shift to the south. Small craft
southeasterlies will increase to gales over the coastal marine
zones. Residual offshore pressure gradient will act in conjunction
with the approaching front to produce small craft easterlies in
Cross sound tonight as well as southeasterlies in Frederick Sound
south of Cape Fanshaw. Finally, small craft southeasterlies will
develop in Clarence Strait late tonight. That will set the stage
for wind and snow late Christmas Day going into the early part of
next week.

No changes to pressure with minimal adjustment made to winds. PoP
from NamDNG5, NAM12, and SREF. QPF from NAM12 and NAMDNG5. Temps
adjusted per GFS MOS. Overall forecast confidence is average.

.LONG TERM...Several fronts and short waves will be moving
through the panhandle over the next week. However it is the storm
force front moving into the panhandle late Christmas Day that
garners the most attention.

The front will be bringing another round of winter weather with
precip expected to start out as snow for most areas of the
panhandle Christmas afternoon. How much snow certain areas will
get and when they will switch over to rain is the trickiest part
of the forecast as cold air depth (currently rather thin as there
is no deep strong cold air mass advecting in from Canada),
strength of the warm air advection and QPF are all factors. At the
moment, Hydaburg area will likely see the least snow with precip
quickly changing to rain in the strong warm air advection ahead of
the front. Klawock, Sitka, Ketchikan, and Annette are likely to
see a quick shot of 2 to 4 inches late Sunday afternoon before
temps warm up enough to switch to rain as well (Areas in northern
Clarance will likely see a little more snow before the snow
changes to rain). Areas farther north in the inner channels are
subject to the front gaining a slightly more east/west orientation
(increasing downsloping and slowing down the northward advance of
the rain/snow line) and the main upper level forcing aimed more at
the southern panhandle then the northern panhandle. Current
forecast has snow amounts of around 4 to 6 inches for areas from
Sumner Strait north to the Icy Strait area but if the upper level
dynamics track farther north (or south) snow amounts could end up
higher (lower) then currently forecast. Decided to not go for a
winter storm watch at this time as there are too many factors
present that could curtail higher snow amounts in the inner
channels.

In addition to the snow, Strong winds will be lashing the area.
Winds out in the gulf will be increasing to gale force Christmas
morning with storm force winds developing in the northern gulf by
Afternoon. For the panhandle winds will increase later in the day
with highest winds expected late Sunday afternoon into the
night. 850 mb jet streak winds only reach around 60 kt over the
area and the atmosphere will be rather stable so high wind gusts
are not expected but gust of 40 to 55 mph are likely across a
large portion of the panhandle Sunday afternoon into Sunday night.

Into next week west flow generally dominates with several
fronts/short waves moving through. None are as strong as the
Christmas Day front but they will still bring their own set of
rain or snow and some gusty winds. There are indications of
another possible dry period showing up for New Year's weekend as
a 500 mb ridge builds to our west but i will wait for model
scenarios to stabilize before completely committing to it.

&&

.AVIATION...Generally VMC conditions at the start of the day
south of Cape Fairweather with a few pockets of MVMC in areas of
low level convergence, such as vicinity Wrangell and Gustavus.
West of Cape Fairweather, MVMC due to CIGS and VSBY in snow
showers through the day today. Ceilings developing and then
lowering from north to south through the next 24 hours. No sig
turbulence of LLWS expected through the next 24 hours but that
will change by Sunday afternoon.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ043-051-052.
     Small Craft Advisory for PKZ012-022-034-036-041-042.
&&

Fritsch/EAL

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SPECIAL WEATHER STATEMENT
National Weather Service Juneau AK
310 PM AKST Sat Dec 24 2016

AKZ018>021-024>026-251500-
Taiya Inlet and Klondike Highway-Haines Borough and Lynn Canal-
Glacier Bay-Eastern Chichagof Island-
Eastern Baranof Island and Southern Admiralty Island-
Juneau Borough and Northern Admiralty Island-
Inner Channels from Kupreanof Island to Etolin Island-
Including the cities of...Skagway...Haines...Gustavus...Hoonah...
Angoon...Juneau...Petersburg...Wrangell...Kake
310 PM AKST Sat Dec 24 2016

...ACCUMULATING SNOW LIKELY CHRISTMAS DAY AND INTO MONDAY...

A strong weather front located over the west central Gulf of
Alaska as of Saturday afternoon will overrun a cold surface
airmass beginning Christmas Day to produce snow across most of
Southeast Alaska. Heaviest snowfall is expected between Sunday
afternoon and Monday morning with 24 hour totals ranging from 2
to 6 inches. Latest indications are snowfall amounts may be
slightly lower than previously forecasted over most of the central
and northern panhandle. The area expected to receive the most
snowfall is in Hyder where around a foot is possible as another
wave of low pressure crosses the southern panhandle on Monday. A
Winter Storm Watch has been issued as a result.