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FXAK67 PAJK 021734 CCA
AFDAJK

Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
834 AM AKST Fri Dec 2 2016

.SHORT TERM...Previous forecast with multiple weather warnings has
progressed largely as initially forecast. Changes made tonight
included adjusting the track of the storm force low as it comes
ashore and adjusting the timing of the winter storm warning for
the Klondike Highway.

Latest model guidance brings the weakening low ashore vicinity
Cape Spencer and then tracks it over Glacier Bay. By tonight, the
low will have crossed Lynn Canal and entered northwestern British
Columbia. Employed an ensemble approach to pressure grids and used
GFS as a foundation for winds over the gulf. Winds overnight as
of early this morning verifying well over the central and southern
panhandle, but are slow to increase over the northern inner
channels, to include Juneau. Maintained the high wind warning for
the downtown Juneau area for now, but will have to re-evaluate
this event by mid morning if things do not progress as expected.
Pre-frontal high winds verified in zones 27 and 28. Waiting now
for westerlies to pick up and hit the outer coast of Baranof
Island. Winds and wind gusts will diminish steadily through the
tonight period.

Low level warm air advection in advance of the low resulted in
temperatures remaining steady or rising overnight in several
central and northern locations. That will change late tonight as
colder air moves in first from the west and then from the north.
See the extended range discussion for additional details. With
warm low level air currently in place, snow is only an issue for
the highways. Opted to keep the Haines highway winter storm
warning unchanged and that is expected to expire by noon. Elected
to extend the warning for the Klondike highway through midnight
tonight since significant snowfall from the present weather system
is forecast to continue through the late evening. See the winter
storm warning product issued by this office for additional
details.

.LONG TERM...Long range period mainly deals with a switch to a
much colder pattern that sticks around through most of next week.
The cool down will be a one two punch affair. The first shot will
be incoming from the W and SW as the cold air wraps around a lee
side low in the northern gulf. Even though the air mass started
out in the arctic the warm gulf waters will have modified the air
mass by the time it gets here. However, 850 mb temps still drop to
-10 to -12 C by Sat night which will be plenty cold enough for
the remaining precip in the panhandle to change over to snow as
early as Sat afternoon. QPF values will be rather low so any
accumulations will only be around a few inches though some areas
could see some higher amounts due to convergence or convective
enhancement.

Cold shot number two shows up late Sunday coming directly from the
Yukon this time. This is the air mass that will cause temperatures
to plummet into the teens and 20s or lower early next week. The
results of this will be two fold. First, winds will change to the
north and rapidly increase in the usual outflow areas. Gales
expected for many of these areas. Freezing spray also expected
with the high winds and low air temperatures in the northern inner
channels. Second result will be the drying out of the panhandle as
the northerly winds push what precip is left southward. Main
forecast changes were in this time period as model trends had the
precip and accompanying weak low in the gulf slower to push out
then what was in there previously. Used mainly nam for guidance in
this period for details on the outflow winds and timing on when
the precip ends.

Extended forecast remains cold as the cold northerly winds
continue to feed cold air from the Yukon into the panhandle. There
are indications that it will not be dry though. Guidance is
suggesting that a gale force front may approach the panhandle mid
to late next week and with cold air still entrenched in the inner
channels it will likely be mostly snow that falls. Agreement on
the track of the main low is up in the air though as scenarios
range from a track into Haida Gwaii to it wandering around the
western gulf. About the only thing we can say with some certainty
is that there will be a storm somewhere in the gulf in the latter
half of next week.

&&

.AVIATION...MVMC conditions due to CIGS and VSBY prevail for the
upcoming 24 hours. Mod turbulence or worse extending well above
ridge tops with LLWS across the panhandle through tonight.
isolated thunderstorms possible on the inside but are most likely
along the central outer coast.

&&

.MARINE...A large portion of the gulf will see storm force winds
winds today with the largest swath out of the southwest in the
southern quadrant of the low. Southwesterly long period swell to
19 feet from Cape Ommaney to Cape Spencer, but biggest seas will
be south of Cape Edgecumbe and max out around 35 feet.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until noon AKST today for AKZ026-028.
     High Wind Warning until 9 AM AKST this morning for AKZ027.
     Strong Wind until noon AKST today for AKZ027.
     Strong Wind until 6 PM AKST this evening for AKZ021-022-024.
     High Wind Warning until noon AKST today for AKZ025.
     Strong Wind from noon today to 3 PM AKST this afternoon for
     AKZ025.
     High Wind Warning until 6 PM AKST this evening for AKZ023.
     Strong Wind from noon AKST today through this evening for AKZ023.
     Strong Wind through this evening for AKZ020.
     Winter Storm Warning until noon AKST today for AKZ019.
     Winter Storm Warning until midnight AKST tonight for AKZ018.
MARINE...Storm Warning for PKZ033-035-041>043.
     Gale Warning for PKZ012-013-021-022-031-032-034-036-051.
     Small Craft Advisory for PKZ011-052-053.
&&

$$

Fritsch/EAL

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