Winter Storm in Alaska, December 10 to 11, 2017

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
307 PM AKST Sun Dec 10 2017

.SHORT TERM...Strong storm force low in the gulf and a sweeping
frontal system are bringing strong winds for the outer coastal
zones south of Dry Bay this evening, then heavy rain developing
overnight...except heavy snow for White Pass. A succession of
shortwaves will pass over the panhandle Monday.

Winter Storm Warning will begin at 6 pm this evening with total of
12 to 16 inches expected overnight and Monday morning. The main
idea here is for temperatures to remain cold enough for snow at
White Pass with warmer temperatures moving in by afternoon. Snow
amounts should reach around 1 to 1 1/2 feet, then quickly shrink
with the wet heavy snow and possible rain during Monday afternoon.

Models are in good agreement and differences in model runs was
minor. Used GFS/NAM to nudge winds down mainly in the gulf
starting Monday night through Tuesday, minor local changes in the
early periods. NAMnest and SREF was the favored models for
POP/QPF.

Confidence remain good for the incoming system with slightly less
confidence to exact snow levels and snow amounts.

.LONG TERM /Tuesday through Saturday/...As of 10pm
Saturday...Active weather pattern continues through the extended
forecast. Multiple lows/fronts will track across the gulf south to
north through mid week. Timing of breaks between weather systems
is difficult to pin-point as models have differed from run to run.
That is to say, majority of the week will be wet. The warm
temperatures continue through mid week with rain being the
predominant p-type (exception being White Pass) then things start
to cool each day through the end of the week. This is due to a
shift in the jet stream from S-N and pointed at the panhandle with
a direct stream of moisture from the tropics to a more zonal W-E
jet and shifted south. As a result, weather systems will be moving
across the gulf from the west and the end of the week has some
snow mixed into the forecast across the northern half of the
panhandle.

Majority of the week will see southerly winds across the marine
waters. Expect 25-35kt winds with each frontal band. Seas will also
remain rough or very rough, with the outside waters staying above
10ft, as there will not be a long enough break for things to lay
down.

Most adjustments to wind were minor since new model pressure fields
were not significantly different than the previous forecast.
Where models were in agreement on fronts, POP was adjusted up, and
vice versa where models differed POP was lowered to chance.

&&

.AVIATION...Periods of wind shear, increasing winds and
deteriorating conditions will be part of the forecast as the next
frontal system passes through tonight into Monday. Improving
conditions through the day Monday.

&&

.MARINE... Storm force winds will be present in the Gulf and
portions of coastal water zones, coinciding with the timing of
the deepening low. Much of the inner channels and Yakutat Bay will
be under a small craft advisory through Monday. This threat will
diminish into Monday morning as the frontal system passes.

&&

.HYDROLOGY...Most small streams and rivers will experienced a
small increase due to heavier precipitation, but none are
expected to reach bankfull stage.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until midnight AKST tonight for AKZ027.
     Strong Wind from 6 PM to 9 PM AKST this evening for AKZ022-023.
     Winter Storm Warning from 6 PM this evening to noon AKST Monday
     for AKZ018.
MARINE...Storm Warning for PKZ043-051-052.
     Gale Warning for PKZ022-041-042.
     Small Craft Advisory for PKZ012-013-021-031>036-053.

&&

KV/Ferrin

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