Small Craft Advisory 766, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
351 PM AKST Mon Dec 5 2016

.SHORT TERM...Monday night through Tuesday night...

Coldest night of the season so far will occur tonight with clear
skies, diminishing winds and some snow cover promote optimal
radiational cooling conditions. Expect interior valleys of the
northern panhandle to plummet into the single digits by Tuesday
morning. Low temperatures across the central and southern
panhandle will fall into the teens and 20s.

The main focus over the next 36 hours will be a weak area of low
pressure moving into the central gulf. A weak shortwave associated
with this system will approach the area on Tuesday and into
Tuesday night. This will spread light snow across the northeast
gulf coast early Tuesday, spreading into the Elfin Cove area
around midday and eventually into the inner channels on Tuesday
afternoon. There remains subtle but important differences in
model guidance with the evolution of this system. Differences stem
from multiple factors, but most notably the strength of a northern
stream piece of energy. The 12z ECWMF is the weakest with this
feature which allows the system to take a farther northwest track
which would limit significant snowfall totals to the northeast
gulf coast. On the other hand the 12/18z NAM/GFS depict a stronger
northern stream which acts to suppress the system farther south
and east leading to more widespread snowfall across the northern
panhandle. Confidence in one scenario over the other remains low
so took a middle of the road approach. Highest confidence in
advisory level snowfall is over the northeast gulf coast and Elfin
Cove/Pelican areas so have issued a winter weather advisory for
those areas. Snowfall amounts taper off as you move inland. It
should be stressed this is a very low confidence forecast and any
shift in the track would result in changes to the snowfall
forecast. Later shifts will make necessary adjustments based on
latest satellite and model guidance. Stay tuned...

Winds will be on the diminishing trend through the period as the
pressure gradient weakens over the area. Expect the only winds high
enough for a small craft advisory by Tuesday afternoon to be in
Cross Sound.

Used the 12z NAMDNG/06z NMM for updates to the previous forecast.

.LONG TERM.../ Wednesday to Monday / The low in the northern gulf
will start weaken and pulling back westward mainly due to a short
wave diving southwards into the trough over the western Gulf of Alaska
and digging the trough southward. As the low shifts west, the
band of snow across the northern panhandle retreats west of Cape
Suckling by late Thursday. Cold high pressure continues to persist
over northwestern Canada for the foreseeable future.

The tighter pressure gradients should be reappearing across the
northern panhandle Thursday to Friday, as a surface low moves
onshore the the BC coast near Vancouver Island. This should
increase marine and outflow wind pattern back to gale force winds
again.

In the extended forecast the cold and dry pattern is expected to
persist in next week and the likelihood to locally windy in the
typical outflow areas. The mid to long range models are hinting
that some temperatures could rival the (this) Monday night lows.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory from noon Tuesday to 3 AM AKST Wednesday
     for AKZ022.
     Wind Chill Advisory until 9 AM AKST Tuesday for AKZ018.
     Winter Weather Advisory from 6 AM to 9 PM AKST Tuesday for
     AKZ017.
MARINE...Gale Warning for PKZ012.
     Small Craft Advisory for PKZ013-022-031-042-043-051-052.
     Small Craft Advisory due to Seas for PKZ041.
&&

TPS/Bezenek

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