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FXAK67 PAJK 162341

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
241 PM AKST Sat Dec 16 2017

.SHORT TERM.../Saturday through Monday as of 1 PM Saturday/

The weather front affecting the Panhandle has pushed through the
northern Panhandle and has almost made its way through the
southern Panhandle. Behind the front widespread shower activity
is expected through the evening. An area of interest is the far
northern gulf and the eastern gulf over the next 24 hours where
steeper lapse rates (faster cooling with height) will create a
more unstable atmosphere and allow for a chance of thunderstorms
in those areas. Sunday night through Monday a surface low will
track southeast through the gulf acting to keep the Panhandle wet.
Shower activity will diminish Monday from north to south as the
low tracks southeast. Surface high pressure builds over the gulf
and Panhandle behind this system which will act to dry southeast
Alaska out as Monday progresses.

Winds are primarily a concern this evening as mainly over the
northern Panhandle and with tip jets near Cross sound and Cape
Decision. Strongest winds will be near Skagway and gales will be
present in northern Lynn canal and near Cross Sound.

The seasonably warm above freezing temperatures decrease through
the short term. However, with the coolest temperatures being
Monday not much snow is expected across Southeast Alaska since
this will be the drying day for the Panhandle.

Not many significant changes were made in the short term. Primary
guidance was a blend of the GFS and ECMWF with some input from the
NAMNest and ARW to handle the shower activity behind the front.
POP was increased to allow for more widespread shower activity
this evening. Confidence is above average in the short term.

.LONG TERM.../Monday through Friday/ As of 10pm Friday

Yet another anomalously strong upper ridge continues to be
advertised by both operational models and their ensembles to
rapidly build over the Gulf of Alaska next week. Cool upper trough
over the northern Gulf early on Monday will quickly be shunted off
to the southeast ahead of this building ridge. Lingering shower
activity on Monday will likely be in the form of snow even to sea
level for the northern and interior inner channels from Haines
and Juneau as far south as Petersburg. Only light precip amounts
are expected and this will primarily be a case of the cold air
chasing the moisture so any snow accumulations would be minor.

Still looks like a very brief offshore flow even late monday into
Tuesday. Northerly winds will develop over the northern inner
channels on monday as the weak low offshore slides to the south.
Light northerly flow through the low levels will promote at least
some clearing by Monday night and Tuesday although will need to
watch for fog in places that are sheltered from the wind as the
ground will be saturated.

Low level flow becomes more NW`ly on Tuesday night into Wednesday
which is not necessarily a clear sky direction at times. Could see
some low level moisture and stratocumulus try to make a return
along the outer coast, however Wednesday should be another dry

Upper ridge begins to shift east by late week with a series of
storm systems and their associated deep plumes of moisture riding
up the west side. At this time it appears the ridge will hold
strong enough to keep the deep fetch of moisture mainly to our
west, with only weakening fronts approaching from the west by
Thursday/Friday. Unfortunately for snow lovers, we are hard
pressed to find any significant hope for snow in the future as
freezing levels rise to around 5 kft by late week under the strong
ridging aloft.


.AVIATION.../As of 130 pm Saturday/ Most of the Panhandle is
behind the front besides the far southeast Panhandle. Shower
activity will be widespread behind this system through tonight.
This will keep conditions primarily MVFR; however, as stronger
showers pass through expect short periods of IFR conditions. In
addition to the lower ceilings and visibilities associated with
showers, westerly low level windshear will exists over much of the
panhandle through tomorrow morning. Shower activity will begin to
diminish late tomorrow.


.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Warning until 3 PM AKST this afternoon for AKZ018.
     Strong Wind from 6 PM AKST this evening through late tonight for
MARINE...Gale Warning for PKZ012-022.
     Small Craft Advisory for PKZ013-021-031-032-034-036-041>043-051-
     Small Craft Advisory due to Seas for PKZ053.




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