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586
FXAK67 PAJK 120131 CCA
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
255 PM AKST Tue Dec 11 2018

.SHORT TERM...Snow showers have returned to portions SE Alaska
this afternoon. Cold air advecting in from the west is helping to
produce both rain and snow showers. The convection becomes
enhanced due to the temperatures difference between the sea
surface and the cold air aloft, aka ocean effect. With broad W-SW
onshore flow, the showers have the best lift when they hit
mountain slopes facing that direction, ie. Juneau. Expecting some
accumulation out of these showers, 1-4 inches, amounts will be
highly variable since the showers will be scattered/intermittent
at times. Other locations will see rain showers become mixed with
snow through the evening as the CAA reaches them, even the
southern panhandle should have some flakes, but little to no
accumulation.

The convection is strong enough to produce some lightning as well.
Strikes have been detected west of Yakutat over Baranof Island,
and to a larger extent over the N. Pacific and Haida Gwaii. The
risk of thunderstorms remains through tonight, even over portions
of the inner channels. Ice pellets or graupel are typical with
showers like this, even if snow is not.

On Wednesday, a low will track ENE across the southern gulf. The
surface low looks to have more than one center and may rotate
about eachother in a Fujiwara effect. This tends to complicate
things as models struggle with which low to be most dominant, and
each usually picks a different one. We`ve stayed with the status
quo for the wind forecast overall. The GFS was a bit too strong
and the NAM was the slowest/furthest south. Still, models agree
that there will be a frontal band with high end gale force winds
over the gulf and into the ocean entrances. The band rotates
north, starting over the southern panhandle mid-morning and
spreading north to Juneau by evening. The position of the low puts
the northern half of the panhandle under some offshore flow,
resulting in lower POP. However, if the further northern model
tracks win out, then even Haines/Skagway will get into the action.
For now have left them at a chance as the low center shifts east
over the central panhandle on Thursday. After the low departs,
showers will linger on Thursday, but should be much fewer and far
between.

.LONG TERM.../Thursday through Monday/...Active weather pattern
continues through the weekend. A strong low will likely be in the
eastern Gulf to start Thursday. Models differ in how far north the
low will get as well as the timing and strength of the low to mid
level wave. Based on the low level wind fields and surface
gradients, looks like potentially another significant wind event
for parts of the southern Panhandle at least early Thursday. Over
the north, mid level deformation and a weak to northerly surface
gradient may allow for a period of snow to fall through Thursday
morning. Exactly where and how much snow may fall will also depend
greatly on the strength and track of the 850mb to 700mb
circulation.

There is good agreement towards the weekend of the continuation of
strong Pacific jet energy carving out another fairly deep
negatively tilted trough over the Gulf. With the propensity to
keep some sort of ridging over BC, this will likely lead to
another period of fairly wet and potentially windy weather,
especially for the south. While cold air does begin to deepen over
interior and western Alaska, there doesn`t seem to be much of a
mechanism to either get the cold air across the Gulf in a short
trajectory or to build substantial cold air in the Yukon. Thus, a
prolonged stretch of wintry weather does not look that likely at
least through the weekend with the exception of perhaps the far
northern Panhandle.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from Wednesday morning through Wednesday
afternoon      for AKZ027.
     Strong Wind Wednesday afternoon for AKZ022.
     Strong Wind from Wednesday morning through Wednesday afternoon
   for AKZ023.
MARINE...Gale Warning for PKZ022-035-036-041>043-051.      Small
Craft Advisory for PKZ012-013-021-031>034-052-053.

&&

$$

Ferrin/DEL

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