Gale Warning 70, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
335 PM AKST Thu Feb 15 2018

.SHORT TERM...Mid/upper trough currently over the northern
Panhandle this afternoon will continue to track SE over night as
ridging reasserts itself over the eastern Gulf. Next significant
upper trough over the Bering Sea will split as it encounters the
eastern Gulf ridge with the most significant piece of energy
slide SE towards Haida Gwaii by late Friday night. Associated
stronger surface low will move eastward across the southern Gulf
on Friday night and pass south of Dixon Entrance early Saturday. A
strong northern stream shortwave will then dive south from NW
Canada through the Panhandle by Saturday afternoon.

Currently, main axis of precipitation is along the coast mountains
from Juneau southward to the Ketchikan area with shower activity
to the west. As colder air aloft moves eastward under the upper
trough, will likely see lapse rates steepen late this afternoon
and early this evening, which combined with favorable orographics
in the low levels, could enhance the snowfall from Juneau into the
Petersburg/Wrangell areas. Kept current winter headlines as is but
bumped up amounts into the 4 to 6 inch range. Could see a few
isolated higher amounts but think the increasingly showery nature
of the snowfall and the relatively quick moving upper trough will
limit widespread warning amounts. Surface temperatures are
marginal over the southern Panhandle from Klawock to Ketchikan so
although it is snowing there, warm boundary layer will limit
accumulations. A quick couple of inches in the heavier rates is
not out of the question though.

Main concern after tonight as increasing outflow winds as the low
slides south of Dixon Entrance Friday night and Saturday.
Increasing cold advection in the low levels and deep layer
northerly flow aloft will drive storm force winds down Lynn Canal
by early Saturday. Position of the surface high to the NW of the
Panhandle initially will favor outflow in the N/S channels with
strong northerly winds likely extending down Chatham Strait. Mountain
wave guidance is indicating a period of favorable conditions
Friday night as deep outflow commences over Salisbury Ridge. Lack
of a true weakness in the flow aloft near 500 mb may be the
limiting factor on sustained high winds but gusts between 50 and
55 mph will likely occur by late Friday night near downtown
Juneau/Douglas.

Models are overall in good agreement through Saturday which lends
to a higher confidence forecast.

.LONG TERM.../Saturday through Wednesday night/...Active upper
level pattern for the up coming week, but little action at the
surface apart from some windy conditions on Saturday.

Extended range forecast begins with a slightly negatively tilted
upper ridge situated over the western gulf and Alaska Peninsula.
An upper short wave will be dropping south over the panhandle and
then dig an upper trough Saturday night over Vancouver Island.
The upper ridge will shift east as a strong upper trough shoves in
from the west on Sunday. The trough will eventually flatten the
ridge and ride over the top, then spin up a small upper low over
the southern gulf on Monday morning. Another larger upper ridge
will build in behind the upper trough and dominate the gulf, the
interior through Wednesday. Another strong upper trough will sweep
east across the gulf on Thursday and the dive southeast Thursday
night.

At the surface, a gale force low will be cutting under the
Panhandle on Saturday. Interaction between this low and building
high pressure over the Yukon will increase the northerly gradient
and Saturday looks like it will be quite a windy day over the
northern and central inner channels. As the low continues to move
off to the southeast, high pressure over the Yukon will weaken as
well. The northerly pressure gradient will weaken on Sunday and
remain weak for much of the next week. Long range models are
indicating the possibility of a low tracking across the northeast
gulf late next week.

Southern Prince of Wales Island may see some precipitation
Saturday morning. Apart from that, Southeast Alaska will remain
cold and dry until at least mid week next week...if not longer.

Winds for Saturday and Saturday night were diminished slightly
over the southeastern gulf and to even a lesser degree over the
northern inner channels. Even so, am expecting gales over Lynn
Canal and Stephens passage. Also think strong
northerly/northeasterly winds for Haines, Skagway and Juneau are
probable. Overnight lows mostly unchanged, but daytime highs were
reduced slightly. Overall forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 9 PM AKST this evening for AKZ026.
     Winter Weather Advisory until 6 PM AKST this evening for AKZ025.
MARINE...Small Craft Advisory for PKZ012-013-022.
     Small Craft Advisory due to Seas for PKZ041>043.

&&

DEL/Fritsch

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