Gale Warning 235, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
256 PM AKST Mon Nov 27 2017

.SHORT TERM.../Monday night through Tuesday night/...Stratiform
precipitation turned convective very early in the day as evidenced
by satellite imagery, radar returns, and lightning detected in the
southern coastal marine zones. Snow showers resulted in very
erratic snow totals over the northern half of the panhandle with
only an inch or two in some locations to as much as 6 inches new
snow in Elfin Cove by 11 am and 7 inches at Bartlett cove as of
mid afternoon. Overnight snow showers produced 6 inches of snow
in Mud Bay as well. Meanwhile, in downtown Haines saw only 2.3
inches overnight. Afternoon satellite imagery is indicating that
shower activity is winding down. Next up is a low and associated front
advancing from the south that will clip the southern panhandle
with rain - snow for Hyder - before ejecting northeast into
British Columbia Tuesday afternoon. During this time there will
be a brief break in the action for the central and northern
panhandle, but by Tuesday evening, the next front will arrive.
This system will feature strong low level warm air advection that
will drive the snow level up such that only the Skagway will
remain in snow or a rain/snow mix. Snow is still possible late
Tuesday night from Icy Strait north with 2 to 4 inches of snow
currently in the forecast, but those places that do see
accumulations Tuesday night will then transition to rain. This
will make snow removal particularly difficult and potentially
impactful for road crews, homeowners, and airport managers.

Outflow winds have diminished considerably and only localized
small craft winds are expected over the inner channels through
Tuesday afternoon. Small craft advisories remain in place for the
coastal marine zones due to high sea states. The Wednesday front
will result in southeasterly gales for the coastal marine zones
by late Tuesday night...spreading inside with gales over Clarence
Strait and small craft winds elsewhere. As the snow turns to rain,
winds will diminish in the post frontal environment and a large
southwesterly fetch will set up over the gulf, driving the sea
state over the gulf to as high as 20 feet Wednesday night.

Little change to grids today as the focus was on shower activity
and accumulating snow. Most effort was spent on fine tuning
temperatures and snow level grids to account for sustained cold
temperatures in Haines today and in anticipation of the snow-to-
rain transition on Wednesday. Overall forecaster confidence is
average.

.LONG TERM.../ Wednesday to Monday/ Frontal band connected to the
large Bering Sea system moves across the gulf and into the
panhandle area Tuesday night and Wednesday. Still appears to be
period of warming of roughly 12 hours long ahead of the front,
that will be shifting the rain/snow line much closer to the Icy
Strait-Juneau line if not slightly north of there on Wednesday. A
secondary trough will lift northeast across the gulf late
Wednesday evening/night, and this should lead to another band of
organized showers spreading inland and this will also nudge the
warm sector of air southeast of the panhandle to the British
Columbia coast. Thus think the rain snow line will shift south to
be be between Icy Strait and Frederick Sound for the end of the
week and weekend.

Look for a band of Gale force winds with the front ranging from
35 to 40 kt for the outer waters, and trying to develop in
Clarence Strait as well.

General idea in the mid levels have a base agreement across the
ECMWF and GFS into next week, with differences not really big
until the Saturday-Sunday period. The upper level support of the
strong Bering system from Sunday will be moving Southeast from
the Bristol Bay to western gulf and then southeast as it opens to
a long wave trough headed towards the Oregon coast area by Friday
night. A ridge will build over the gulf behind the trough in
response to a large broad upper level low extending from the
western Bering west to Manchuria-Siberia region. Short waves in
the flow moving to the gulf for the weekend are being handled
slightly different and that may create forecast difference.

Overall few changes were needed to the forecast for Wednesday,
except warming temperatures to around 40 even into the far
northern channels to introduce rain into Haines and Skagway.
We added some local effects. Did also nudge temperatures down
Friday into Saturday as well across the panhandle. It looks as if
there is a small cooling trend of a couple degrees so started a
shift that direction then.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 3 PM AKST this afternoon for
     AKZ017.
MARINE...Small Craft Advisory for PKZ012-013-031-036-041-043-051-052.
     Small Craft Advisory due to Seas for PKZ022-042-053.

&&

Fritsch/Bezenek/EAL

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