Small Craft Advisory 741, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
410 PM AKST Sat Nov 26 2016

.SHORT TERM...A front will be developing as it moves into the
region tonight from the west. Expect the southern panhandle to see
increasing clouds this evening and showers across the northern
panhandle to transition to more persistent stratiform
precipitation. Rain reaches the southern inner channels overnight
or early Sunday morning.

Rain/snow line was one of the more difficult forecasts today. The
Mendenhall Valley remains at 33F degrees this afternoon while
other places at the same latitude that have had wind shifts to the
SE, like Gustavus, shot up to the low 40s today. Warm southerly
winds have just increased through Lynn Canal as of 3pm, so expect
Haines/Skagway to see a mix of rain and snow at sea level.
However, inland/higher elevation locations will likely stay cold
enough to remain snow overnight. Have issued a Winter Weather
Advisory for those inland locations of the Haines/Skagway zones
through 9am Sunday for 3-7in of snow.

Over the outside waters, SE wind along the front will increase
30-40kt overnight. As the low tracks E-SE across the gulf, winds
will shift to the SW-W behind it and precip will transition back
to convective showers. Have continued with a slight chance of
thunderstorms in the forecast post front over the gulf.

Used mainly the NAM/GFS for updates to the forecast today with
some hi-res models and other adjustments for local effects.
Forecast confidence is average, but lower for temperatures and the
rain/snow line.

.LONG TERM...A triple point low will develop along the front noted
above near Cape Decision Sunday evening and move into the
Panhandle overnight. This will aid in drying the northern
Panhandle while keeping rain showers focused for the south. The
air mass temperature should not change significantly due to cloudy
skies to limit radiational cooling, so any snow that falls across
the north should be limited in amounts. What is left of the front
will spread scattered snow and rain showers over the north on
Monday. This has caused us to lighten winds across the north and
induce northerly winds across the Panhandle by late Sunday night.
Winds begin to transition to southerly/westerly on Monday as the
front moves into Canada.

Looking toward the south, a potentially storm force low will move
into the gulf out of the North Pacific on Tuesday. Today's guidance
has generally followed yesterday's track of the ECMWF carrying the
system toward Yakutat Bay. This is a trajectory that is very
efficient at pumping warm air into the Panhandle. In addition,
this system is loaded with subtropical moisture. NAEFS Mean
Integrated Water Vapor Transport suggests around 4 standard
deviations above normal for this, very wet, time of year.
Precipitation will begin in earnest around midnight Monday night
as snow across the inland central Panhandle. Juneau could
potentially see 2-4 inches on the front-side before a changeover
to rain Tuesday morning. We are still expecting 1 to 3 inches of
rainfall across the Panhandle with the rain/snow line surging
northward toward Haines/Skagway late Tuesday. For the Haines and
Klondike Highways, we are studying the possibility of a
significant overrunning event with the potential of well a foot of
snow plus from late Monday night into Tuesday evening. Confidence
is greatest for the highways and somewhat lower for the towns of
Haines and Skagway.

Winds speeds were increased across the Panhandle in accordance
with a low level jet anywhere between 40 and 75 kt Tuesday. Now we
have widespread gales for nearly all Inside Passages, and the
potential exists for damaging winds from the southern Inner
Channels, Prince of Wales Island, Baranof Island, Juneau, Skagway,
and Yakutat, although at this point, we should emphasize the
likelihood is small to moderate at this time...not in anyway
great. If confidence increases high wind watches may be issued in
the future.

Forecast has not changed post-Wednesday as focus remains on
Tuesday's major gulf storm.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 9 AM AKST Sunday for AKZ018-019.
MARINE...Gale Warning for PKZ036-043-051-052.
     Small Craft Advisory for PKZ012-013-021-022-031>035-041-042-053.
&&

Ferrin/JWA

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