Small Craft Advisory 666, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
250 PM AKST Thu Dec 28 2017

.SHORT TERM... The area of high pressure over the Yukon has set up
a strong gradient, such that it will be the perfect setup for
northerly outflow. Some of the northern inner channel waters will
see gale force winds. Skagway will see some of the highest wind
gusts across the panhandle tonight. The high weakens by Saturday
morning and shifts over central Canada. As this gradient weakens,
winds will decrease substantially early Friday, with the
exception of Skagway. The downtown Juneau and Douglas areas should
expect gusts up to 45 mph, but mountain wave guidance is
considered marginal with mediocre critical levels.

Minimal changes were made in pressure with any changes focused on
the tomorrow period. A blend of the GFS/EC/Canadian was used to
match WPC guidance, the GFS alone making the system too deep.
Changes within the wind grids were local edits on land. Winds were
increased for Day 3 along the outside waters, as a new low forms
near the Aleutian Islands late Saturday afternoon. As the pressure
gradient becomes more parallel into late Saturday, wind speeds
were decreased respectively over the inner channels.

Temperatures will remain quite chilly, with Friday night being one
of the coldest nights of the season. Most of the panhandle could
see single digits, and even negative temperatures in some areas.
As a result, maximum temperatures were actually lowered for
Saturday. POP's were edited using a NAM/GFS blend, which slowed
down Saturday's system somewhat and kept along with the dry
pattern. QPF models were keeping most of the precip offshore. Any
snowfall in the short- term period will be confined to the Yakutat
area, as a small front hovers over the area.

By Saturday morning, model differences provide little faith to a
solution.

.LONG TERM.../Saturday through Thursday as of 10 PM Wednesday/
Models maintain idea of blocky flow at high latitudes breaking
down by the end of the weekend. Pattern shifts to a broad upper
trof over the central PAC and ridging over the far E PAC and
western NOAM by early next week. Models hint at main longwave trof
and ridge positions will drift W some by the end of the week, but
differ on how far W the drift will occur. Overall, main
adjustment to the forecast was to slow the E progress of systems
into the area this weekend. This also slows down the moderation in
temps during the first few of days in long range.

With systems slowed moving E toward the area, have delayed the
precip threat some during the Sun-Mon period. Still a lot of
details to work out as well, such as whether any low pressure
waves form along the front as it moves into the area. Still a lot
of time to get this scenario worked out. Still going for warmer
temps moving in early next week with most places seeing above
freezing temps by Tue. This will change any precip over to rain or
a mix by then for much of the area. Toward the end of the week,
temps may cool some again due to potential W shift of longwave
features.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through late tonight for AKZ025.
     High Wind Warning until 9 PM AKST this evening for AKZ018.
     Wind Chill Advisory until 9 AM AKST Saturday for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Gale Warning for PKZ012-013.
     Small Craft Advisory for PKZ022-031-035-041.
     Small Craft Advisory due to Seas for PKZ032-042.

&&

SS/RWT

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