Winter Storm Warning 4, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
252 PM AKST Wed Jan 8 2020

.SHORT TERM...Cool to cold air in place over Southeast Alaska
will persist into the weekend. A very cold high sits over the
Alaskan interior and Northwest Canada. Tight pressure gradient
packing along the coast mountains so strong gusty outflow winds
are expected into the weekend. Looking to see storm force winds in
the Lynn Canal area. Also looking for the development of a Taku
Mountain wave wind event for the Downtown Juneau and Douglas areas
starting early Friday into the weekend. High Wind Watch issued
for the potential of 60+ mph gusts.

The cold temperatures and strong winds Skagway to White Pass are
causing cold wind chills to 30 to 40 below so and Winter Weather
advisory issued for that.

A weak trough this evening will spark some snow showers over the
southern portion of the panhandle with advisory level
accumulations, and again this is dependent on the showers moving
over the specific areas. Localized training of the showers could
result higher snow totals.

Another wave moving across the southern panhandle is expected to
spread snow back into the southern half of the panhandle. A winter
storm watch for snowfall has been posted for the overrunning
event of the warm moist air over the colder panhandle.

The northern panhandle should dry out and clear out for Thursday,
and could see some clouds move in on Friday. Forecast confidence
is slightly better than average to the weekend.

.LONG TERM...Extended range forecast is a little up in the air
as model disagreement starts to show up rather early in the
forecast. Upper level pattern starts out with notable ridge over
the Alaska mainland (possible omega block), but the disagreement
in guidance stems from how long this feature lingers before
getting pushed out. Operational Canadian is rather progressive
with it pushing it out as early as mon. While the ECMWF, some
ensemble means, and the WPC opt for a slower progression having
some semblance of it sticking around in the Yukon into early next
week.

This uncertainly extends down to the surface with different ideas
on how much cold air will assault the panhandle and how much
effect gulf storms will have on the area for next week. However,
the overall story still remains the same, it is just the details
that are in limbo. The general story is that cold outflow will
continue to rule the forecast for most areas of the panhandle for
the extended period. Expect northerlies of 25 kt or so around Lynn
Canal and Taku Inlet as well as other outflow areas and generally
dry conditions for most areas due to offshore flow. These winds
could go up or down as we get closer to the event depending on how
much cold air actually does make it to the area. Likewise, some
precip could show up, for the outer coast especially, if not as
much outflow appears. Forecast confidence at the moment is
marginal.

Given the notable disagreement between models tonight, any
changes were rather small or no changes were made at all. favored
the GFS and WPC guidance as they displayed a good middle ground
scenario.

&&

.AVIATION...Southern panhandle will see lower conditions due to
the snow tonight and clouds lowering to IFR or MVFR levels.
Northern panhandle's main issue will be turbulence near terrain,
and possibly low level wind shear if its near an interior passage
with outflow winds.

&&

.MARINE...Gale to Storm force winds in the next 24 to 48 hours
primarily due to outflow patterns. Bumped up the seas in Lynn
Canal and Chatham for enhanced fully developed or nearly so sea
states that will be above the standard wave forecasts for wind
spreads. Northern inner channels should also have light to heavy
freezing spray in the forecast as well.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Watch from Thursday evening through Friday morning
     for AKZ023-026>028.
     Winter Weather Advisory from 6 PM this evening to 6 AM AKST
     Thursday for AKZ027-028.
     High Wind Watch from late Thursday night through Saturday
     evening for AKZ025.
     Strong Wind from late tonight through Thursday afternoon for
     AKZ025.
     Strong Wind through Thursday afternoon for AKZ018.
     Wind Chill Advisory from midnight tonight to 3 AM AKST Sunday
     for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Heavy Freezing Spray Warning for PKZ013.
     Gale Warning for PKZ012-013-022.
     Small Craft Advisory for PKZ021-031-032-041>043-051>053.

&&

Bezenek/EAL

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