Heavy Snow in Alaska, January 9 to 10, 2020

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
309 PM AKST Thu Jan 9 2020

.SHORT TERM...Cold arctic high in place over Northwest Canada and
Alaskan interior. A moderate lower 980 mb surface low is moving
across the southern Gulf of Alaska. Warm frontal overrunning snow
event for the southern third. The main snow line looks to be just
south of the Frederick Sound. Southern Baranof Island should get
the good snow amounts while northern Baranof is expected to
lighter snowfall accumulations. Will be adding a Weather advisory
for the Hyder area for 8 to 10 inches of snow through Friday
night.

The tight pressure gradient along the coast mountains of the
northeast panhandle is resulting the in standard cold winter out
flow event. Max gales to storm force winds in the Lynn Canal
region, big seas and copious amounts of freezing spray out over
the northern inner channels. Very gusty winds near the interior
passes spreading the colder air into the panhandle.

The outflow event will persist longer than the snow event down
south, although the intensity may lift slightly with some of the
higher pressure in Canada re-organizing. Southern panhandle will
see improving conditions until they have dry weather by lat
Saturday.

.LONG TERM...The big weather stories of the extended range
forecast will be the arrival of particularly cold air to the area.
The upper level pattern starts out with notable ridge over the
Alaska mainland on January 12. This ridge will establish an omega
block which should help encourage outflow from the Yukon into the
panhandle. Guidance however remains in disagreement on just how
long this block will linger before getting pushed out. Operational
Canadian is rather progressive with it pushing out as early as
Monday. While the ECMWF, some ensemble means, opt for a slower
progression having some semblance of it sticking around in the
Yukon into early next week, with the GFS taking the middle ground
between the two.

This model uncertainty extends down to the surface with guidance
remaining in disagreement on just how much cold air will impact
the panhandle and how much of an effect gulf storms will have on
the area 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
strong northerlies of at least 35-40 knots 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
are currently progged to gradually decrease, dropping down to 25
to 30 knots in Lynn Canal and Taku inlet by Tuesday, but it's
possible that forecast values 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, while most areas are forecast to remain
dry through most of the forecast period, some precip could show
up, for the outer coast especially, if the actual outflow turns
out be weaker than currently progged, enabling precipitation from
offshore lows to actually make it to the coastline. Forecast
confidence at the moment is average.

&&

.AVIATION...IFR with ceilings and snow in the south. Wind shear
and turbulence near terrain with the strong winds.

&&

.MARINE...Gale to storm force winds in the northern inner
channels mainly Lynn Canal. Big seas and freezing spray into the
weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Warning from 6 PM this evening to 3 PM AKST Friday
     for AKZ023-026>028.
     High Wind Warning from 6 PM this evening to midnight AKST Friday
     night for AKZ025.
     Strong Wind until 6 PM AKST this evening for AKZ025.
     Winter Weather Advisory from 9 PM this evening to 9 PM AKST
     Friday for AKZ029.
     Strong Wind from 6 PM AKST this evening through late Friday
     night for AKZ019.
     Strong Wind through late Friday night for AKZ018.
     Wind Chill Advisory until 3 AM AKST Sunday for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ011-031.
     Heavy Freezing Spray Warning for PKZ013.
     Heavy Freezing Spray Warning for PKZ012.
     Storm Warning for PKZ012-013.
     Gale Warning for PKZ021-022-031>033-035-041>043-051.
     Small Craft Advisory for PKZ011-034-036-052-053.

&&

Bezenek/GFS

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