Small Craft Advisory 10, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
342 PM AKST Thu Jan 5 2017

.SHORT TERM...Weak low just off of Baranof Island this afternoon
continues to slide SE tonight spreading some showers (most of it
snow) across the southern panhandle. Visibilities have dropped to
1 mile at times in some of these showers with some low
accumulations observed. Behind the low, northerly outflow is
spreading across the northern panhandle. Winds are already blowing
gale force in Lynn Canal, 30 kt out of Taku Inlet, and satellite
scatterometer winds show 20 to 25 kt blowing out of the passes
east of Yakutat this afternoon.

For the next 24 hours, the main focus is the outflow winds. First
major push of cold air comes tonight as the surface high in Canada
builds into the 1040 mb range. Winds in Lynn Canal will increase
to storm force later tonight with gales for many other northern
inner channel and northern gulf areas. These winds will continue
into tomorrow and even strengthen a little into the afternoon
hours. As for land areas, the usual outflow areas will be howling.
Decided to issue a high wind warning for the Yakutat area, mainly
for the passes east of town. The high wind warning for Juneau
remains up for strong Taku wind gusts downtown. Cross barrier
flow is expected to increase to 60 to 80 kt by tomorrow afternoon
and there is a noticeable inversion above ridge top from all the
cold air flowing out of Canada. As for the critical level, there
is some directional shear around 600 mb for tonight but wind
directions switch to predominately NE across all levels by
tomorrow. So directional shear is not ideal but there is a level
of low wind speeds that persists around 600 mb through the period
that could easily act as our critical level instead. So the
likelihood of high wind gusts into fri remains high. Elsewhere,
strong wind headlines remain up for most of the northern inner
channels land areas tomorrow while the southern panhandle had
rather low winds.

Of somewhat less concern is the precip and clouds that will be
lingering over the southern panhandle. An upper level low that
will be lingering over the SE gulf by Friday will be the main
factor that causes that precip to linger. Most of the precip will
be due to bands of vorticity that will be rotating around the
upper low, but precip will be curtailed somewhat by the southern
extent of the outflow from farther north. Any precip is expected
to be light as a result and strong cold air advection into the
area will cause most of the precip to fall in the form of snow.
Any accumulations will be only a few inches at most across the
southern panhandle.

Most of the changes today were local effect edits for wind and
wave heights in the inner channels mostly using the Nam for
guidance.

.LONG TERM...Blocking system continuing to hold the active
weather pattern away from southeast Alaska. No significant weather
other than the wind related issues. The largest source of edits
for the mid to long range were in regards to temperatures.
Extended grids were nudged toward a Bias corrected MOS forecast.
For the Weekend lowered temperatures for the northern Third a few
degrees. A significant cold air pool sliding southeast past the
northern panhandle late Friday into Saturday. 925 MB temperatures of
-32C moved into the Chilkat valley and past White Pass, with upper
-20s flowing down Taku River Valley.

Winds across the northern panhandle had some minor adjusts up to
carry storm force to southern Lynn Canal into Friday night. The
Taku mountain wave looks to last a little longer than was
mentioned before so extended those as well and as result extended
warning for strong winds.

Raised seas for a fully developed status for the the Lynn Canal-
Chatham-Stephens-Frederick sound above standard procedure. Seas
of 12 to 15 for Southern Lynn Canal a possibility.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Warning from 3 AM Friday to 3 PM AKST Sunday for
     AKZ025.
     Strong Wind from 9 PM AKST this evening through Saturday
     afternoon for AKZ022.
     Strong Wind from 3 AM AKST Friday through Saturday afternoon for
     AKZ019-020.
     Winter Weather Advisory from 6 PM Friday to 3 PM AKST Sunday for
     AKZ018.
     Strong Wind until 6 PM AKST this evening for AKZ018.
     Strong Wind from 9 PM AKST this evening through Friday afternoon
     for AKZ018.
     High Wind Warning from 9 PM this evening to 3 PM AKST Sunday for
     AKZ017.
     Strong Wind until 9 PM AKST this evening for AKZ017.
MARINE...Heavy Freezing Spray Warning for PKZ022-035-043.
     Heavy Freezing Spray Warning for PKZ021.
     Heavy Freezing Spray Warning for PKZ053.
     Heavy Freezing Spray Warning for PKZ051.
     Heavy Freezing Spray Warning for PKZ011>013-031-034.
     Heavy Freezing Spray Warning for PKZ032.
     Storm Warning for PKZ012-013-022-043-051.
     Gale Warning for PKZ011-021-031-032-034-052-053.
     Small Craft Advisory for PKZ033-035-041-042.
&&

EAL/Bezenek

Visit us at http://www.weather.gov/Juneau