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983
FXAK67 PAJK 211440
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
540 AM AKST Sat Jan 21 2017

.SHORT TERM...High pressure will remain over the Yukon through
tonight. A weak trof will develop N into the eastern gulf tonight.
Weakening shortwave trof will move NW into the SE gulf late
tonight.

Main forecast concerns will be winds, cloud cover, and potential
for precip. Right now, strongest winds are over the N inner
channels with 35-50 KT N winds over most of that area. Models
suggest the pressure gradient will weaken slowly this afternoon
and tonight, which should allow winds to decrease in that area.
In the Juneau area, a Taku wind is occurring downtown and near
Douglas with gusts to 70 mph. These winds should weaken late this
morning and afternoon as cross barrier flow weakens some. Keeping
the HWW going until 18z for the Taku winds. Other areas will
generally have SCA level winds on the inner channels...and 20-25
KT over the outer waters. Will maintain wind chill advisory for
White Pass for this morning as well.

Clouds right now are mostly high and thin. As warm advection
develops in upper levels this afternoon and tonight, thicker high
clouds and some mid-level clouds will move in. As shortwave trof
and weak sfc trof develop tonight, clouds will thicken and lower
over the gulf and far southern area.

Precip potential will be mainly with the weak trof over the gulf
and shortwave trof moving into the SE gulf. Think most of the
precip that develops initially will remain over the gulf, but some
may clip the far S area late tonight as precip begins to expand in
areal coverage.

.LONG TERM...Period begins with an upper trough digging into the
gulf from S central AK. Models in fairly good agreement this
perturbation will move across SE AK into Mon as a surface wave
develops over the gulf. Precip will gradually move into the outer
coast Sun and expand Nwd into the N central gulf by Sun
afternoon/evening, then push E across the panhandle Mon. Enough
cold air will remain over the region for an precip to begin as
snow before warm air advection takes over and changes precip to
rain. Light accumulations expected across most of the area Mon before
N winds diminish and shift to Sly. As this initial WAA works N,
hi-res guidance suggest the potential for some patchy freezing
precip possible, however, areas coverage remains very spotty and
shifts significantly from run to run. The real warming takes hold
Tue as a deep upper low moves to 55N/165W. This will result in
deep SW flow developing across the panhandle with a series of minor
perturbations ejecting across the region. GEFS progs low level
temps warming to about 1-1.5 standard deviations above normal, so
precip type at sea level will be all liquid except for the far N
panhandle. These quick moving systems will have limited moisture
so do not anticipate more than an couple of inches of snow. This
pattern will persist through mid week before models prog a strong
ridge to build over BC and shift W. This ridge is supported well
by ensembles and GEFS shows pretty good predictability so expect
drier weather heading into the weekend. Minor changes to inherited
forecast mainly for adding temporal resolution.

Biggest challenge remains ptype/potential snow amounts with first
wave Mon-Tue. Latest guidance progs the low remaining further
offshore, so colder air may persist longer, but precip amounts
would be be limited.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Warning until 9 AM AKST this morning for AKZ025.
     Strong Wind from 9 AM AKST this morning through this afternoon
     for AKZ025.
     Wind Chill Advisory until 9 AM AKST this morning for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ031.
     Heavy Freezing Spray Warning for PKZ011-012.
     Heavy Freezing Spray Warning for PKZ013.
     Storm Warning for PKZ012.
     Gale Warning for PKZ013-031.
     Small Craft Advisory for PKZ011-021-022-032>036-041>043.
     Small Craft Advisory due to Seas for PKZ051.
&&

$$

BC/RWT

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