Small Craft Advisory 4, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
648 AM AKST Wed Jan 4 2017

.SHORT TERM...The inversion we have experienced over the last
several days has weakened, yet it still exists. Areas of dense fog
therefore continue to plague the central Inner Channels. A dense
fog advisory remains until noon today for 20, 21, 25 and 26.
Light winds will continue through tonight as the bulk of the
Panhandle remains under a zone a weaker low pressure situated
between high pressure centered over the western gulf and cold high
pressure over northwest Canada. However, winds will increase
through the far northern Panhandle and Lynn Canal tonight as a
short-wave induces lower pressure as it drops east southeast from
Mainland Alaska across the Wrangell St. Elias Range. Cold air
advection will begin through the Chilkat Valley and down the
Klondike Highway and help sustain increases in both Haines and
Skagway especially late tonight.

Fog will likely re-form tonight across the central and southern
Panhandle as models are indicating the inversion persists, but
continues to weaken. However the short-wave mentioned above
may assist with mixing out the lower boundary layer late tonight
from north to south. Therefore we trended downward both fog
severity and expanse through Thursday morning from north to south.
So confidence in fog expanse after midnight is less than for the
evening hours.

Few changes were made. The majority of time was spent on fog
progression.

.LONG TERM...Little change to synoptic reasoning for extended
forecast as models continue to indicate a vigorous shortwave
dampening the ridge as it dives SE across the panhandle Thu with
a cold air mass advecting into the region in its wake. Models
continue to indicate potential for precip, but, given the dry
airmass currently in place, believe models too aggressive
developing precip over the northern panhandle Thu with better
precip chances further S.

Pressure gradient will tighten quickly as CAA develops in the
wake of the shortwave. Pattern still favors strong outflow
developing Fri and persisting through the weekend. NAEFS standard
anomalies show 1000mb and 850mb temps 1-2 standard deviations
below normal Thu through the weekend and continue around 1
standard dev below through the extended. NAEFS anomalies also
enhance confidence in strong winds with 850mb winds 3-5 standard
deviations above normal over the northern panhandle this weekend.
GEFS RMOP also lends towards above average confidence in the
overall pattern.

Gale to storm force winds will develop over the inner channels
and favored outflow areas Fri-Sun and freezing spray is expected
over much of the inner channels. Ingredients for a strong Taku
wind event are also in place with very strong cross barrier flow,
cold air, and a good critical level. So high wind gusts are
expected for downtown Juneau and Douglas late this week and
weekend before winds gradually diminish into early next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Dense Fog Advisory until noon AKST today for AKZ020-021-025-026.
MARINE...Small Craft Advisory for PKZ012-013.
&&

JWA/BC

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