Small Craft Advisory 16, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
257 PM AKST Fri Jan 5 2018

.SHORT TERM...According to current satellite imagery, the upper
level shortwave and its associated surface low located along the
western coast of Baranof Island has continued to lift across the
panhandle. The low center, now slightly less organized, can still
be seen cyclonically spinning just west of Sitka, but the feature
is continuing to weaken. Precipitation has transitioned to more
of a showery regime due to colder air wrapping into the low aloft,
which we can see from upper level potential temperature analysis.
On water vapor, the next front that will impact is currently
advancing across the gulf. This front is associated with a
shortwave embedded within a much larger trough positioned over the
Bering Sea. A moderately strong upper level jet streak is helping
to strengthen this shortwave, providing additional divergence
aloft, and providing additional moisture advection along the
front.

Winds, for the most part, will remain somewhat breezy through the
next few days, as once one front exits another will move in behind.
These frontal passages will cause brief bursts of wind along the
gulf marine waters and throughout the inner channels. Winds will
reach gale levels in some areas, especially along the eastern gulf
and through Clarence Strait, as our next front pushes through
early tomorrow morning. In addition, most of the central and
southern inner channel winds will reach Small Craft Advisory
levels and then rapidly diminish tomorrow afternoon as the front
exits the panhandle. Unfortunately, conditions should remain
fairly wet with this next front, and the challenge will be
determining what precipitation type will fall. Low level cold air
advection behind the weakening low will bring in sufficient cold
air at the surface to push things back below freezing, so precip
may start as snow and then transition to rain or start as a
rain/snow mix. But fear not! As the front leaves and our high
continues to build back in over Canada beginning Monday, we should
see a return to offshore flow. This means drier conditions and
cooler temperatures should be on the way for the early part of the
work week.

We did not make any significant or extensive changes in the
Saturday through Sunday timeframe. Most of our efforts were
concentrated on the Sunday into early Monday timeframe. There was
some model spread regarding a surface low that develops near
Haida Gwaii Sunday night, which added some uncertainty to the
forecast. Generally, we decided to use a NAM/GFS blend, with a
heavier emphasis on GFS, to add updates to the forecast.

.LONG TERM.../Sunday through Thursday night/ Overall upper level
pattern remains relatively the same as yesterday for early to mid
next week. Split flow pattern is dominate with a stationary ridge
over the Alaska mainland and an active south branch over the
gulf and NE Pacific with several short wave troughs moving east.
There is a general westward trend showing up with the position of
the upper ridge in recent model runs setting it up over the
central Alaska interior rather then right along the Alaska/Yukon
border like it was yesterday.

At the surface, the westward trend of the ridge is rather
significant for the panhandle as guidance is significantly colder
then what was depicted yesterday. The new scenario has a much
stronger cold air mass dropping into the southern Yukon early next
week bringing colder temperatures Tue and Wed. I began a drop in
temperatures at that time (around 3 to 5 degrees in some cases),
but I did not go as far down as models were suggesting to see if
future runs continue to support this new trend.

Otherwise, a generally drier forecast remains in place thanks to
the northerly winds still expected over much of the area at that
time and most storms directed to the south by the active southern
branch. Used more ECMWF with some Nam early on as the GFS was too
inconsistent with some features run to run. WPC used farther out.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 6 PM AKST this evening for AKZ027-028.
     Strong Wind from Saturday morning through Saturday afternoon for
     AKZ027.
     Strong Wind Saturday afternoon for AKZ028.
MARINE...Gale Warning for PKZ036-041>043-051-052.
     Small Craft Advisory for PKZ021-022-031-034-035.
     Small Craft Advisory due to Seas for PKZ053.

&&

Voveris/EAL

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