Small Craft Advisory 30, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
629 AM AKST Wed Jan 10 2018

.SHORT TERM...The northerly outflow regime will begin to
transition to wetter warmer pattern by the weekend. The cold upper
level trough over the central Panhandle continues to propagate
southward this morning. At the same time a short wave trough
pushes northeast across the gulf and Panhandle. With scattered
snow shower activity still ongoing over the central Panhandle,
this short wave could act to enhance the showers and begin to lift
them northward late this morning.

Northerly outflow remains ongoing this morning; however, the
strongest winds have passed and winds will decrease through the
day. Windiest areas remain Lynn Canal, Downtown Juneau, Douglas
Island, and Cross Sound.

A weak weather front will begin to move into the eastern gulf late
tonight; however, precipitation associated with it will remain
offshore. A stronger front will move northeast into the gulf by
Thursday night. This front will produce a widespread precipitation
event over the Panhandle on Friday. Coupled with the cool
temperatures from the ongoing outflow event, precipitation
associated with this front will begin as snow before transitioning
to rain.

Primary changes to the short term forecast involved increasing
shower activity this morning as well as adding isolated showers to
the northern Panhandle tonight as the shortwave passes over. Winds
were increased over the gulf along the approaching fronts; they are
currently capped at 40 kts. Primary guidance was a blend of the
06Z NAM and NAMnest with some input from 00Z GFS.

.LONG TERM.../Friday through Tuesday/ There will be several
transitions over the long-term period starting off with cold and
wet, then warm and wet, and finally warm and dry heading into
Tuesday. The pattern sets up with a ridge axis to the east of the
panhandle and a low tracking northeastward through the Gulf by
Friday. However, some uncertainty is brought into the mix between
individual model runs due to several wave features that will
propagate in between this synoptic scale pattern.

Minimal changes were made to the pressure field and edits to wind focused
mainly in Gulf and local edits due to wind shifts. Again, GFS was
the outlier in wanting to push these next frontal systems farther
north of other solutions.

There will be a large band of WAA late Thursday into early Friday
that will extend from the Aleutian Islands through the southern
panhandle. As a result, weekend temperatures will be quite warm,
or at least warmer than they have been. With the warming trend,
temperatures will peak on Sunday, before dropping down steadily
again. Maximum temperatures were nudged slightly using an EC
bias-corrected blend. Minimum temperatures were kept warmer based
on cloud cover and current WPC guidance. Even 500 mb temperatures
are showing ranges in the negative teens, which is anomalously
warm for this time of year.

As far as precipitation, there will be several changeovers from
rain to snow and back to rain during the Saturday timeframe. The
timing of this remains uncertain. Most models were wanting to go
categorical, but we kept POPs at likely at most for Day 5 onward
using a NBM/WPC blend and SREF early on. We are starting to see
increases in QPF amounts, especially during the late Saturday
timeframe.

Overall, there is not much confidence in model agreement. While
the large-scale pattern seems reasonable, confidence is lower for
individual waves in specific timing and tracking.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until noon AKST today for AKZ025.
     Strong Wind until 6 AM AKST early this morning for AKZ018.
     Wind Chill Advisory until 9 AM AKST Thursday for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Heavy Freezing Spray Warning for PKZ012.
     Gale Warning for PKZ012-013-022-031-032.
     Small Craft Advisory for PKZ011-021-033>035-041>043-051>053.

&&

JB/SS

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