Small Craft Advisory 39, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
259 PM AKST Fri Jan 18 2019

.SHORT TERM.../Through Sunday/ Upper trof will remain across
interior AK and the Yukon through Sun. A series of shortwave trofs
will move into the area through Sun. First shortwave will move N
across the central area tonight before dissipating by early Sat
morning. A stronger shortwave will move N into the southern
panhandle Sat, then weaken as it moves NE of the southern area Sat
night. A third shortwave trof will move into the northern gulf Sat
night, then move toward the northern panhandle Sun. At the
surface, a trof over the southern panhandle will drift N and
dissipate over the N-central area tonight. A low will move N to
the far southern panhandle by Sat evening, then weaken to a trof
as it continues N into the central panhandle Sat night. this trof
will merge with another trof moving NE across the gulf, and reach
the northern panhandle by Sun evening. 12z GFS was main model of
choice, but most others were very close (except the 12z NAM).

Main forecast concerns will be precip potential/ptype/snow amounts,
and winds. Some light snow is falling over much of the central
panhandle late this afternoon as some weak overrunning enhanced by
mid-level deformation was occurring. This will continue through
the evening hours, then diminish rapidly overnight tonight as
offshore flow increases ahead of the low moving N toward the
southern area. Could see an inch or 2 of snow across the central
area tonight. Precip should be rain across the S tonight,
although there may be a break in the precip during the late
evening. After another break for much of Sat, more rain should
push in late in the day and continue Sat night across the S with
low moving in. Eventually, by Sun afternoon, the combined trof
that forms will spread some precip back across the central and N
areas. Think most of the precip should remain snow from Juneau
northward, while areas to the S will be rain or a mix. Could see a
couple inches of snow sun afternoon over the N-central area.

Strongest winds will remain in Lynn Canal through Sat evening.
Gales should continue there during that time, then lower to SCA
levels Sat night. The central inner channels will see SCA level N
winds diminish by Sat evening. Could see SCA level winds across
the SE gulf tonight as well. Some of the outflow into the NE gulf
could also reach SCA levels through Sat.

Otherwise, lowered temps some across the N through the period, as
colder airmass will take longer to erode away.

.LONG TERM.../Sunday night through Thursday, as of 10 pm
Thursday/ Overall pattern for the long range looking rather warm
and wet for the most part. A ridge over the Pacific NW with a
trough over the Bering Sea keeps SW flow over the gulf and
panhandle for the entire period. Funneling warmer marine air and
wetter conditions into the panhandle. Several short waves are
embedded in the flow but the timing of these short waves remains
rather uncertain at this time.

At the surface, the uncertainty in the upper level short waves
translates into the surface features as well. The first of these
approaches the panhandle from the SW Mon night. Whether this
feature will be in the form of a low or an open trough is
debatable. As is where it will actually track if it is a low
(with suggestions ranging from the central gulf to the Dixon
Entrance area). Decided to leave the depiction of it as a trough
but increase winds in the eastern gulf to 25 kt and have pops
remain at categorical to get a little more of an indication that
something is moving through at that time.

Second feature appears to be actually two fronts that will mainly
focus on the northern gulf coast Wed into Thu. Noticeable
differences on timing and how far east various models tend to take
the precipitation, but general trends favor a wet mid week period
especially for the northern gulf coast and northern panhandle.
There are some indications that this may turn into an atmospheric
river event for the northern gulf coast into Thu, but where
exactly this will set up is not clear. Forecast confidence as a
result is rather poor for mid next week.

Throughout all of the long range the main message remains that the
forecast will be wet and rather warm with most areas likely
melting at least part of their present snow pack. Forecast updates
used mainly the WPC data.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ012-013-021-022.
     Small Craft Advisory for PKZ031>033-036-041>043.
     Small Craft Advisory due to Seas for PKZ051-052.

&&

RWT/EAL

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