FXAK67 PAJK 172332
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
232 PM AKST Thu Jan 17 2019
.SHORT TERM.../Through Saturday/ Complex pattern aloft will make
for a tricky forecast, especially Fri night and Sat. Upper trof
will remain across NW Canada and E interior AK. Several shortwaves
will move N through SE AK and the eastern gulf during the period.
First main shortwave will move N into the southern area Fri, then
reach the N Fri night while weakening. Another shortwave will move
N into the southern area Sat. At the surface, high pressure will
remain over NW Canada, while a series of fronts move N into the
area. An occluded front will move N into the S area Fri, then
reach the N and weaken there Fri night. A low will move NNE to
the central BC coast Sat, with its associated occluded front
moving into the S Sat morning. Models have been struggling with
the second system, but seem to be honing in on the low track.
Main forecast issues will be how long any leftover fog will last,
how far N precip gets with the various systems, and winds. Areal
coverage of the fog has decreased quite a bit today with the
increased offshore flow drying things out. Still a little fog
around Yakutat, and some spotty fog over the more sheltered parts
of the inner channels. Offshore flow will continue to increase,
with drier air being advected in. Also, clouds will move in from
the S tonight, so expect much of the remaining fog to dissipate
or freeze out this evening. The place that might hang onto fog
longest is around Yakutat, as higher level clouds will stay S of
there for the most part, and outflow will take longer to become
As for precip potential, precip should move into the far S late
tonight or early Fri morning ahead of the first front. Models
suggest this front will remain strong enough for some of the
precip to reach the N by Fri evening, enhanced by a little
overrunning and deformation aloft. Could see a couple inches of
snow out of this front over the central area and parts of the N
Fri afternoon and night. The S may start as snow or a mix but
should become mainly rain by Fri afternoon as warmer air moves in.
Approach of second front and low will increase offshore flow over
the N, so the leftover frontal band there should dissipate early
Sat morning, and end any remaining snow associated with it. More
precip should reach the S Sat morning, with it being mainly rain.
Winds will be increasing some tonight as pressure gradient
increases between the NW Canada high and front approaching from
the S. Gales will continue in Lynn Canal, with SCA level winds
over much of the remaining northern inner channels. Keeping strong
winds going for Skagway through Fri as colder air will continue to
filter in. In the Juneau area, still some weak mtn wave activity
downtown, but this will likely diminish late tonight. Keeping
strong winds there through tonight. Offshore winds across the
central and S will increase some Sat as low and second front move
.LONG TERM.../Saturday night through Wednesday, as of 10 PM
Wednesday/ While the weekend continues to draw nearer, the
forecast continues to remain uncertain. Extreme shifts in
Saturday's low track continue with each new model guidance
provided. Synoptically, the period begins with 3 upper level low
pressure systems interacting with each other, the strongest of
which sits the border between northern Alaska and the northern
Yukon, and it will likely act to direct weather systems further
south from southeast Alaska's perspective. The other two upper
lows remain over the the northern Pacific. This leaves multiple
surface lows and fronts scattered over the southern gulf and
northern Pacific as well as a forecast situation.
Precipitation has trended further south. This drastically lowered
the snow amounts over the northern Panhandle as a whole.
Additionally with the more southern low track now favored in the
forecast gales are no longer expected over the Gulf.
Sunday the surface front driven by the more western upper low
over the northern Pacific looks to come ashore. Ultimately, wind
will not be very impactful Sunday; however, snow potential will
still exist briefly for the northern Panhandle before the warmup
likely begins. Monday through midweek, continues to look quite
wet and active; however, this will also mark a shift into a much
warmer weather pattern with highs pushing well above freezing by
the middle of the week for the vast majority of the Panhandle.
Forecast confidence is below average for the weekend and
adjustments are likely. Ensemble means and the NBM continue to act
as the primary guidance of the extended forecast. Fortunately,
next week shows much clearer signatures allowing for higher
confidence Monday into mid- week.
PUBLIC...Strong Wind through late tonight for AKZ025.
Strong Wind through Friday afternoon for AKZ018.
MARINE...Gale Warning for PKZ012-013.
Small Craft Advisory for PKZ021-022-031-032-036-041-042.
Small Craft Advisory due to Seas for PKZ043-051.
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