Area Forecast Discussion
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FXAK67 PAJK 272226
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
226 PM AKDT Thu Apr 27 2017
.SHORT TERM.../Tonight through Saturday/ 1002 mb low spinning 60
miles WNW of Sitka is currently bringing wet and breezy conditions
to many areas of the central panhandle as the second wrap of the
associated front moves inland. Gusts around 25 to 30 mph have
been recorded at Sitka, Angoon, and Juneau so far this afternoon.
This low will gradually move inland S of Cross Sound this evening
and is expected to weaken over the northern panhandle tonight. W
winds of around 15 to 25 kt are present on the S side of the
system and will be hitting the central outer coast for much of the
night. Some of this will bleed over into the northern inner
channels as well. Ended up raising winds for tonight`s forecast over
what was previously there using hires nam with some inner channel
areas seeing up to 25 kt out of the south at times tonight. Winds
are expected to diminish as the system rapidly weakens late
Showers continue through Fri night, particularly over the northern
panhandle, as onshore flow in the wake of the low persists. A
building ridge will gradually shut those showers off, but it will
only be when offshore flow develops ahead of the next low on Sat
that the showers shut off completely. The weekend is looking
rather dry for the north with persistent offshore flow. Meanwhile
the southern panhandle will be dealing with increasing clouds,
wind, and precip as a 996 mb low moves NE toward Haida Gwaii.
.LONG TERM.../Saturday to Thursday/ Ridging over the eastern gulf
and panhandle expected to shift into British Columbia as an upper
level trough/closed low moves into the southeastern gulf. 500 mb
vort max band associated with this trough may lift northward late
Saturday as ridging builds again over the central gulf and then
into the eastern gulf through Sunday. Upstream a large deep upper
low moves over the Aleutians and remains quasi stationary through
mid week with the ridge remaining over the eastern gulf and
panhandle. By the end of the week this broad upper low will
likely shift east but uncertain on the exact track.
At the surface on Saturday there is be a weak low in the northwest
gulf with a developing low tracking south of the eastern gulf.
Lots of model spread on the track of this system, and with the
position of this low track differences will result in large
forecast variation. Best estimate is the low will move near Haida
Gwaii through Saturday and likely dissipate by early Sunday
morning. Seems to be a trend of models moving the low center
further south which will have more offshore flow for the northern
regions, thus drier weather, compared to the south which will
have greater chance for rain. Nudged winds from this system
toward small craft levels in the southeast gulf. GFS/Canadian have
trended further north with stronger winds than the ECMWF/NAM
which also dissipate the low sooner. Decided best option was a
compromise blend until we get better model resolution. Beyond the
weekend models fell more in line with the next surface low near
the Aleutians the the associated occluded front moving into the
gulf Monday into Tuesday. Later in the week a much stronger low
appears to track up from the southwest and will have more impact
with respect to winds/pop/qpf.
Once again the word of the long range is uncertainty, especially
for the weekend. RMOP values below 30% with the weekend low.
Values improve later in the week as the next systems move in and
model align. Used a blend of GFS/ECMWF for Saturday even though
they were not in great agreement. Did this to get a smoother wind
field and moderate any very low or high wind speeds. For the rest
of the long range utilized WPC for its use of ensembles. Forecast
confidence is below average.
.AVIATION...Mainly MVFR conditions with low moving onshore across
the central area this evening. This will continue for most central
and south TAF sites into early Fri morning. Should improve to VFR
during late Fri morning to early afternoon. For PAYA, trapped low
level moisture will keep MVFR conditions going through the night
with potential for IFR late tonight as trof moves in. They may
improve to VFR Fri afternoon but for now keeping MVFR ceilings as
that will depend on how much of a break in cloud cover occurs to
allow heating to raise cloud bases.
MARINE...Gale Warning for PKZ042.
Small Craft Advisory for PKZ022-031>036-041-043.
Small Craft Advisory due to Seas for PKZ051.
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