Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 282254
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
254 PM AKDT Fri Apr 28 2017
.SHORT TERM.../Through Sunday/A high pressure ridge over SE AK
will weaken and drift NE tonight. A weak occluded front over the
central gulf will move to the northern gulf tonight, then
dissipate there Sat. A strong low will move NE to Haida Gwaii by
Sat afternoon, then turn E to the central BC coast while weakening
rapidly Sat night. A weak upper trof will move NE across the area
Sun. Used 12z GFS/NAM blend to handle things through Sun.
Main forecast concerns will be precip potential and winds. Showers
going on over the area will diminish tonight as low level flow
becomes more offshore. Rain with strong low will move NE into the
far southern area Sat. Models differ some on how far N the rain
will get. GFS/NAM basically limit it to the southern 3 zones, but
some rain could get into the far S part of 23 and 26 as well. AS
low moves out Sat evening, the rain should diminish over the far
south. For Sun, upper trof moving in may be strong enough for some
spotty rain over the area. Have generally chance POPs to handle
this on Sun.
Winds will be diminishing over the N this evening while
increasing over the S late tonight and Sat. Over the N, 15-20 KT
S-W winds should become fairly light for a bit by late evening,
then turn more N-E around 10-15 KT late tonight. They will
increase a bit more Sat to 15-20 KT over much of the N and central
area. Over the S, as low moves toward them, winds will become more
E-NE and increase to 15-25 KT by late tonight, then to 25-35 KT
Sat with highest winds over the far S parts. Once low moves inland
Sat night, winds should back to N-NW and drop off some. Trough
moving in Sunday may pick winds up a little bit but most areas
should be below SCA levels. Over the N gulf, winds will pick up to
15-25 KT late tonight as weak front moves in, then diminish Sat as
Otherwise, keeping in patchy fog for parts of the area late
tonight with breaks in clouds and diminishing winds. Sat should
see temps rebound to slightly above average with offshore flow
helping with warming especially over the N. Sun should be cooler
again with more onshore flow bringing clouds and spotty precip.
.LONG TERM /Sunday night through Friday/...
As of 10pm Thursday...Early next week a weak ridging pattern will
be in place over the panhandle that persists until an upper level
low pressure over the western Aleutians begins to track eastward.
Models are in fair agreement of this pattern.
Sunday looks like a relatively drier day as the remnants of a
low pressure system begin to dissipate. After this break, models
are trending toward a wetter pattern, for the panhandle as a
whole. Early next week the offshore flow pattern shifts back to
onshore flow. This should keep temperatures slightly cooler. The
largest concern next week is a stronger low that will travel
across the gulf, carrying further precipitation. Models still do
not have a good handle the intensity (though they are trending
toward a stronger low) and the track it will take.
No significant changes were made in the long term due to models
still not having a good handle on the low pressure system next
week. Used a combination of the ECMWF/GFS with input from WPC in
the long term, the Canadian model seemed like an outlier with the
handling of the low pressure.
AVIATION...Widespread showers with MVFR and some IFR ceiling from
this morning has given way to VFR and MVFR ceilings and drier
conditions this afternoon and evening. Aviation weather is
expected to continue to improve overnight with offshore flow
increasing. Included some fog for various areas as low level
moisture is high and light winds prevail. Tomorrow, northern
airports expected to remain VFR. Southern airports will see
increasing possibility of rain with clouds lowering to MVFR by mid
day as low moves toward Haida Gwaii. Did include some minor wind
shear for PAKT and PAKW tomorrow due to some speed and directional
shear at low levels.
MARINE...Gale Warning for PKZ041.
Small Craft Advisory for PKZ012-036-042-052.
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