Gale Warning 160, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
240 PM AKDT Sun May 21 2017

.SHORT TERM.../Through Monday night/Occluded front is moving
across the northern Panhandle late this afternoon. The front will
stall across the southern Panhandle tonight and stay there Mon as
weak low pressure waves move NE along the front. The front should
move E of the area by late Mon night. A weak low will move NE into
the far S gulf by Mon evening, then move E into the SE gulf by
late Mon night. Did not make a lot of changes to the forecast,
except did blend in 15z SREF for POPs and used latest RFC for QPF.

Main forecast concerns will be precip potential/amounts and winds.
Precip is diminishing behind the front along the central coast and
this trend will move inland to the N panhandle early tonight.
However, enough low level moisture and increasing instability will
allow showers to develop and move in a few hours after the front
moves by over the N half of the area. Will see a gradual
diminishing trend in the showers over the far N panhandle late
tonight into Mon. Over the S half...with front hanging up and low
pressure waves moving in, rain will continue over that area and
could be locally heavy especially in zone 28. Once the front moves
E of the area later Mon night, precip will become showery. Over
the NE gulf coast, showers will move onshore around a low over the
NW gulf, but they will gradually diminish later tonight and Mon as
low moves away and weakens. The low moving NE into the S gulf Mon
then E into the SE gulf Mon night will increase showers over the
S half of the gulf, and these will spread E into the S and central
panhandle late Mon afternoon and evening. Rainfall amounts will be
locally heavy over the S where another 1 to 3 inches is likely by
late Mon night. Over the rest of the area, less than an inch of
additional rain is expected through Mon night.

Winds over the area increased with the front moving through, with
most areas around 20-30 KT over the N and central panhandle. The
winds will decrease over the central area gradually tonight to
10-15 KT, then remain there for Mon, before diminishing further
Mon night. Over the S, with front hanging up, winds will stay up
more but they will gradually diminish as well, with 25-30 KT
dropping to 15-20 KT by late tonight, then down to 10-15 KT Mon
night after front moves E of them. Over the gulf, strongest winds
will be over the N gulf near the low over the NW gulf, with 25-30
KT winds likely to start, but they should gradually drop off to
10-20 Kt by late tonight as low moves away and weakens. Will allow
the strong wind headlines for zones 17 and 25 to expire at 4 pm
this afternoon.

.LONG TERM.../Tuesday through Sunday/as of 10 pm
Saturday...Tuesday begins with the last of the precipitation
associated with the string of low pressure systems affecting
Southeast Alaska ending over the southern panhandle. The northern
panhandle should have dried out by this point. Behind this system
a surface high pressure builds. This weather pattern shift will
bring drier conditions and clearer skies. Daytime winds will be
primarily thermally (sea breeze) driven through the extended
forecast. Models have intensified the pressure gradient associated
with the high pressure leading to a slight increase in winds over
the gulf. Small craft level winds are possible over the gulf from
south of Chichagof Island to Haida Gwaii late Tuesday through
Wednesday.

Temperatures are expected to warm later this week with 850
temperatures above 10 C over much of the panhandle going into the
weekend. A return to the upper 60s and possibly even low 70s is
possible toward the end of the extended forecast.

Model agreement is above average in the long term. A blend of the
ECMWF and GFS was primarily used taking some input from WPC later
in the extended forecast.

&&

.AVIATION...Plentiful reports of LLWS and turbulence across the
panhandle today (mainly from Cape Fairweather southward) as a
strong front moves through the area. Vis and Ceilings have also
been low with mostly MVFR with occasional IFR as the heaviest
rain bands moved through. Conditions are starting to improving
north of Cape Decision as the heaviest rain has moved into Canada.
Kept at least MVFR conditions with some gusty winds through the
night then showing more noticeable improvements tomorrow. For the
south, substantial rain continues. Some improvement expected to
MVFR later tonight but conditions will deteriorate again early
Monday as the next frontal wave brings even more rain. Winds are
expected to remain on a diminishing trend through the period
though.

&&

.HYDROLOGY...Many area small streams and rivers came up 1 to 3
feet in the past 18 hours, but none of them are at bankfull levels
and should remain below that level through Mon. Small rivers and
streams over the N will likely peak tonight and drop off Mon and
Mon night as precip diminishes. Larger rivers will likely continue
rising through Mon in response to the precip that has fallen
already, but they should level off Mon night. Over the S, small
streams and rivers should rise through Mon with the locally heavy
rain, then level off Mon night as rain rates drop off. Larger
rivers may rise through Mon night though. Not expecting any of
them to reach bankfull levels at this time.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 4 PM AKDT this afternoon for AKZ017-025.
MARINE...Gale Warning for PKZ036-051.
     Small Craft Advisory for PKZ012-013-031>035-041>043-052-053.
     Small Craft Advisory due to Seas for PKZ022.

&&

Byrd/RWT

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