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National Weather Service Area Forecast Discussion for Long Beach, WA USA

fxus66 kpqr 120545 aaa

Area Forecast Discussion...update
National Weather Service Portland, OR or
315 pm pst wed dec 11 2019

updated aviation discussion

.synopsis...low level rain and high elevation snow will persist
through thursday, turning to rain and snow showers friday through
the weekend.


.short term...wednesday afternoon through saturday...a warm front
lifted north earlier today with some rain remaining in the area
behind it this afternoon. most areas will see rain briefly become
more showery overnight before the next system arrives. satellite
imagery this afternoon shows a cloud band associated with a
strong cold front located around 128w with cold pool convection
behind it. there hasn`t been much change in the short term
forecast thinking today, so kept the forecast pretty consistent.
it continues to look like we`ll get a significant amount of rain
and high elevation snow over the next 24 hours, but dry antecedent
conditions should mean there`s no river flooding threat.
significant street ponding is likely if any street drains are
clogged, but don`t see an overall threat for urban flooding.

in addition to rainy, thursday also looks windy across the board,
although significant wind impacts aren`t expected. operational
model runs are pretty consistent in showing about a 4 mb gradient
in the willamette valley, which should translate to winds well
below wind advisory criteria, but people are likely to notice that
it`s windy. in the cascades, wind will combine with snow, but
given the wet nature of the snow, don`t think the combo will cause
long lasting significant visibility reductions.

of note to beachgoers, thursday`s surf is likely to bring
hazardous beach conditions in the form of consistently higher than
usual wave run-ups (high surf) and occasional surprising extra
long run- ups (sneaker waves). see the high surf advisory for more

thursday afternoon, behind the front, kept in a slight chance for
thunderstorms along the north or and south wa coasts. lightning
networks have detected some lightning in the cold pool behind the
front (well offshore) this afternoon and models continue to show
favorable instability into thursday evening as the cold pool moves
towards the local area.

also with the cold pool, snow levels in the cascades will fall
late thursday afternoon through friday, settling around 3500 to
4000 ft friday, then dropping further saturday to around 2500 ft.
expect showery conditions as the snow level drops, so while
widespread snow accumulations after friday morning are expected to
be unimpressive, on/off snow will continue through at least
saturday. bowen

.long term...saturday night through wednesday...operational models
seem to be in agreement that an upper level trough will move through
the area saturday night through monday, increasing chances for
precipitation for the forecast area. snow levels during this time
will settle around 2500 ft bringing snow to the cascades. beginning
monday night, operational models are in agreement that an upper
level ridge will develop over the pacific nw until at least tuesday.
this should result in a break from the rainy pattern. however,
uncertainty remains in the duration of this ridging. following this
brief dry period, an active pattern continues for the foreseeable
future starting wednesday. -thaler


.aviation...the front has all but passed allowing for rain to
begin to tapper off. while there will still be periods of heavier
showers dropping visibilities slightly, those should mostly be
concentrated to southwest washington. the next band of
precipitation, associated with a shortwave, is expected to occur
around 14z thu. this precipitation in conjunction with lifting
skies in the post-frontal environment may cause patchy fog to
form causing visibilities and ceilings to drop yet again. this is
expected to occur at or around 12z thu. a rain/fog mix will
persist through around 18z thu when conditions begin to lighten
and the rain moves eastward over the cascades. easterly flow is
expected to begin to diminish and shift onshore causing gusty
winds to come to an end. chance of some remaining strong winds
aloft around 30kt at 1500 ft but llws was left out of tafs.
clearing skies through the day on thu will create an environment
suitable for widespread fog development, especially in prone
areas around the willamette valley. heavy snow is expected above
4,000 ft asl.

kpdx and approaches...vfr conditions deteriorating through the
night to solid mvfr by 09z thu. rain through the night becoming
light at time, but generally showery. winds are beginning to slow
and will continue to turn offshore through thu. a brief period
of fog is possible after 12z thu, but another band of
precipitation may keep that at bay. expect conditions to improve
to vfr after 00z fri through the remainder of the period. -muessle


.marine...previous discussion as follows. winds will ramp-up
today as a strong front from a gulf of alaska low swings across
the waters bringing gale force winds between 40 to 45 kt later
this afternoon through the evening hours. winds will subside but
remain gusty through thursday night which will continue to pose
hazards for small crafts. high pressure builds over the waters
friday which will weaken the winds to 10 kt or lower. there is a
possibility of a weaker front arriving saturday but there is too
much disagreement on the strength of the winds to put much
confidence in the arrival time

there is a general consensus between models that the primary
swell will be between 17 to 19 ft and period between 15 and 17s.
combined wave heights may reach 20 ft in some areas, mainly
offshore. seas will generally stay at or above 10 ft through the
weekend. long period swells pose an increased risk for hazardous
beaches. -bphillips


.pqr watches/warnings/advisories...
or...high surf advisory from 8 am to 6 pm pst thursday for central
     oregon coast-north oregon coast.

     winter storm warning until noon pst friday for northern oregon

     winter storm warning until noon pst friday for cascades in lane

wa...high surf advisory from 8 am to 6 pm pst thursday for south
     washington coast.

     winter storm warning until noon pst friday for south washington

pz...gale warning until 1 am pst thursday for coastal waters from
     cape shoalwater wa to florence or out 60 nm.

     small craft advisory until 1 pm pst thursday for columbia river



Information courtesy of the National Weather Service - NWS Portland...
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