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

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Area Forecast Discussion...updated
National Weather Service Portland, OR or
922 pm pdt wed oct 18 2017

updated the aviation and marine sections

.synopsis...a series of storm systems will bring periods of valley
rain that may be heavy at times, mountain snow and coastal winds
through the weekend. the first strong, wet front moves through
tonight and thursday. this will be followed by a brief cooler air
mass that will bring snow to the cascades thursday night and friday,
with a chance of thunderstorms elsewhere. another wet strong system
moves through with more heavy rain saturday and sunday.
&&

.short term...tonight through saturday...the first strong frontal
system will be moving through the forecast area tonight and thursday,
stalling inland on thursday as it becomes a bit more north-south
oriented before finally moving east of the forecast area later
thursday and thursday night. the front is producing strong winds
along parts of the coast and the adjacent coastal mountains for a
while tonight, with breezy conditions inland. rainfall rates are not
expected to produce flooding at this point but bear watching. have
trended the qpf upward towards model consensus for tonight and
thursday though.

the associated cooler air mass associated with the parent upper
trough moves onshore thursday night and through the area friday.
this will bring a chance of thunderstorms to the coastal waters
and the coast thursday night, and onshore on friday. snow levels
lower to near pass elevations in the cascades, and advisory amounts
are possible thursday night and friday. the greatest amounts, which
could exceed a foot, would be at ski resort elevations, but the
passes could get close to or exceed 6 inches.

precipitation will briefly taper off friday evening before increasing
later friday night and saturday as heavy rain from strong warm
advection with the next warm front moves in. the models suggest the
heavy rain will initially broadside southwest washington and
northwest oregon late friday night and saturday, before impacting
mainly the northern areas saturday night. the cold front then sweeps
southward through southwest washington and northwest oregon sunday
and sunday night to complete the heavy rain episode.

this second event will produce more rainfall across the area than the
one tonight and thursday, and as a result has greater potential to
produce hydrological problems for our forecast areas, including the
burn scar areas. tolleson

.long term...no changes. previous discussion follows...
saturday night through wednesday....strong moist zonal flow will set
up over the region saturday night through sunday. snow levels will
rise above 8,000 feet. still some uncertainty as to whether or not
the heaviest rain will set up over western oregon or western
washington. have kept pops high, but forecast details such as amount,
intensity, and duration are unclear.

expect to see some rises on area rivers, especially in the coastal
basins, and if the heavy rain sets up over urban areas, some
localized urban flooding issues could develop. also, locations with
significant burn scars should be aware of possible flash flooding and
debris flows.

models are suggesting, short wave ridging will develop over the
pacific nw early next week, which should bring at least a day or two
of dry weather. the euro model suggests a weak front could push into
the region during the middle of next week while the gfs remains dry
and mild. given the uncertainty, have trended pops towards
climatology. bishop
&&

.aviation...mvfr cigs at the coast as the cold front is about to
move south-southeast of kast at this hour. vfr elsewhere,
although cigs are lowering in response to the relatively slow
moving front. conditions expected to go to predominantly mvfr
conditions later tonight after 07z as the cold front pushes rain
inland. mvfr conditions appear to be the most likely flight
category over the interior taf sites through the day thu. along
the coast expect mvfr, and locally ifr conditions to continue
tonight. as a cold front moves onshore thu, improvement to vfr
category expected along the north oregon coast after 12z, while
further south mvfr to ifr conditions are expected to persist
through most of the day. conditions look to improve after 20/02z.
plan for a return to vfr inland with mvfr at the coast.

kpdx and approaches...mainly vfr conditions through 08z tonight,
although there is a chance for seeing some mvfr cigs anytime before
08z. after 08z expect mvfr conditions to become predominant as
rain associated with a cold front moves in. heaviest rain arrives
around the morning push bringing some possibility of ifr
cigs/vsbys, but still feel lower end mvfr is most likely. conds
improve to vfr after 20/02z. /jbonk
&&

.marine...cold front has slid south of the columbia mouth as of
2100 hrs and will continue slowly drifting south and weakening
overnight. winds and the associated wind wave driven seas have
eased back into the 14-15 ft range fairly quickly after having
peaked around 18 ft across the inner north waters where the
coastal jet had strongest influence. southerly gales will
continue tonight south of the cold front. the front is expected
to reach newport around 6 am thu. the coastal jet will be
somewhat weaker across the central oregon coastal waters with
peak gusts 35-40 kt. seas there will also stay closer to 16 ft
tonight owing to the weaker wind waves.

winds will continue dropping ranging 15 to 25 kt behind the
front, which will allow seas to continue toward the lower teens
by daybreak thu morning. a large long period swell will arrive
from the west later in the day thu. that swell will peak between
20 and 23 ft thu evening, then slowly subside fri and fri night.
these wave heights coupled with the long period, have necessitated
a high surf advisory from thu afternoon through fri morning.
additionally, expect particularly hazardous bar conditions along
the length of the coast. another storm system capable of
producing at least gale force wind gusts appears on track for
friday night and saturday. /jbonk
&&

.pqr watches/warnings/advisories...
or...high surf advisory from 1 pm thursday to 10 am pdt friday for
     central oregon coast-north oregon coast.

     high wind warning until 4 am pdt thursday for coast range of
     northwest oregon.

     high wind warning until 11 pm pdt this evening for north oregon
     coast.

wa...high surf advisory from 1 pm thursday to 10 am pdt friday for
     south washington coast.

     high wind warning until 11 pm pdt this evening for willapa
     hills.

pz...gale warning until 11 pm pdt this evening for coastal waters
     from cape shoalwater wa to cascade head or out 10 nm-
     waters from cape shoalwater wa to cascade head or from 10
     to 60 nm.

     gale warning until 5 am pdt thursday for coastal waters from
     cascade head to florence or out 10 nm-waters from cascade
     head to florence or from 10 to 60 nm.

     small craft advisory for rough columbia river bar until 10 am
     pdt friday.

&&

$$

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this discussion is for northwest oregon and southwest washington
from the cascade crest to 60 nautical miles offshore. this area is
commonly referred to as the forecast area.

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