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

fxus66 kpqr 200424

Area Forecast Discussion
National Weather Service Portland, OR or
917 pm pdt thu sep 19 2019

.synopsis...a series of storm systems will bring alternating days of
dry and wet weather through at least early next week with saturday
and monday shaping up to be the driest days.


.short term...tonight through sunday...water vapor satellite imagery
reveals the large shortwave trough that brought the unsettled weather
of the past several days slowly working its way eastward across the
great basin. a shortwave ridge is also readily apparent over the
northeast pacific. this has placed the region under large scale
northwesterly flow aloft. a mini-shortwave trough can be seen sliding
southeastward across british columbia. mid level positive theta-e
advection in advance of this feature is resulting in a broad area of
mid level clouds dropping southward. enough lift over a deep enough
layer is beginning to result in sprinkles reaching the surface per
krtx radar and surface observations across northwest oregon and
southwest washington. have increased pops accordingly for tonight
even though most locations will likely not measure despite many
people likely seeing at least some rain drops falling from the sky

some shallow low level instability will also spread southeastward
across the area friday. this should be enough for at least a
few light showers to spread onto our coast late tonight and then
inland across southwest washington on friday. the sref does have a
few members that keep places like kast dry on friday so have gone
with a blend of the nbm and sref pop forecast for friday, but it
should be noted that every member of the gefs and ecs systems produce
measurable qpf so our 60-70% chance of rain may still be selling rain
odds a bit short. it appears rain chances decrease rather markedly
between multnomah/clark and lane/benton counties on friday so while
eugene and corvallis could see rain on friday, it certainly appears
more likely that places like portland and vancouver will see at least
some light rain on friday.

shortwave ridging still looks on track to transition eastward across
the area friday night into early saturday. this should result in
most, if not all, showers ending during this time. there should be
enough sunshine or at least filtered sunshine to allow inland valley
temperatures to warm to near 70f on saturday. the next storm system
still appears on track to bring another round of rain on sunday, but
nothing that`s too out of the ordinary. precipitation will turn more
showery sunday afternoon with perhaps a short lived thunderstorm or
two possible somewhere in the cwa. /neuman

.long term...sunday night through wednesday...a front along the
leading edge of a long wave trough will move over the pacific
northwest on sunday. this system will bring an ample amount of rain
to the area through early monday morning. however, the rain is
expected to be fairly short lived as it exits the area monday. as
the front leaves, a ridge will build in behind it as high pressure
develops in the pacific. as is common with a ridging pattern, skies
will begin to clear slightly, allowing overnight temperatures to
decrease. lowering temperatures in combination with residual
moisture from the rain on sunday will create a threat of fog through
the willamette valley, along the coast and low lying lands through
the coastal range. otherwise, monday should remain dry and
relatively clear.

one challenge with the long term forecast lies in how the
numerical models are handling the ridge. in previous runs it has
been more amplified leading to clearer, drier and warmer weather.
however in more recent runs, several disturbances over canada have
begun to shift southward causing the ridge to flatten. the
flattening will increase a chance of several shortwaves passing
through the ridge and bringing spouts of rain on tuesday and
wednesday. -muessle


.aviation...expect mostly vfr conditions through early tonight,
with a weak front spreading lower vfr to mvfr ceilings across
most of the region, starting with the northern coastal areas
around 05z. this mvfr cloud deck should be the dominant impact
overnight, though cannot rule out the potential for local ifr
conditions especially along the coastal area. mvfr conditions
are likely to persist through at least 19z for most locations,
possibly lingering into the afternoon in some spots.

kpdx and approaches...vfr conditions to persist through the early
evening hours, but ceilings in mvfr category become likely again
later tonight between 06z and 10z. expect mvfr ceilings to
persist well into friday, with a chance of improvement to vfr
category after 19-21z.


.marine...surface high pressure offshore will keep a modest
northwest breeze going into saturday night, generally in the range
of 10 to 15 kt. gusts thursday evening may reach 20 kt across the
southern waters. a cold front sunday will bring a turn to southerly
winds gusting to about 20 kt as it passes through. winds then return
to the northwest, and are expected to increase into small craft
advisory range with gusts up to 25 kt sunday night. weaker winds are
then expected again monday and tuesday.

the northwest swell of 6 to 7 ft thursday evening will slowly
subside into the 4 to 5 ft range by the end of friday. the cold
front sunday will drive combined seas up to 9 to 10 ft sunday and
sunday night.


.pqr watches/warnings/advisories...



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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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