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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
644 pm pst mon feb 17 2020


.synopsis...high pressure will build over the pacific northwest and
result in a dry work week. the next storm system will bring valley
rain and mountain snow next weekend.


&&

.update...issued a quick update to the zones/grids to accommodate a
few pesky showers lingering into the evening hours. these should
dissipate by 9 pm, as surface temperatures cool. otherwise, the
forecast looks on track, so made no other changes. with temperatures
expected to fall below freezing across most of the region, areas
where roads remain wet from this weekend`s precipitation may have
black ice issues later tonight into tuesday morning`s commute.
weagle

.short term...today through thursday...water vapor satellite imagery
reveals a shortwave trough sliding southeastward into the northern
great basin this afternoon. shallow instability under low to mid
level northwesterly flow has allowed a few showers to persist near
the coast and across the higher terrain. daytime heating has also
allowed some of this shallow instability to be realized across the
lower columbia and northern willamette valleys and adjacent foothills
of the coast range and cascade where a few light showers are
beginning to pop per krtx radar imagery. expect all showers to come
to an end rather quickly this evening as daytime heating wanes under
building 500mb heights. given nights remain plenty long and there is
no shortage of low level moisture, expect areas of valley fog and low
clouds to develop tonight.

a barely discernible shortwave trough near haida gwaii early this
afternoon will dive southward over the next 24 hours as a shortwave
ridge offshore amplifies. this will result in our flow turning
increasingly northerly to even northeasterly across northwest oregon
and southwest washington late tonight and tuesday. this should result
in any fog and low cloud development to decrease rather quickly on
tuesday except across the southern half of the willamette valley
where it will upslope and likely persist into at least part of
tuesday afternoon. as a result, did bump tuesday`s high temperatures
down a few degrees in the southern willamette valley.

our flow will turn even more easterly tuesday night into wednesday
under a lowering subsidence inversion as shortwave ridging moves
overhead. this should result in northerly winds in the willamette
valley decreasing tuesday night and easterly winds picking up through
the columbia river gorge and across the cascade ridgetops. given the
time of the year, this isn`t a huge deal, but did hold maxrhs well
below nbm guidance across the higher terrain during this period. any
fog development should be very limited in nature and primarily
confined to the lower columbia river valley around kelso/longview and
the far southern willamette valley around springfield/creswell.
cooler air will reside east of the cascades during this event so this
won`t be a warm east wind event, but most valley locations should
still warm well into the 50s on wednesday and would not be surprised
to see a few locations in the north-central willamette valley and
along the coast get close to 60f.

models are in good agreement a shortwave trough will press eastward
towards the region late wednesday and thursday. there remains good
agreement that it will split enough that a front will largely die
before reaching the area. as a result, only expecting an increase in
mid and high level clouds on thursday with valley high temperatures
climbing back into the 50s again. /neuman


.long term...thursday night through monday...models hint that a
weakening front will approach the region late friday as a shortwave
trough slides eastward into british columbia. at this point, model
and ensemble guidance has trended towards a weaker scenario, which
more than likely results in the entire cwa remaining dry through
friday. did hold onto some slight chance to low end chance pops for
our far northwestern zones on friday as cannot completely rule out
rain yet.

models and their ensembles remain in good agreement a more
consolidated shortwave trough will drop southeastward into the
pacific northwest late saturday into sunday. this storm system
appears likely to bring another shot of valley rain and mountain snow
during this period. while snow levels will likely begin above the
cascade passes, it appears they will likely lower down into the
1000-2000 ft range by late sunday. it appears precipitation will
likely turn showery late sunday into monday with precipitation
chances decreasing steadily during this time. /neuman


&&

.aviation...generally vfr across the most of the area early this
afternoon. main exception is the cascades and foothills where areas
of mvfr are occurring. cyclonic northwest flow aloft associated with
a departing trough will result in isolated shower activity through
early evening, especially over the north oregon coast range and
cascades as well as the willapa hills and south washington cascades
and foothills. brief mvfr conditions can be expected with these
showers, otherwise vfr to prevail. skies clear this evening, but
local lifr or worse will be likely after 06z tue. light offshore low-
level flow develops tue morning and then strengthens in the
afternoon. any ifr or lower conditions tue morning should be gone by
18z.

kpdx and approaches...vfr conditions to prevail through tue morning.
there is a 10-20 percent chance of showers at the terminal this
afternoon through early evening, but a slightly higher chance toward
the cascade foothills. skies clear after 04z tue. there is the
potential for lifr or worse conditions to develop in the tualatin
river valley after 06z. there is also a chance ifr/lifr stratus or
fog may creep down the columbia to the terminal just before sunrise.
should this occur, it should dissipate between 15z and 18z. weishaar

&&

.marine...north wind prevails over the waters today. thermally-
induced low pres along the north california coast today will expand
north tonight and tue. this will result in 20 kt gusts over the
pzz255 and pzz275. there is the potential for 25 kt gusts south of
heceta head, but feel the gusts will be isolated. offshore flow
develops late tue and continues through wed. latest model runs
indicate the possibility of 25 kt gusts tue night through wed
morning near the coastal terrain gaps and extending into the outer
waters across pzz270.

surface gradients relax wed night through fri, with wind speeds
generally 10 kt or less. wind speeds increase sat due to an
approaching frontal system. 12z operational runs in good agreement
showing small craft advisory level wind speeds starting late sat.
gusts to 35 kt may be possible sun.

seas will hover around 8 to 9 ft today and then lower to 5 ft by the
middle of the week. guidance shows seas building to near 10 ft sat.
enp and its spectral guidance suggests seas will get close to 25 ft
sun. these seas appear to be generated by a sub-985 mb low near 51n
132w sat evening, according to the gfs.
enp guidance shows a 35-ft bullseye north of buoy 46005 12z sun.
model decays this to 25 ft over the south washington and north
oregon waters sun afternoon. the ecmwf wave model is more
conservative, depicting 15-20 ft seas sat night through sun morning.
the 12z ecmwf is weaker and much faster with the weekend surface
low. have hedged toward the higher enp wave heights for now, but
would not be surprised if subsequent gfs runs started to trend
toward the ecmwf. weishaar

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...none.

&&


$$

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

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