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

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Area Forecast Discussion
National Weather Service Portland, OR or
200 pm pst tue feb 18 2020

.synopsis...high pressure will keep the region dry through friday.
offshore flow strengthens tonight and wednesday and then weakens
wednesday night and thursday. a weak weather system brushes the
region early saturday, followed by a stronger disturbance sunday and
monday.
&&

.short term...tonight through friday...tranquil weather pattern will
persist through the short term. early afternoon water vapor imagery
revealed a 500 mb ridge over the eastern pacific. the water vapor
looper clearly showed mid and upper level subsidence within the ridge
as evidenced by the dark color pattern. meanwhile, a deep 500 mb
trough could be seen in the gulf of alaska. at 21z visible satellite
imagery the last vestiges of stratus around keug.

offshore low-level gradients continue to strengthen this afternoon.
at 21z the kttd-kdls gradient was -3.5 mb. east wind gusts up to 40
mph have been observed at crown point and 20-25 mph in the higher
terrain of the north oregon coast range. the gradient is expected to
peak around -7 mb 12z wed and then hover around -5 to -6 mb through
the day. model soundings and various time-height sections show
extremely dry air aloft tonight through early thu. expecting much
less fog/stratus coverage tonight and wed morning compared to this
morning. the offshore gradient weakens thu as a weak weather system
approaches the coast. the nam shows the kttd-kdls gradient easing to
near -3 mb thu afternoon and then -1 to -2 mb thu night. the
aforementioned weather disturbance falls apart late thu night and fri
morning as it moves inland. strong subsidence inversions will
continue the next couple of nights. this will lead to poor to
moderate humidity recovery on mid/upper slopes and ridges.
fortunately, the area is far removed from fire season. weak onshore
low-level flow develops fri afternoon. the nam hints at the
possibility of marine stratus pushing into the south washington and
far north oregon coast and coastal valleys late fri afternoon.
weishaar

.long term...friday night through tuesday...models continue to hint
that a weakening front will move across the area friday night as a
shortwave trough slides east into british columbia. the 12z
operational model runs show light qpf across the northern two-thirds
of the area late friday night through sat morning. nearly all of the
ecmwf kpdx ensemble members show no qpf in the 06z-18z sat time
frame. models and their ensembles remain in good agreement showing a
more consolidated shortwave trough dropping southeast into the
pacific northwest late saturday into sunday. there are rather
substantial differences between the gfs and ecmwf regarding this
system. the operational gfs depicts a near 980 mb low at 48n 131w 06z
sun, while the ecmwf is 5-6 degrees longitude more west. this storm
system looks to bring another shot of valley rain and mountain snow
in the sat night through early mon period. the national blend of
models (nbm) shows snow levels lowering to 1000 to 1500 ft sun
evening. however, by sun night the bulk of the precipitation will
have already occurred. the oregon coast range, sw washington willapa
hills and even the higher parts of the pdx west hills may get a
little snow sun night into mon morning. high pressure returns mon
night and tue for a return to drier conditions. weishaar
&&

.aviation...the last low stratus cloud is over keug, otherwise
all sites are vfr and will continue through this evening. high
pressure aloft coupled with a thermal trough at the surface will
continue vfr conditions with offshore flow across the area
throughout the day. east winds across the boundary layer will set
up as a thermally-induced low over northern california builds
throughout the day. there is a possibility of gusty conditions
later this evening as gradients tighten across the cascade range.

kpdx and approaches...the east winds and vfr trend will continue
through the evening and into tomorrow. gusty conditions in kttd
after 10z as gradients tighten over the cascades. -bphillips

&&

.marine...offshore winds prevail over the waters through today.
a thermally-induced low over northern californa will result in
marginal sca gusts over the pzz275 and pzz270. localized regions
of sca gusts will continue through the night and into wednesday
morning as winds push through gaps in the coastal terrain. there
is not enough confidence to issue a wide spread advisory past
10pm this evening as these winds are again marginal and highly
localized. small crafts near heceta head, newport, neskowin,
oceanside and astoria should be cautious tonight and wednesday
morning.

winds will subside wednesday night and begin the transition back
to a westerly regime by friday morning. winds will stay below 10
kt through friday night ahead of a system that looks to arrive
saturday night.

seas will trend between 5 to 8 ft through friday afternoon. seas
will build as the fresh swell from the saturday system moves into
the waters. there is moderate probability of the seas building
to near 20 ft sunday afternoon according to the 12z gwes. -bphillips

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...small craft advisory until 10 pm pst this evening for coastal
     waters from cape shoalwater wa to florence or from 10 to
     60 nm.

&&

$$

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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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