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
930 pm pst thu jan 23 2020

updated short term/aviation/marine sections

.synopsis...a cold front will slowly move across sw washington and nw
oregon tonight. the upper trough moves across the area friday.
unsettled weather continues into next week resulting in more valley
rain and mountain snow. temperatures remain rather mild, with snow
levels remaining mostly above the major passes of the cascades
through the weekend.

&&

.short term...tonight through sunday (updated)...evening water vapor
imagery showed a slow-moving frontal boundary moving onshore. a
vorticity maximum was noted just off the south oregon coast, which
was providing dynamic support for isolated thunderstorms between 03z
and 04z. it also appeared one final wave was riding up the frontal
zone. infra-red imagery indicated a narrow line of enhanced or
colder-topped clouds associated with the vorticity maximum.

in general, decreasing rainfall rates were observed across sw
washington and far nw oregon this evening. at 0440z klgx doppler
radar showed some 40-50 dbz returns along the north oregon coast
associated with the colder-topped clouds. this enhanced cloud top
band appears to be the back edge to the cold front and will move into
the interior valleys overnight. thus, although there may be a short
period of increased rainfall rates for the higher terrain of sw
washington and the north oregon coast range, would expect rain
intensity to diminish overnight. the 00z href guidance shows the
heavier forecast reflectivities to be in the cascades by 10z, with
just scattered shower activity for willapa hills and north oregon
coast range. with all this said, have opted to end the flood watch.

as of 04z the grays river was on a downward trend, having crested
near 15.0 ft around 23z thu. the naselle river crested near bankfull,
while the wilson river was just above flood stage, but below the
forecast crest. although not the classic atmospheric river event,
rainfall in the willapa hills has been rather impressive. huckleberry
raws picked up nearly 6 inches over the past two days.

the 00z nam indicates the upper level trough axis will move across
the forecast area friday morning. snow levels gradually lower to near
the cascade passes by 18z fri. the south washington cascades will
likely pick up 2 to 6 inches friday, but well above any major
roadways. precipitation chances will gradually decrease on friday,
with a mix of sun and clouds. nudged pops lower fri afternoon,
especially for the south portion of the forecast area. another low
pressure area will move across the region to our north friday night
into saturday. at this point this system doesn`t look to be as wet as
today`s front, but most of the area getting another 0.20 to 0.40
inches of rain, with up to an inch in the higher terrain. snow levels
will be rising so not expecting a lot of accumulations in the
cascades below 7000 ft. guidance then shows another surface low
moving across the area saturday night into sunday morning. models
seem to be trending a little weaker with the surface low, but gusts
to 50 mph will be possible sat night for the beaches and headlands.
weishaar

.long term...sunday night through wednesday...a chaotic long term is
expected with a series of shortwave disturbances bringing persistent
valley rain and mountain snow through the end of the forecast
period. ensemble guidance agrees that a weak shortwave will bring
heavy rain to the coast and snow across the cascades as it tracks
across the waters sunday night into monday. there is little
confidence after monday afternoon as sporadic shortwaves create for
challenging solutions in winds and temperature between the models.
there could be a short period tuesday evening where the rain will
lighten but another round of heavy precipitation is expected on
wednesday.-bphillips

&&

.aviation...despite all the rain this evening, conditions are
primarily vfr across the inland terminals. areas of mvfr are
possible in areas of heavier rain until 07z, but coverage of mvfr
should decrease overnight as a cold front slowly moves across the
cascades. southerly winds through the willamette valley are
expected to keep the area well mixed, which should hamper the
development of visibility restrictions through fri morning.
meanwhile, moist onshore flow and rain or drizzle will keep the
coast mvfr along with a few areas of ifr.

we will maintain a mention of llws in the tafs for kpdx and
kttd until 12z, as e-se outflow from the columbia gorge conflict
with 30-40 kt s-sw winds around 1500-2000 ft agl. surface winds
should become more southerly by 12z, lessening shear as winds
aloft decrease as well.

kpdx and approaches...mainly vfr conditions with occasional bouts
of mvfr in ra through friday morning. e-se winds near the surface
will combine with s-sw winds aloft for llws until a frontal
system moves through later tonight, turning surface winds more
southerly.  weagle

&&

.marine...an active pattern will persist through the next week
as a series of fronts stemming from the pacific move over the
waters.

there are several embedded lows within the flow of a broad parent
trough, which is located within the gulf of alaska. these weak
lows are creating several different swell trains, resulting in a
very steep and choppy sea state. the westerly swell is the more
dominant and will be consistent through next week. in general,
heights will be around 12 to 15 ft through friday. seas look to
subside to 8 to 10 feet during the weekend, will build back
towards the mid teens again sunday and monday, then subside to 9
to 11 feet starting tuesday.

will need to monitor the sneaker wave threat closely as we head
into the weekend. long-period westerly swell will arrive tonight,
but periods should decrease into the mid-teens by sat morning.
weagle/42


&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...small craft advisory until 6 am pst saturday for coastal waters
     from cape shoalwater wa to florence or out 60 nm.

     small craft advisory until 10 pm pst friday for columbia river
     bar.

&&

$$

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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.