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

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Area Forecast Discussion...update
National Weather Service Portland, OR or
832 pm pdt thu sep 24 2020

updated aviation and marine discussions

.synopsis...a warm front will brush the north coastal areas late
tonight, then a cold front will move east across the region friday
bringing another round of rain. a cool unstable air mass keeps a
chance of showers going through saturday. there will be a change to
a drier and warmer weather pattern sunday into next week as a light
offshore flow develops.

&&

.short term...tonight through sunday...showers, some with brief
heavy rain, continued thursday afternoon across much of the forecast
area. expect showers to decrease this evening as air mass slowly
stabilizes, but there may not be much of a break between systems as
the next frontal system approaches the coast late tonight from the
west. a warm front from this system is expected to brush mainly the
north coastal areas areas with increasing chances for rain late
tonight and early friday morning, then a cold front quickly follows
friday moving southeast across the forecast area. as with the
previous system wednesday, models show this system tapping into
subtropical moisture from across the pacific, with precipitable
water values in the gfs 12z run peaking between 1.2 and 1.4 inches
along the coast friday morning. coupled with southwest 850 mb winds
into the coast range likely peaking between 45 and 55 kt potentially
brings a period of fairly heavy rain ahead of the front friday, but
perhaps a little weaker than the water vapor transport values seen
wednesday. as the front remains progressive, expect to see the
steadier rain early in the day turning to showers in the afternoon.
south winds will increase along the coast ahead of the front late
tonight, with south gusts likely peaking around 45 mph along the
northern beaches and headlands briefly friday morning. an enhanced
sneaker wave threat continues along the coast through friday as
incoming waves will be dominated by a long period westerly swell.

model soundings show a moist and unstable low level air mass
persisting friday night through saturday night under a westerly flow
aloft. this will keep a threat of showers going through saturday
night before air mass begins to stabilize again sunday with
subsidence caused by upper level ridging. low level flow turns
northerly sunday as well, helping to dry the air mass and start
warming daytime temperatures back to normal.

&&

.long term...sunday night through thursday..models in general
agreement depicting a sharpening upper ridge over the pacific
northwest early next week, and then hanging on to the ridge into the
latter half of the week. a mild, dry, and for the most part light
offshore flow appears likely to persist in the low levels for much
of the week, resulting in warmer than normal daytime temperatures
and seasonably cool nighttime lows. the easterly offshore flow will
likely bring whatever wildfire smoke is available from over the
cascades and just east of the cascades westward into the region,
assuming the fires are still generating smoke.

&&

.aviation...another round of wind and widespread rain is on the
way as our next front begins advancing inland early friday
morning. expect rain to move into the south wa and north or coast
around 09z friday morning and then spreading south and east down
the central or coast and into the coast range between 10-12z.
rain will then quickly spread further inland across the
willamette valley and into the cascades between 12-15z. expect a
steady moderate rain at all taf sites once rain begins, with
pockets of heavy rain and visibilities as low as a mile or two
from time to time. it appears areas north of ksle will have the
best chance for heavier rain.

the aforementioned front will also bring gusty south winds to the
area, with the strongest winds most likely between 14-20z as the
front pushes inland and moves across western oregon and
southwest washington. expect widespread gusts between 25 and 35
kt during that time, decreasing to below 20 kt by 00z saturday
and below 15 kt by 03z. this will also be when the widespread
stratiform rain begins to transition to scattered light showers,
which will likely linger through friday night and into saturday.
it is also worth noting that llws is also a concern along the
coast into the coast range, as winds aloft will ramp up to 45 to
55 kt around 1500 to 2000 ft. further inland, weaker wind shear
will be possible. therefore have decided to exclude llws from the
inland taf sites as it does not appear to be strong enough.

otherwise, expect mvfr cigs along the coast to start the 06z taf
period with vfr cigs inland. cigs will eventually lower to mvfr
inland as the front moves through, between approximately 12-15z
friday morning.

refer to http://weather.gov/zse for detailed regional aviation
weather and hazard information.

kpdx and approaches...expect southerly winds to begin increasing
between 12-14z friday morning, peaking between 16-20z friday as
a front moves across the willamette valley. gusts to around 25 kt
are anticipated during that time, with a few gusts possibly
approaching 30 kt. in addition, a steady moderate rain will begin
shortly after 12z friday morning and linger through roughly 23z
before precipitation transitions to scattered showers. brief
periods of heavy rain will be possible, with visibility
reductions to around a mile or two. -tk

&&

.marine...another front stemming from the gulf of alaska will
move across the waters tonight and bring another round of gale
force winds and increasing seas. southerly winds will begin to
increase over the northern waters first, beginning around 06z
friday. south winds will then ramp up over the central waters
around 09z. winds will be the strongest during the frontal
passage friday morning, between 12-18z. this is when widespread
gusts to 35 kt are expected, with a few gusts possibly
approaching 40 kt over the northern waters. increasing southerly wind
waves combined with a pesky westerly swell will create hazardous
seas, with significant wave heights peaking between 15 and 18 ft.
therefore, a gale warning is in effect for the northern waters
from 09-18z friday and from 12-21z for the central waters.

winds will rapidly decrease from north to south friday afternoon
and evening, most likely falling below 20 kt by 00z saturday.
seas will also improve and fall below 10 ft by saturday morning
as high pressure begins to build in. conditions will then remain
steady into early next week as the high pressure only builds
further north. there is a chance for some stronger northerly
winds on monday as thermally induced low pressure develops near
the california-oregon border, but there is still model
uncertainty at this time. -tk/muessle

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...small craft advisory until 2 am pdt friday for coastal waters
     from cape shoalwater wa to cascade head or out 60 nm.

     gale warning from 2 am to 11 am pdt friday for coastal waters
     from cape shoalwater wa to cascade head or out 60 nm.

     small craft advisory until 5 am pdt friday for coastal waters
     from cascade head or to florence or out 60 nm.

     gale warning from 5 am to 2 pm pdt friday for coastal waters
     from cascade head or to florence or out 60 nm.

     small craft advisory until 11 am pdt saturday for columbia
     river bar.

&&

$$


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