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
818 pm pst thu dec 3 2020

update... for evening aviation section.

.synopsis...high pressure expected to maintain mild weather through
friday. columbia gorge gap flow will bring another round of breezy
to windy conditions to the western gorge and portions of the
portland/vancouver metro area through saturday. a weakening front
will move across the area on saturday bringing precipitation through
late saturday night. calm conditions expected sunday before becoming
more active early next week.

&&

.short term...tonight through sunday...a very mature upper low
center is coming inland near haida gwaii. it`s dragging a weakening
and separating front across the area this afternoon. radar has
certainly shown a fair amount of echos but little, if any, is
reaching the ground as the upper portion of the front races eastward
ahead of the surface feature. don`t expect any additional precip to
arrive after late this afternoon and anything between now and then
may end up as glorified sprinkles. the upper ridge will generally
shift westward again to keep conditions dry through saturday.

higher surface pressure east of the cascades will continue to bring
breezy to windy outflow through the western gorge and across
portions of the portland/vancouver metro through saturday. pressure
gradients will increase again later tonight through saturday with
gusts 45-55 mph possible in the most favored areas. at this time, do
not expect winds will reach advisory levels for the east metro aside
from very occasional gusts around 40 mph, especially on saturday.

interior areas which are not seeing the gorge outflow winds, will
continue to see inversions and light winds result in stagnant air
conditions. this includes most interior elevations below 1500 feet
plus the central gorge/upper hood river valley, and portions of the
metro. these conditions may ease later saturday as south winds
increase and better mixing from low level instability occurs ahead
of an approaching upper trough. it`s far from a certain thing,
however, and there is a distinct possibility little improvement will
occur. do have confidence the upper hood river valley and the
central gorge will keep enough offshore influence to limit mixing
and surface winds.

this upper trough is showing signs of splitting as a trailing
shortwave slides south along the western periphery of the trough. it
may have a hard time making the turn around the base of the trough
and then result in a cut-off low forming with the low center
somewhere near or over our area. will go with chance to likely pops
for now, but have below average confidence in the overall scenario.

a couple things remain questionable for the weekend as a result.
first is if sufficient mixing will occur to clear out stagnant air
surrounding the valley. if not, then stagnant conditions may persist
into early next week. second, will there be precip beginning
saturday night over the upper hood river valley as warmer southerly
flow increases aloft. snow levels are currently projected to rise
above 5000 feet. meanwhile, the low level easterly flow will keep
cooler columbia basin air banked up against the cascade east slopes.
saturday night will likely see temperatures in those two areas fall
below freezing. most models bring very light (a few hundredths or
less) precip to that area, while some bring a tenth of an inch or
more. for now, will favor the solution that most models are showing
with the lighter amounts and thus include a slight chance of
freezing rain for later saturday evening through sunday morning.

a high energy west swell will continue sneaker wave conditions
through friday afternoon. the seas will not generate large enough
surf to alarm beach-goers of the potential threat, and sudden
unexpected rises of sea water onto the beaches could catch those
recreating on the beaches off guard. /jbonk

.long term...sunday night through thursday...once the upper
trough or cutoff low depart, ridging extends back across the area
beginning sunday with the region remaining on the northwestern
fringes. by monday night, a shortwave will skirt across southern bc
and northwestern washington potentially bringing some light precip
across our northern areas. don`t expect to see much wind with this
system, but it may be enough instability to lift the inversions and
provide some stagnant air relief, if necessary. thursday brings a
more defined trough across the region but models differ on the
details on how much precip will occur have largely stayed with the
national blend of models through the extended until further clarity
becomes apparent. /jbonk

&&

.aviation...variable mid and high clouds across region this evening.
weakening front offshore will push inland overnight. as such, will
see widespread mvfr cigs along the coast through about 10z, then
skies will gradually clear again. farther inland, vfr with cigs5000
to 7000 ft at lowest for a time. skies will gradually clear later
tonight as front shifts farther inland. but, good chance will see
pockets of ifr stratus/fog, primarily inland after 10z. any such
that forms will persist well into fri am, mainly to south and north
of portland. high pressure building over inland pac nw will bring
increasing east winds later fri am into the afternoon. this will
keep coast vfr on fri, and clearing of any inland low clouds/fog by
early afternoon.

for detailed regional pac nw weather information, go online to:
http://weather.gov/zse

kpdx and approaches...variable mid/high clouds tonight, though trend
will be towards less clouds by daybreak fri. can not rule out some
spotty fog or low clouds between 10z and 15z, but do not think will
see all that much at the field. but, more likely have this
stratus/fog to the north/northwest towards kspb, and to the
south/southwest of the metro area. increasing offshore flow on fri
will maintain vfr, with east winds 10 kt by 18z fri, and 15 to 20 kt
with gusts 30 kt by late afternoon. as usual, winds bit stronger
towards the gorge, where east winds will gust to 45 kt at kttd by
late fri afternoon, possibly as far west as i-205 bridge.  /rockey

&&

.marine...wind speeds decrease tonight and become light and
variable through friday. the offshore gradient strengthens again
late fri and fri night due to stronger higher pressure inland and
lowering pressure over the waters due to an approaching frontal
system. this will likely produce 20 kt gusts tonight into early sat,
especially for areas parallel to coastal terrain gaps. south wind
increases sat with 25-30 kt gusts possible sat afternoon and
evening. high pressure builds behind the front sun. longer range
models maintain some degree of high pressure over the waters through
mid-week, although a couple of weak systems are expected to move
across the area. these should result in sub-advisory wind criteria.
a stronger system looks to impact the waters late in the week.

at 21z buoy observations continue to confirm the presence of a
long period west swell across the waters. dominant periods have
been 17-20 seconds. this swell will slowly subside to around 10
feet tonight then rebuild to around 13 feet friday morning as
another swell train arrives. seas are expected to subside below
10 feet friday night, but wave heights exceed 10 feet again sat
night. longer range models are coming into better agreement
indicating a larger west swell will arrive early next week with
seas building into the upper teens. weishaar/~tj

&&

.pqr watches/warnings/advisories...
or...air stagnation advisory until 7 pm pst tuesday for central
     columbia river gorge-upper hood river valley.

     air stagnation advisory until 10 am pst saturday for cascade
     foothills in lane county-central coast range of western
     oregon-central willamette valley-coast range of northwest
     oregon-greater portland metro area-lower columbia-northern
     oregon cascade foothills-south willamette valley.

wa...air stagnation advisory until 7 pm pst tuesday for central
     columbia river gorge.

     air stagnation advisory until 10 am pst saturday for greater
     vancouver area-i-5 corridor in cowlitz county-south
     washington cascade foothills-willapa hills.

pz...small craft advisory until 4 pm pst friday for coastal waters
     from cape shoalwater wa to florence or out 60 nm.

     small craft advisory until 8 pm pst friday for columbia river
     bar.

&&

$$

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