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

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Area Forecast Discussion
national service portland or
925 pm pdt sun jul 21 2019

updated aviation section

.synopsis...an upper level trough will swing across the region
early to midweek and bring cooler temperatures before weak high
pressure returns and brings another warming trend late in the work
week.

&&

.short term...tonight through wednesday...water vapor satellite
imagery this afternoon shows a large and broad shortwave trough over
the northeast pacific. as this upper level storm system approaches
the pacific northwest over the next 48 hours, expect increasingly
south to southwesterly flow aloft to spread across the region. this
should enable more and more marine clouds and cooler temperatures to
gradually infiltrate northwest oregon and southwest washington
through midweek.

in addition, water vapor satellite imagery indicates an elongated
vort max lifting north-northeastward off the coast of california this
afternoon. models are in general agreement the pv anomaly associated
with this feature will lift from klamath/lake counties northeastward
into umatilla/wallowa counties overnight into monday morning. the
northern periphery of this feature will skirt our cascade zones and
coupled with some mid level instability will bring a small threat for
elevated convection to the cascades. given cira currently outlines
0.3" of 700-500mb alpw in an area that will remain east of our cwa,
only expecting an increase in high level clouds and some mid level
altocumulus across our cascades later tonight and monday morning.

a number of the higher resolution models that simulate cloud cover
suggest tonight will be similar to last night in terms of marine
cloud coverage. given last nights model runs under did cloud
coverage, onshore pressure gradients will be higher across the
region tonight and 500mb heights will slowly decrease, thinking the
high resolution models are a bit underdone with regards to marine
cloud coverage so have maintained the current forecast with clouds
filling in along our coast and across the lower columbia river
valley by monday morning.

have also maintained a slight chance of thunderstorms across far
eastern lane county along the cascade crest for late monday afternoon
and early evening, but southwesterly flow aloft should keep the best
chances of a thunderstorm east of our cwa. the sref thunderstorm
probabilities and href guidance also support this general idea.

models still remain in good agreement the aforementioned shortwave
trough over the northeast pacific will sharpen and swing
northeastward across the pacific northwest tuesday night. however,
there are amplitude differences between models. specifically, the gfs
appears to be the major outlier by more directly hitting northwest
oregon and southwest washington with a 500mb vort max and cold pool.
however, it even appears to be an outlier within the gefs ensemble
system. as a result, there is a low chance for some light showers and
drizzle along the coast and across the cascades tuesday night and
wednesday morning, but it does not appear to be nearly as much of a
given as the gfs would seem to suggest.

between a rapid increase in 500mb heights across the region, the
surface high pressure ridge axis shifting well northwest of the cwa
and a developing thermal trough over northern california, our low
level flow should turn increasingly northerly on wednesday. this
should allow clouds to clear a bit faster on wednesday than one might
initially anticipate following a deep marine push. this will likely
be most dramatic across the southern two thirds of our cwa on
wednesday afternoon where it should be mostly sunny by evening.
/neuman

.long term...wednesday night through saturday...guidance continues
to keep the bulk of the energy to our north. this should result in
dry and somewhat seasonable weather across the forecast area with
temperatures in the low to mid 80s inland and mid 60s to around 70
along the coast. will also see periods of late night/morning stratus
along the coast and portions of the interior, generally along the
lower columbia river. otherwise, expect plenty of sun across the
region.  /64

&&

.aviation...vfr conditions continue across most of the region
this evening, with some thin mid-level clouds developing across
the cascade foothills and marine stratus again forming just
offshore and in the coastal valleys near konp and k6s2. this low
mvfr to ifr marine stratus should redevelop toward 08z and
remain through early monday morning. meanwhile, slightly stronger
onshore flow should allow some stratus to reach into the southern
willamette valley around keug and along the lower columbia past
kkls, possibly extending into the metro portland terminals. any
stratus should clear from the interior lowlands by mid-morning,
but perhaps linger along the coast until midday. vfr conditions
generally expected thereafter.

kpdx and approaches...vfr conditions this evening with light n-nw
surface wind. as onshore flow increases overnight, around a 25%
chance of mvfr stratus pushing along the columbia into the
terminal area late tonight.  cullen

&&

.marine...quiet weather with no significant concerns for the next
few days. wednesday afternoon and evening another thermal trough
strengthens along the southern oregon coast. expect winds to nose
above 20 kt. seas generally stay under 5 feet until wednesday
night into thursday when winds bring seas up to around 4 to 6
feet. -mccoy

&&

.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 nautical miles offshore. this area is
commonly referred to as the forecast area.