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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
342 am pdt tue aug 16 2022

.synopsis...high pressure across the great basin will expand into our
area through mid week to promote a hot wednesday and thursday, with
more seasonable temperatures likely to return by the upcoming
weekend.
&&

.discussion...

key messages:

* above normal temperatures will occur inland through thursday.
  wednesday and thursday continue to appear the hottest days.

* high heat risk is forecast for much of the population across the
  north and central willamette valley, clark county, and the
  columbia gorge/upper hood river valley on wednesday. moderate heat
  risk is forecast for sensitive groups thursday.

* a thunderstorm threat will exist for the higher oregon cascades
  wednesday evening through thursday evening. there is the
  potential for the thunder threat to expand more to the west
  wednesday night.

detailed discussion (through next monday)...at 3 am, water vapor
satellite shows elevated moisture streaming northeastward along the
pacnw coastline and into the olympics, indicating a weak shortwave
trough which deterministic guidance suggests will pass to our north
through the morning. in its wake, ridging will build in from the
great basin to bring increasing 500hpa heights and resultant warming.

today temperatures will be above normal for the interior lowlands,
but not significantly so. highs are forecast to peak in the upper 80s
to low 90s, which is only around 6 to 10 degrees above normal for
mid august; for instance, the average high at pdx for august 16th
through the 22nd is 82 degrees. wednesday, we heat up further and
many areas will thus enter the high heat risk category as high
temperatures reach the 95 to 103 range across the interior. nbm is
now giving around an 80% that temperatures will exceed 95 and nearly
a 50% chance that highs will reach the triple digits in salem on
wednesday. thursday looks similarly hot, though uncertainty in the
temperature forecast is greater. the nbm interquartile range (iqr),
or mid-50 range, spans 92 to 102 on thursday in salem, whereas the
range extended from 97 to 102 on wednesday. this indicates the
probability for temperatures at or above 102 is the same (around
25%) on both days, while the likelihood of temperatures at or
greater than 97 is significantly lower on thursday compared to
wednesday (in fact, it drops from ~75% to ~55%). even so, the
chances for setting a record high temperature on thursday currently
appear higher than the chances for doing so on wednesday in the
northern and central willamette valley. see below for record highs
(and their chances of being broken) on both days.

wednesday                   thursday
      pdx: 105 (1%)              pdx:  99 (34%)
    salem: 105 (7%)            salem: 102 (17%)
   eugene:  97 (42%)          eugene:  98 (27%)


much of the spread in thursday`s high temperatures forecast can be
explained by the models` spread in whether and where convection will
occur wednesday evening/night. forecast soundings from the nam
continue to suggest ample elevated instability across the entire
area, though strong capping will make it difficult for convective
initiation without a sufficiently strong trigger - and on this point
models do not agree. the deterministic ec, gfs, and cmc each show an
area of enhanced, mid-level cyclonic vorticity racing
north-northwestward across nw oregon wednesday evening, but the
strength of the feature is just not nailed down. the nam shows a weak
pv1.5 signature, and in fact suggests a more well defined
tropospheric fold with the parent trough thursday evening; not
surprisingly, the namnest suggests little convective activity
wednesday. meanwhile, the hrrr portrays a few blobs of higher
reflectivities spreading from the cascades across the willamette
valley, as does the high resolution fv3. for now, we`ll keep the
thunder mention in the lane co. cascades on wednesday, as that is
where the nbm and sref have the highest probabilities for thunder (at
around 20%) and where the ec deterministic depicts lightning
activity. we`ll choose to believe the bulk of the ensemble guidance
which keeps the remainder of the area qpfless.

thursday, a westerly component is added to the flow as a negatively
tilted trough approaches our area from the northwest. models still
do not agree on how late in the day this will happen, though. the
gfs keeps southeasterly 700mb flow over nw oregon through mid
afternoon, which could promote convective activity across the
cascades, foothills, and even willamette valley if convective
initiation occurs early enough in the day (or it`s continuing from
wednesday night). however, the ec and cmc steer the flow back to
westerly a little sooner, which would imply convection that develops
in the cascades would be driven quickly east of the crest. this
seems like the more likely scenario, but again it will bear
watching. since thunder chances were highest (approaching 25% in
spots) along the high cascades according to both the sref and nbm,
the slight chance mention in the forecast is confined to that area.

with the arrival of the aforementioned upper trough friday morning, a
strong marine push is expected, and this may ultimately cool
temperatures even more than what guidance currently suggests. the nbm
is giving highs in the mid 80s across most of the interior lowlands,
but one would not be surprised if it ends up even cooler if marine
stratus holds on into the early afternoon. either way, it will feel
much better than wednesday and thursday for those who don`t enjoy the
heat. temperatures look to remain near to slightly above normal
through the weekend as the area remains under southwest flow between
the great basin high and a large trough over the eastern pacific.
-bumgardner

&&

.aviation...12z tafs: typical summer pattern, as high pressure
sits offshore with moderate northerly flow across region. gusts 20
to 25 kt along the coast for the afternoon and evening. air mass
remains stable, with just occasional thin high clouds. do have
shallow marine layer, with ifr stratus along the coast punching
well into the valleys of the willapas and coast range. some
ifr/low mvfr stratus along the lower columbia river and cowlitz
valley as well, with this stratus around the portland/vancouver
metro til 17z. all stratus will break up and dissipate by 18z
inland, and by 20z along the coast.

sidenote: expect pockets of smoke to continue south and east of
albany, mostly due to the fires in upper mckenzie valley.

for detailed pac nw aviation weather information, go online to:
https://weather.gov/zse

kpdx and approaches...vfr with variable high clouds today. marine
stratus, with cigs 800 to 1200 ft, will continue to form over
clark county through 13z, and spread over the east part of metro.
think pdx stays with scattered to broken clouds, but more broken to
overcast as move to east and north of field. this stratus will
dissipate through 17z.                               /rockey
&&

.marine...high pressure will remain anchored offshore over the
next several days, with thermal low pressure along the south
oregon coast into northwest california. this will maintain
moderate northerly pressure gradients over the south oregon
coastal waters, resulting in a prolonged period of northerly
winds over the coastal waters. northerly winds will be strongest
during the mid to late afternoon and evening hours each day,
especially to the south of cascade head. a small craft advisory
is up for the coastal waters this afternoon and evening, but have
extended that through wed evening. gusts 20 to 25 kt expected,
with the gusts strongest and more frequent to south of cascade
head. seas should generally 4 to 6 ft, with the choppiest seas
likely to occur to the south of newport.

not much change thu through sat, through winds will be lighter,
running 10 to 15 kt. seas stay 3 to 6 ft overall.

for information about upcoming marine zone changes, go online to:
https://www.weather.gov/pqr/marinezone

&&

.pqr watches/warnings/advisories...

or...heat advisory from noon wednesday to 10 pm pdt thursday for
     cascade foothills in lane county-cascades in lane county-
     central columbia river gorge-central willamette valley-
     greater portland metro area-lower columbia-northern oregon
     cascade foothills-northern oregon cascades-upper hood river
     valley-western columbia river gorge.

wa...heat advisory from noon wednesday to 10 pm pdt thursday for
     central columbia river gorge-greater vancouver area-i-5
     corridor in cowlitz county-south washington cascade
     foothills-south washington cascades-western columbia river
     gorge.

pz...small craft advisory from 2 pm this afternoon to midnight pdt
     wednesday night for coastal waters from cape shoalwater wa
     to florence or out 60 nm.
&&

$$

www.weather.gov/portland

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