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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
239 pm pdt mon sep 26 2022

.synopsis...high pressure will bring continued warm and dry weather
through tuesday. then, a pacific frontal system will push inland
wednesday through thursday and bring widespread rain and cooler
temperatures to northwest or and southwest wa. upper level ridging
returns late in the week, resulting in warmer and drier conditions.

&&

.short term...tonight through wednesday night...satellite and surface
weather observations from early monday afternoon depicted clear skies
across all of northwest oregon and southwest washington, aside from
the coast where a persistent low marine stratus deck was holding
strong. the aforementioned marine stratus deck should continue along
the coast through tuesday, and will most likely expand into portions
of the southern and central willamette valley tonight due to a
southwest-to-northeast oriented marine push. decided to use the nbm
90th percentile sky cover guidance for the cloud cover forecast
tonight through tomorrow, which yielded more of an "all or nothing"
cloud cover forecast that is more realistic.

tomorrow looks to be another warm day with plenty of sun aside from
the coast and the southern willamette valley during the morning
hours. although temperatures will remain above normal for late
september, it will not be quite as warm as of late due to falling 500
mb heights/850 mb temperatures ahead of an approaching upper level
trough. the nbm is suggesting highs in the upper 70s over the south
valley to the lower 80s over the north valley, with 60s at the coast.
this seems quite reasonable given cloud cover expectations.

conditions start to change tuesday night into wednesday as the
aforementioned upper trough begins pushing inland, bringing a surface
frontal system with it. nearly every single ensemble member from the
gefs/eps/cmc produce measurable rain across northwest or and
southwest wa, if not a solid wetting rain. in fact, the nbm v4.1 is
showing a 50 to 70 percent chance of at least 0.25 inches of rain
tuesday night through wednesday night for the willamette valley, with
even higher probabilities at the coast and across southwest
washington. decided to use nbm v4.1 for pops with this system, which
bumped pops up across the board and matches our current messaging of
"it will rain, we just don`t know exactly how much yet." this is good
news for those who have been craving fall-like weather with cooler
temperatures and measurable rain! -tk


.long term...thursday through sunday night...an upper level ridge
will push into the pacific northwest thursday night into friday,
bringing the return of warm and dry weather. northwest oregon and
southwest washington will be in between wednesday`s trough and
friday`s ridge on thursday with cool northwest flow aloft. this will
help maintain post-frontal showers on thursday along with cooler
temperatures and highs in the mid 60s to lower 70s across the
lowlands.

wpc`s cluster analysis for 500 mb heights depict good agreement
amongst models and their ensembles in regards to the synoptic-scale
pattern friday through the weekend, suggesting upper level ridging
will result in above normal 500 mb heights. the nbm keeps the area
dry during that time and suggests highs will rise back into the low
to mid 80s for the interior lowlands. this is a good 10 to 15 degrees
above normal for the beginning of october. it appears saturday will
be the warmest day; this is when the nbm 25th to 75th percentile
guidance is generally in the 80s. -tk

&&

.aviation...00z tafs: dry, southwest flow aloft through tonight
with high pressure across the region. expect vfr conditions to
persist inland through tuesday morning. onshore flow in the lower
levels will likely maintain ifr to low mvfr cigs along the coast
through this afternoon. the marine stratus will fill back in
along the coast this evening, with conditions likely deteriorating
to lifr, and then push through the coast range gaps and lower
columbia river overnight. href guidance suggests a 30-50% chance
that low stratus pushes into keug between 12-17z tuesday. most
other inland terminals should remain clear with only a 10-20%
chance of ifr or mvfr conditions developing.

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

kpdx and approaches...vfr through tonight with mostly clear skies.
only a 10-20% chance for low stratus to develop early tue morning.
light northwest winds to around 4-6 kt. /dh

&&

.marine...high pressure across the waters will gradually diminish
as a low pressure system begins to approach the area. light north
winds under 10 kt continue into tuesday morning then shift to the
south by late tuesday morning. southerlies will gradually increase
through tuesday night. expect south winds to peak late tue night
into wed morning with gusts around 25 kt as the leading front
moves across the coastal waters. winds will decrease briefly
behind the front before another round of strong southerlies
develops across the coastal waters by wednesday afternoon. latest
guidance shows the surface low weakening as it moves toward the
north oregon coast through thursday morning.

initially seas will remain in the 4 to 5 ft range through
tuesday. but seas will begin to build in response to the
approaching weather system on wednesday. seas will be primarily
driven by a 10 ft westerly swell at around 12 seconds. but wind
southerly winds waves will make the seas choppy and hazardous,
with seas peaking around 12 ft by wednesday evening. seas should
gradually subside to below 10 ft late thu morning or afternoon.

the new moon will produce stronger tidal currents during the
evening ebb cycles tuesday through friday. those moving in and out
of harbors and crossing coastal bars should use caution and be
aware of any bar restrictions that may be in place. /dh

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

&&

.pqr watches/warnings/advisories...

or...none.
wa...none.
pz...none.

&&

$$

www.weather.gov/portland

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