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National Weather Service Area Forecast Discussion for Seaside, OR USA

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fxus66 kpqr 222042
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Area Forecast Discussion
National Weather Service Portland, OR or
142 pm pdt mon may 22 2017

.synopsis...onshore winds will increase this evening as an upper
level trough approaches, for cooler temperatures on tuesday. more
cooling is expected wednesday as the upper trough moves over the
area. expect more clouds with possibly morning drizzle and afternoon
mountain showers wednesday and thursday. high pressure returns friday
for drier, sunnier and warmer weather which will persist through the
holiday weekend.

&&

.short term...today through thursday...winds along the coast have
turned onshore early this afternoon as a thermal trough is slowly
making its way further inland. the thermal trough is over the coast
range early this afternoon and will move across the willamette valley
late this afternoon before settling in over the cascades for the
night. the return of onshore winds will result in a greater marine
influence to the area and cooler temperatures for tuesday. inland
temperatures for tuesday afternoon will be around 10 degrees cooler
than what is expected for today, but will still be around 10 degrees
above the seasonal normal. the coast and coast range will see much
greater cooling tuesday with the afternoon temperatures peaking 15 to
20 degrees below the 24 hour previous temperatures.

an approaching upper trough will flatten the upper ridge tuesday then
move across the area tuesday night through thursday. the marine layer
will deepen tuesday night allowing a further inland reach to the
marine air. marine stratus will likely return to the coast tuesday
night, and push in through the coastal valleys into parts of the
willamette valley (mainly north and central) early wednesday morning.


the marine layer may be deep enough for some drizzle north of salem
wednesday morning. an upper short wave moving over the area in the
afternoon will provide enough lift to possibly produce showers over
the higher terrain in the afternoon and evening. the cloudier skies
and a cooler airmass will result in near to slightly below normal
temperatures wednesday afternoon.

there will be little change in the weather on wednesday night and
thursday as two additional shortwave troughs move over the area.
expect another round of marine stratus on the coast at night pushing
inland in the morning. drizle inland is less likely on thursday, but
mountain showers are still a possibility. the airmass warms slightly
thursday as upper level heights try to build, and the inland
temperatures may warm into the low 70s, but the coastal temperatures
will remain near 60. ~tj

.long term...thursday night through monday. high pressure builds
thursday night and friday and holds over the area through monday.
temperatures will warm into the mid to upper 70s on friday then to
the low 80s for the holiday weekend. a low moving across southern
california will maintain a weak surface pressure gradient across nw
oregon and sw washington and prevent a strong thermal trough from
developing. this will result in light winds that are diurnal and
terrain driven allowing some marine influence in the afternoons and
nights, which will prevent the temperatures from getting excessively
hot. ~tj

&&

.aviation...vfr with increasing very high clouds for the next 24
hours. the coast, however, will likely see lifr fog/stratus
developing after 23/08z and continuing through 23/18-20z as
winds start turning persistently onshore. coastal seabreeze will
also bring gusts 20-25 kt through this evening.

kpdx and approaches...no impacts to vfr approaches the next 24
hours. /jbonk

&&

.marine...high pressure over the nepac will combine with thermal
low pressure inland to bring sca wind gusts to the waters for
the next several hours.

a cold front is expected to drop southeast reaching the northern
waters by tue afternoon. this will result in an increased nw
wind, but still at small craft advisory speeds. expect wind
speeds to diminish late wednesday, however, it may be until
thursday night before gusts fall below 21 kts across all of the
waters. longer range guidance shows lighter wind speeds
thereafter through the early next week.

no significant swell trains crossing through the waters which
leaves seas primarily wind wave driven. exception may be for
several hours tuesday night and wednesday where fresh swell may
build combined seas above 10 ft. there is some uncertainty but
a seas may remain steep enough under short periods to justify an
advisory for square seas beginning tuesday evening lasting well
into thursday. /jbonk

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...small craft advisory for winds until 5 pm pdt wednesday for
     coastal waters from cape shoalwater wa to florence or out
     60 nm.
&&
$$

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this discussion is for northwest oregon and southwest washington
from the cascade crest to 60 nautical miles offshore. the area is
commonly referred to as the forecast area.

Information courtesy of the National Weather Service - NWS Portland...
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