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National Weather Service Area Forecast Discussion for Seaside, OR USA

fxus66 kpqr 161218

Area Forecast Discussion
National Weather Service Portland, OR or
418 am pst tue jan 16 2018

.synopsis...showers will decrease from south to north today as a low
pressure moves north into the gulf of alaska. another low will
approach the coast tonight and wednesday then stall offshore the
british columbia coast thursday and friday. this low will bring a
rather dry warm front to the area wednesday followed by a moist cold
front wednesday night and thursday. steady showers are expected
thursday and friday with snow levels below the cascade passes.
showers continue this weekend as the low weakens and  moves inland.


.short through friday. the front which brought rain to
the region last night has moved east of the cascades early this
morning. a line of showers currently around 50 miles off of the oregon
coast will bring a burst of showers to the coast and coast range
around sunrise this morning(between 5 and 7 am). showers will
decrease from south to north today as the parent low, currently
located near 54n 144w moves north. most areas will have a break in
the rain late this morning or early this afternoon with the exception
being the sw washington coast and the willapa hills where a chance
for showers continues through the evening.

satellite imagery shows another low just sw of the low mentioned
above. this low will bring a period of active weather tonight through
at least friday as it slowly moves east across the ne pacific. a warm
front will brush by the area late tonight and wednesday morning for a
chance of rain along the coast and for extreme sw washington.
precipitation will be rather light with this system, with most areas
not seeing any rain. the main impact of this front will be the warm
air advection warming temperatures into the upper 50s wednesday
afternoon. this warmer airmass will also raise the snow levels well
above the cascade passes.

a moist cold front will then bring rain to the coast late wednesday
afternoon reaching the cascades wednesday night. the rain will be
heavy at times and may last through thursday morning. rainfall totals
are expected to be between 0.75 to 1.5 inch from wednesday evening
through thursday morning. the highest rainfall amounts will be over
the washington and oregon cascades with the lightest totals expected
for the central and south willamette valley. this front will also
bring a brief burst of gusty winds to the coast wednesday evening
with gusts around 45 mph for the beaches and headlands.

colder air will move in behind the front thursday and snow levels
will lower down to the cascade passes. the low will stall just
offshore the british columbia coast for an extended period of showery
weather. this will provide the opportunity for the snow pack to
rebuild over the cascades. the snow levels will lower down to 2500
-3000 feet thursday night or friday morning. do not expect a dumping
of cascade snow, but an extended period of steady light snow
accumulations with 1 to 4 inches of snow every 6 hours or so thursday
and friday.

the slow moving nature of the low pressure system will generate a
very large ocean swell that will materialize into extremely hazardous
surf along the beaches. this surf coupled with strong high tides may
lead to coastal flooding thursday and friday. ~tj

.long term...friday night through monday...the pac nw will remain
in an active weather pattern through the end of the forecast period.
models show a series of wet frontal systems moving across the
forecast area over the weekend for another round of heavy rain,
strong winds, and cascade snow. however, impacts over the weekend
remain a bit fuzzy at the moment due to distinct differences in
timing, strength and location of the various systems. nonetheless, it
is becoming increasingly likely that the cascades could get several
inches of new snow this weekend. in addition, we could also see sharp
rises on some of the local rivers. showers return monday as the upper
level trough moves across the pac nw. 64/tj

.aviation...mostly vfr conditions across the region, but there
are pockets of mvfr cigs and vsbys as lingering post frontal
showers remain. feel these showers should become minimal after
16z with vfr to prevail for the remainder of the period. gorge
winds will gradually ease today as a warm front approaches and
crosses late tonight. the associated warm frontal rains arrive
late in the period but do not appear to bring cigs below vfr
through 17/12z.

pdx and approaches...vfr will generally prevail for the 24 hour
period. however lingering showers for the next couple hours will
bring potential for cigs aob 040 and possible down to 025. likely
vfr conditions continuing through the period. east winds continue
to ease today. /jbonk


.marine...convective gusts to 30kt this morning are possible but
should move off the waters over the next few hours. winds should
begin backing to more southeast once again as a strong surface
low center deepens to around 960 mb tonight roughly near 45n,
138w this afternoon. the low moves northeast to near haida gwaii
by 5am wednesday. it will send a warm front across the waters
late tonight with a strong trailing cold front late wednesday
afternoon. expect solid gales to push from west to east tomorrow
as the cold front approaches and have upgraded the gale watch to
a warning. the highest spread of model solutions bring outer
waters gusts to the low end storm force range around 50 kt. will
pencil those gusts into the forecast, but am not yet ready to
pull the trigger on a storm warning. post frontal gales should
continue for the outer waters but ease back to sca level speeds
inside of about 30 nm.

seas will run in the lower teens today then build to the upper
teens by mid-day wednesday as the low center builds a potent
dynamic fetch. the highest seas should reach the waters by
daybreak thursday. there is model consensus between the gfs and
ecmwf based wave models that seas will reach 30-33 feet under a
nearly westerly swell. this could present problems along the
shoreline from high surf along with potential for coastal
flooding given the higher run up potential. seas diminish
significantly fri, but will remain at least 15-20 ft into sun.
seas likely to exceed 20 ft again sat night and sun.


.pqr watches/warnings/advisories...
pz...small craft advisory until 2 am pst wednesday for waters from
     cape shoalwater wa to florence or from 10 to 60 nm.

     gale warning from 2 am wednesday to 10 am pst thursday for
     waters from cape shoalwater wa to florence or from 10 to
     60 nm.

     small craft advisory until 10 am pst wednesday for coastal
     waters from cape shoalwater wa to florence or out 10 nm.

     gale warning from 10 am wednesday to 4 am pst thursday for
     coastal waters from cape shoalwater wa to florence or out
     10 nm.

     small craft advisory for rough columbia river bar until 4 am
     pst thursday.


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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

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