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National Weather Service Area Forecast Discussion for Seaside, OR USA

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Area Forecast Discussion
National Weather Service Portland, OR or
943 am pst wed dec 13 2017

.synopsis...little change to the overall pattern through thursday as
a ridge of high pressure remains over the region with low-level
offshore flow. the next frontal system moves in off the pacific late
thursday night or early friday, bringing a return of onshore flow
and chances for lowland rain and mountain snow.

&&

.short term...today through friday...first visible satellite images
this morning reveal some fog in the southern willamette valley, but
primarily along and east of i-5. will let the freezing fog advisory
run for another hour or so, but will likely be able to expire it
later this morning as the fog clears and temperatures begin to warm
above freezing.

elsewhere, the surface pattern remains quite similar to the past
several days with a strong low-level inversion and an offshore
surface pressure gradients between the dalles and troutdale on the
order of 7 mb. a more or less persistence-based forecast should hold
through thursday, but with offshore winds through the western gorge
strengthening again a bit late wednesday night and thursday. forecast
models suggest the gradient could strengthen to around 10 mb by early
thursday morning. while this is not quite as strong as last weekend
and early this week, this will still bring a return of windy
conditions to these locations.

the long-awaited break down of the ridge still appears on track for
late thursday night into early friday. latest model data continues to
suggest a slowing of the disturbance as it approaches, so have
continued to trend the forecast this direction. time height
cross-sections indicate only a narrow moisture brand near the front.
as this system is the initial one to move into the
longwave ridge, and moisture is less than ideal, will continue to
maintain pops into the chance category or lower. offshore flow
through the gorge is likely to continue right up until the time the
front moves through friday morning. as such, the temperatures around
hood river and in the hood river valley are likely to remain right
around freezing right until the front moves through. while the onset
of precipitation in the hood river area is likely around late morning
or midday, will continue to include a slight chance of freezing rain
as the moisture arrives.   cullen

.long term...no changes. previous discussion follows...friday night
through tuesday. the long term forecast period is marked by lower
than typical confidence in the specific details, given fairly large
disagreements among model guidance. however, there is some consensus
that heights will begin to fall by at least late tuesday as an upper
trough (of varying strengths) drops across the pacific northwest.
therefore, have trended the forecast closer to seasonal norms - both
in terms of temperature and precipitation (lowland rain/mountain
snow).

&&

.aviation...predominantly vfr conditions areawide. high pressure
continues to dominate. stronger offshore flow through the gorge
develops tonight and thu for an increase in easterly winds,
primarily for kpdx and kttd.

pdx and approaches...vfr conditions through 12z thursday. look
for stronger easterly gorge winds to develop. especially, tonight
into thu. /42

&&

.marine...high pressure aloft will bring relatively little change
in the weather through the end of the work week. a couple swells
moving in from the southwest and west will generally result in
seas hovering between 5-10 ft into next week. a relatively weak
front will likely bring an increase in southerly winds over the
weekend. might have small craft advisory conditions towards
friday in the northern oregon and southern washington waters.
will continue to monitor the situation. /42

&&

.pqr watches/warnings/advisories...
or...air stagnation advisory until 2 pm pst thursday for central
     willamette valley-lower columbia-south willamette valley.

     freezing fog advisory until noon pst today for south willamette
     valley.

wa...air stagnation advisory until 2 pm pst thursday for greater
     vancouver area-i-5 corridor in cowlitz county.

pz...small craft advisory for rough columbia river bar until 3 pm
     pst this afternoon.

     small craft advisory for rough columbia river bar from 11 pm
     this evening to 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
commonly referred to as the cwa, or forecast area.

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