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Area forecast discussion 
National Weather Service Portland or
934 am PDT Thursday Sep 18 2014

Synopsis...low pressure over the California coast will maintain
cool cloudy and showery weather over northwest Oregon today. Drier
weather should be on tap for tonight and Friday as high pressure
begins building into the region. Offshore flow will bring warm
temperatures over the weekend. Cooler unsettled weather may return
towards the middle of next week.


Update...Doppler radar indicates a southwest to northeast
oriented band of light rain is falling across the northern half of
the Willamette Valley and Cascade foothills. Rainfall amounts have
generally been around a couple hundredths of an inch. Slick roads
have caused numerous traffic accidents around the Portland metropolitan
area this morning. Anyway...the aforementioned area of rain appears
to be in response to a 700mb deformation zone that models suggest
will continue to shift eastward and weaken this morning.
However...enough low to middle level moisture will remain that areas of
drizzle or light rain will still be possible for much
today...especially across the west facing slopes of the Coast Range
and Cascades. With that said...surface high presure pushing
northeastward into the area...may allow skies to clear along the
central Oregon coast and Willamette Valley this afternoon.

Further additional band of rain stretches from southwest
Douglas County into far eastern Lane County. It has produced
anywhere between a tenth and a quarter of an inch across far eastern
Lane County. The NAM suggests this band will remain quasi stationary
for much of today and produce additional wetting rains across
southeastern Lane County. Based on radar trends...this band of rains
northward progression appears to have stalled...and it is beginning
to shift eastward and weaken. As a result...quantitative precipitation forecast amounts were kept
around a tenth of an inch or less for the rest of today across
eastern Lane County.

Building 500mb heights and surface high pressure nosing into the
region from the southwest should result in decreasing cloud cover and
rain chances tonight. A weak front diving southeastward still looks
on track to push into southwest Washington Friday...but any rain that
falls from it will be very light. Warm weather is still on track for
the weekend. /Neuman

Long term...Sunday through Wednesday...Sunday warm temperatures
will continue due to continued easterly flow. Sunday afternoon winds
will shift to more southwesterly with a marine surge along the coast
bringing clouds back to the coast. Southwesterly winds and marine-
sourced air will cool temperatures for Monday and Tuesday ahead of
our next weather upper-level trough approaching the West
Coast on Monday. The GFS...ECMWF...and dgex are in good agreement
that while the longwave trough stalls in the Gulf of Alaska...a
series of shortwaves sourcing from the parent low off the West Coast
will bring several chances for rain across our area Tuesday and
Wednesday. The models recently have tended to generate a lot of
moisture further in the forecast period...then back off as the event
approaches. For this reason...I am hesitant to commit to this being
a productive rainfall event. -McCoy


Aviation...a mix of MVFR and VFR ceilings today as low pressure off
the no. Calif coast streams clouds and light showers across the
region. The upper level trough axis will move across the area later
today into the evening. Once the trough axis passes...showers will
decrease and ceilings will lift. Another weak system approaching the
coast today will move inland later tonight into Friday morning. This
system will likely bring MVFR ceilings to the coast tonight and
inland Friday morning.

Kpdx and approaches...primarily VFR ceilings today and tonight. Some
occasionalmvfr ceilings with showers this morning. MVFR ceilings
expected after 11z- 12z Friday morning.


Marine...winds are expected to remain below small craft criteria
through Friday morning. Thermal low pressure is expected to
develop along the northern California coast late Friday and extend
north along the Friday night into Saturday...with potential Small
Craft Advisory northerlies spreading north through the waters.
Winds will decrease Saturday night...but a southerly wind reversal
will spread up the coast Saturday night and Sunday. Winds might
gust to 15 or even 20 knots.

Seas are expected to be around 6 feet today and 5 feet Friday with a
mixture of 16 to 18 second southwest swell and around 10 second
northwest swell. Seas then build to around 8 feet Saturday in the
strengthening northerlies...dropping back down to around 5 feet
Sunday. Tw/pt


Pqr watches/warnings/advisories...



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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 as the forecast area.

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