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Area forecast discussion 
National Weather Service Portland or
856 am PDT Tuesday Sep 2 2014

Synopsis...an incoming front will bring increasing clouds and a
chance for light rain showers to mainly southwest Washington and
extreme northwest Oregon late this afternoon and evening. Morning
clouds should once again return Wednesday...and result in one last
day with temperatures near to slightly below normal. Strengthening
offshore winds will allow temperatures to rise into the upper 80s
and low 90s for many inland locations late in the work week. There
is a chance another storm system could bring a chance for light rain
showers to the area early next week.

&&

Short term...today through Friday...satellite imagery shows a layer
of marine low clouds stretching from the foothills from Troutdale
eastward southwestward to Eugene. There is also some low clouds along
the north coast and near the central coast.

An upper level trough approaching the Washington coast this morning will
move southeastward across Washington later today. A trailing front
will slide southeastward across the northern half of the area late
this afternoon and evening...resulting in a few light showers across
southwest Washington...and the west facing slopes of the north
Oregon Cascades and Coast Range. Rainfall will be quite light with
this system. However...this system will keep temperatures down a tad
today and Wednesday...with temperatures topping out near normal to a couple
degrees below normal. As the front moves through the area...it will
push the surface high pressure southward into a position that should
allow marine clouds to develop across much of northwest Oregon
tonight into Wednesday morning.

Strengthening high pressure over the northeast Pacific and weak upper
level troughing over southwest Oregon and northern California...will
turn middle level winds more northeasterly over the area. This will
allow thermal low pressure currently over northern California to
build up the coast late Wednesday into Thursday. This should result
in temperatures rising into the upper 80s and low 90s for
the Willamette Valley Friday and Saturday. In addition...poor
night time relative humidity recoveries and modest east winds across
the Cascades and Coast Range will enhance fire weather concerns the latter
part of the week. Tw/neuman



Long term...Saturday through Monday...no changes...previous
discussion follows....a weak...positively-tilted trough will move
through our area late this week. Not only is moisture limited for
the passage of this system...but any precipitation that does develop
should be east of the Cascade Ridge...outside of our area. Late this
weekend the GFS...ECMWF...and dgex all are suggesting a longwave
trough will move onshore bringing a chance for some rainfall Sunday
night or Monday. Disagreement between models on timing and because of
how far out this system is in the forecast period...there is a lot of
uncertainty with this system. Kept probability of precipitation the same as they capture this
uncertainty well. -McCoy

&&

Aviation...variety of flight conditions across the region this
morning behind a weak cold front that moved across the area early
this morning. Much of the interior remains VFR with a scattered-broken deck
around 4000 feet...though some remnants of a low MVFR stratus layer
remain along the Columbia River...and south Willamette Valley.
These may linger a bit this morning and while some areas may
clear...a scattered-broken layer around 4000 feet may persist through the
afternoon. Clouds increase this evening as the next front
moves in...with MVFR ceilings likely and a chance for -ra across the
northern areas. At the coast...conditions have generally improved
with local areas of fog/low stratus. As flow becomes more onshore
may see some ceilings develop along the coastal areas...and will
again return to low MVFR/IFR this evening.

Kpdx and approaches...VFR conditions today...with increasing
clouds late this afternoon with the next weak cold front. MVFR
ceilings develop this evening with slight chance of rain shower later
this evening. Cullen

&&

Marine...a weakening cold front will move across the waters this
evening... and may be strong enough to produce some S-SW gusts to
20 knots along the S Washington coast as it moves onshore. Behind the
front...winds again shift north-northwest with gusts to 20 knots...but cannot
rule out a occasional stronger gusts primarily over the northern
outer waters.

North-northwest winds will increase for second half of week as high pressure
strengthens offshore and thermal low pressure extends north from
California. Gusts 20-25 knots appear likely along the central Oregon
waters by Wednesday afternoon...then expanding north across the waters on
Thursday. Winds should ease for Friday and Sat as the offshore high pressure
weakens. Cullen

&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...none.
&&

$$

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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.

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