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Area forecast discussion 
National Weather Service Portland or
908 am PDT sun Oct 4 2015

Synopsis...high pressure is building into the Pacific northwest
today. Gusty east winds are beginning to develop over the higher
terrain...and should develop through the Columbia Gorge
today and Monday as thermal low pressure builds north along the
Oregon coast. The dry offshore flow will bring plenty of sunshine and
warm daytime temperatures all the way to the coast...while nights
will be seasonably cool where winds go calm. A southerly wind
reversal is likely to spread up the coast by Tuesday bringing
temperatures back down closer to early October normals. A series of
disturbances is expected to erode the high pressure ridge later in
the week...gradually increasing the chance for rain across the
forecast area by next weekend.


Update...not much to update this morning with big bubble no trouble
in command. Upper level high pressure will continue to build into the
region today with thermal low pressure building up the coast.
Offshore flow increases later today but will not be as strong as the
event we saw last week. Winds will be noticeably breezy in spots but
with no real impacts. Some high clouds are beginning to push in
around Pacific County and Astoria this morning and it looks like they
will continue across the forecast area bumped sky cover up
to partly cloudy for the immediately affected area. Otherwise the
forecast appears to be well on track with a warm and dry day in
store. Bowen

Short term (previous discussion) through Tuesday...the
overall forecast picture looks pretty well on track this
morning...with the region set to experience a couple days of sunny
and warm weather all the way to the coast. Water vapor imagery shows
the upper level low which brought some light rain to the district
Friday night and early Saturday pushing southward through California.
Meanwhile high pressure both at the surface and aloft are building
into the Pacific northwest. The resulting NE flow aloft is drying out
the air mass...and today should see abundant sunshine throughout the

The 10z observation from keug continues to show a north wind around
10 miles per hour...which makes sense given the 1-2 mb northerly kpdx-keug
gradients that have been in place overnight. This wind is likely
enough to keep all but the most wind-sheltered valleys mixed enough
to prevent all but a few patches of shallow ground we
decided to remove fog from the forecast this morning. With wall to
wall sunshine and offshore flow we should come close to realizing the
full potential of the +12 to +14 degree c 850 mb temperatures...resulting in
temperatures near 80 degrees for the Willamette Valley and only slightly
cooler along the coast. Little change is expected Monday...perhaps
slightly warmer as 500 mb heights and 850 mb temperatures increase a bit.

Temperatures will fall quickly overnight tonight where decoupling occurs.
Models have backed off a bit on the magnitude of easterly gradients
through The Gorge tonight...with the 06z NAM only showing kttd-kdls
gradients peaking around -3 mb. With such gradients it may be a
challenge to keep the sheltered valleys well mixed throughout the temperatures will probably fall well into the 40s and possibly
even upper 30s in the outlying valleys. Meanwhile gusty east winds
will keep temperatures up overnight in the West Columbia gorge tonight and
Monday night...but east winds are not expected to be quite as strong
as they were with last weeks east wind event. Expect some gusts 20-25
miles per hour near Troutdale...25-35 miles per hour near Corbett...and 35-45 miles per hour at the
strongest wind spots like Crown Point.

The models are pointing at a southerly wind reversal and a southerly
stratus surge along the coast Monday night and Tuesday in response to
increasing southwest flow aloft and thermal low pressure developing
over eastern Washington. This should bring substantial cooling to the
coast...and the leakage of marine air should ease temperatures inland
Tuesday back down into the lower to middle 70s. Weagle


Long term (previous discussion)...Tuesday night through
Saturday...the extended forecast period will likely see a
continuation of above normal temperatures as upper level ridging
builds over the western United States. 00z models show some
disagreement in how to handle small shortwaves riding over the top of
the upper ridge...with the 00z Gem and to a lesser extent the 00z
European model (ecmwf) showing some quantitative precipitation forecast spreading across the district Wednesday.
Meanwhile the 00z/06z GFS remain drier...with only the north coast
getting clipped by a warm front Wednesday. Much will depend on the ejection
of the upper low presently over California... as it will
have some influence on how amplified our upper ridge becomes. Past
experience would favor the drier GFS solution Wednesday... but we decided
to keep some low probability of precipitation in the forecast in case the wetter solutions
pan out.

Models do show good agreement in the overall amplifying trend of the
upper ridge over the western Continental U.S. Thu/Fri. Bumped up forecast temperatures a
few degrees in turn...bringing them closer in line with latest
guidance. The amplifying ridge should also push the jet into a more
meridional Mode...increasing the chance of some sort of atmospheric
river scenario developing over NE Pacific Fri-sun. Whether or not this
deeper moisture will impact the Pacific northwest is still in question though
the 00z GFS...ECMWF...and Gem all agree that a Pacific frontal system
will approach the coast Sat/sun. With timing in is
difficult to pinpoint a day for focused probability of decided to go with
a gradual trend of increasing probability of precipitation toward/above climatology throughout the
forecast area Sat/sun. Given the baroclinicity involved between the
upper ridge and the approaching deep upper trough...there is some
potential for coastal wind next weekend as this frontal system and
possible waves of low pressure along the front approach. Weagle


Aviation...predominantly VFR conditions prevail next 24 hours under
dry offshore flow. Local IFR radiational fog will linger through
about 17z sun before clearing completely. Easterly winds
crossing the Cascade and Coast Range are expected to gust in the
20 to 30 knots range today then ease this evening.

Kpdx and approaches...VFR the next 24 hours with increasing winds
out of the east to northeast today. /27


Marine...high pressure over the northeast Pacific and thermal low
pressure over the Oregon coast will bring periods of gusty north
to northeast today. Overall expect winds to remain below small
advisory criteria today. However models show marginal Small Craft
Advisory winds developing over the central coast zones 10 to 60 nm
out for this afternoon into early evening.

Seas continue to slowly subside...ranging from 5 to 7 feet early this
morning. Wave models are performing better today and are in line
with observations. Boaters should be aware that seas will be
steep across the central Oregon waters today especially over the
waters west of 10 nm offshore.

High pressure over the northeast Pacific will weaken early next
week allowing winds to ease on Monday. Models continue to show a
southerly surge moving up the Oregon coast late Monday into early
Tuesday...with the GFS showing the potential for a coastal jet
developing for a few hours Tuesday afternoon. Southerly winds will
continue through the end of the week as the next system approaches
the waters. /Mh


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory for winds until 9 PM PDT this evening for
waters from Cascade Head to Florence or from 10 to 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.

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