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Area forecast discussion 
National Weather Service Portland or
224 PM PDT Wednesday Jul 23 2014

Synopsis...an unseasonably strong and cool low pressure system was
centered off the Washington coast this afternoon...with a cold front
moving through southwest Washington and northwest Oregon. The
low center will swing through tonight and early Thursday for
continued showers. There is a chance of thunderstorms through this
evening. A few showers will linger through Thursday...otherwise
higher pressure will then build with dry and warmer weather by Friday
and continuing through the weekend into next week.
&&

Short term...tonight through Saturday...an unseasonably cool and
strong low pressure system was still centered off the Washington
coast this afternoon. The cold front that moved onshore early this
morning was still over the area early this afternoon...and satellite
extrapolation shows that the back edge of the solid clouds should
clear the Willamette Valley around 22z or 23z and east of the
Cascades shortly after that. Once the back edge moves through... we
will see some brief heating during which we will see our high temperature
for the day...and if there are any thunderstorms...TI will be during
that period...the late afternoon and early evening.

The low center itself comes onshore tonight and moves through western
Washington. The models show part of the bent back occlusion on the
back or west side of the low will swing through our northern forecast
zones from about the Columbia River or Portland northward or so
overnight tonight and early Thursday. There may be some steady rain
with this feature...and another shot of decent quantitative precipitation forecast amounts. There
have been some lightning strikes detected with this feature off the
Washington coast today...so will keep some thunderstorms along the
north coast tonight as this feature moves onshore.

The low moves out to the east pretty early Thursday morning...but
there is still quite a bit of westerly flow through much of the day
Thursday with clouds in the north from about Salem northward being
slow to clear. A few showers will also linger through the afternoon
especially in the north. Temperatures will start to rebound some Thursday
and get into the lower to middle 70s...warmest south.

An upper ridge...though initially quite flat...will slowly start to
move in Friday for a return to more seasonable dry weather with some
morning clouds and afternoon sunshine. Temperatures will finally approach 80
again inland. The warming will continue in earnest on Saturday as 500
mb heights build into at least the middle 580s...with plenty of sunshine
pretty much across the entire forecast area after some brief morning
clouds mainly in the north. Look for inland highs well up in the 80s
Saturday...possibly getting close to 90 in some areas. Tolleson

Long term...high pressure will continue to build over the Pacific
northwest ahead of a shortwave trough...forecast to come onshore
sometime late Sunday night or Monday morning. There is still
uncertainty on the time this system will move into our area and the
location of any associated precipitation. The wave is unresolved in
the mean 500-mb height field from gefs and naefs...but the GFS and
European model (ecmwf) both have it moving through Sunday night or early Monday
morning. Behind this system...the large upper-level ridge is
forecast to continue to build in amplitude and westward and will
become centered over The Rockies by mid-week. Southwesterly upper-
level flow and clear skies inland will keep temperatures fairly warm
over our area Tuesday and Wednesday. -McCoy
&&

Aviation...the main frontal line continues to push onshore this
afternoon with lower ceilings and locally heavy rain. Behind the
line...the coastal areas have become VFR with a scattered layer
around 3000 feet and another above 5000 feet. Gusty winds to 25 knots
possible along the central Oregon coast near konp through this
evening. As of 21z ceilings across the Willamette Valley have followed
suit with a few local MVFR pockets remaining under heavier rain.
Given this clearing occurring...threat for few thunderstorms remains
across the area but not enough confidence concerning timing or
location to include in tafs. Then as low pressure system moves onshore
later tonight...expect another round of MVFR/IFR ceilings and visibilities
around 06z at the coast. Expect ceilings around 2500-3500 feet after 10z
across the interior.

Kpdx and approaches...expect VFR to continue for another hour or two
with ceilings around 3000-3500 feet. Few lingering showers possible this
evening along with about a 20 percent chance of thunderstorms early
tonight. Another round of rain and lowering ceilings likely arrives
around 12z as low pressure system moves through. Cullen
&&

Marine...winds have increased today as a low pressure system moves near
the waters towards the Washington/Oregon coast. Small Craft Advisory
continues through early Thursday morning as gusts to 30 kts possible.
Cannot rule out a thunderstorm this evening or early tonight over the
waters which may be accompanied by gusty winds or small hail. Seas
will remain 5 to 7 feet through tonight and will be somewhat steep at
times as dominant periods are around 7 seconds. Do not anticipate
waters reaching hazardous seas criteria at this time...but will
monitor this afternoon.

Winds will ease somewhat later Thursday...before high pressure redevelops over
NE Pacific and a thermal low pressure builds over north California. This will
bring a return to gusty north winds and steep wind driven
seas...particularly in the late afternoon and evening hours...for Friday
through the weekend. Cullen
&&

Pqr watches/warnings/advisories...
or...WA...none.
Pz...Small Craft Advisory for winds until 6 am PDT Thursday for
coastal waters from Cape Shoalwater Washington to Cascade Head or out
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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