FXUS66 KPQR 251610

Area Forecast Discussion
National Weather Service Portland OR
910 AM PDT Mon Jun 25 2018

.SYNOPSIS...Cooler and cloudier weather with occasional light rain
for today. A weak ridge of high pressure and seasonable weather
return Tuesday, followed by another weak trough on Wednesday.
Northwest flow then sets in for the second half of the week, with
another chance of light rain showers by Friday.


.SHORT TERM...Today through Wednesday...Cloudier and cooler weather
for today with the afternoon temperatures expected to be around 20
degrees cooler for the interior valleys than they were yesterday
afternoon, and 10 degrees cooler along the coast.

An upper trough is producing light showers mostly north of Linn and
Lane Counties this morning. Have increased POPs along the coast
range, Cascades, and foothills where the showers have been producing
light but measurable precipitation (0.01-0.15 inch). Water vapor
imagery shows a shortwave trough offshore approaching the Oregon
coast. This feature looks slightly stronger than the models are
forecasting, and expect an increase in shower activity later this
morning and early this afternoon. I therefore increased pops for this
afternoon too, mainly over the coastal mountains, foothills, and
Cascades north of Linn and Lane Counties.

The threat for rain ends late this afternoon and evening as the upper
wave moves NE of the area. Expect marine stratus to fill in along the
coast tonight, but weak ridging aloft should limit how far inland the
marine clouds will move. Light northwest winds will likely move some
clouds up the lower Columbia River along the I-5 corridor and
possibly into the Portland metro area early Tuesday morning, but do
not expect clouds to reach Salem, Eugene, or most of the foothills.

The rest of the discussion is from the previous issuance at 337
AM...Surface ridging will nose into the area Tuesday, allowing for
sunnier skies and warmer temperatures, closer to seasonal norms.
Another weak trough approaches and moves over the area Wednesday for
increasing cloudiness and a slight chance of light rain mainly along
the northern coast Wednesday. Bowen

.LONG TERM...Wednesday night through Sunday...Not many changes in the
long term. A stronger shortwave moves around the upper trough
Thursday, bringing additional chances for rain, although the 00Z
models are showing even lighter accumulations than the 12Z models
were. With pretty much all of the models showing some QPF, could go
much higher with PoPs, but with QPF trending down, wonder if it may
be a situation where accumulations amount to around a trace, thus
warranting lower PoPs. The progressive pattern continues Friday as
the trough moves to the east and upper ridging begins to nudge its
way in. Models are in agreement that NW Oregon and SW Washington will
remain on the edge of the upper high through the weekend with
seasonable temperatures. Any rain chances will depend on how strong
the high pressure is locally, but current models are showing a chance
of some light rain slipping into the area, so introduced some slight
chance PoPs to mainly the northern half of the forecast area Saturday
and Sunday mornings. Bowen


.AVIATION...A few showers in post frontal air mass today.
Extensive cloud cover over northwest Oregon and southwest
Washington with primarily VFR conditions at inland TAF sites with
occasional cigs around 2500 feet this morning. MVFR conditions at
coastal locations is expected to lift to mainly VFR this
afternoon. MVFR stratus likely returns to the coast in the
evening. The inland stratus push looks fairly limited tonight
into Tue morning, but it is possible that KPDX and KTTD will be
affected by MVFR cigs toward daybreak Tue.

PDX AND APPROACHES...Expect mostly VFR conditions today with
short periods with cigs around 2500 feet through 18Z. May see
low MVFR cigs Tue morning but confidence not high enough to
include in forecast at this time.


.MARINE...Winds were a little stronger with and behind the front
than modeled and have made upward adjustments for this morning.
But the wind trend is downward for the rest of the day.
High pressure over the northeast Pacific should result in
northerly winds for much of the week. They will become gusty Tue
and Wed, with small craft advisories likely needed for at least
the central OR waters. Another weak front may briefly turn winds
westerly to maybe even southwesterly on Thursday, before they
turn northerly again Fri into next weekend. Pyle



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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.
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