Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 192109
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
209 PM PDT Sat Aug 19 2017

.SYNOPSIS...A weak upper disturbance passed east of the Pacific
Northwest last night and early this morning increased the onshore
flow and morning low clouds some this morning. The onshore flow tend
to continue tonight and Sunday morning, more focused along the
Columbia River and the north part of our forecast area. One last
upper disturbance will pass through Sunday afternoon and night and
maintain the onshore flow before an upper ridge builds in on Monday
and continues Tuesday for warmer temperatures. Low clouds will mainly
be along the south Washington and north Oregon coast Monday morning
and locally inland along the Columbia River. The upper ridge will
reduce the onshore flow for Tuesday. A significant upper trough will
approach Wednesday with increased onshore flow and a bit of cooling,
then some chance of showers Wednesday night and Thursday. Another
upper ridge starts to build by the weekend for drying and warming.
&&

.SHORT TERM...Tonight through Tuesday...Clouds have cleared across
southwest Washington and northwest Oregon this afternoon in the wake
of a weak upper level disturbance from overnight that increased the
onshore flow this morning. Temps are still expected to be near or
just below seasonal normals this afternoon especially inland.

Some onshore flow will continue into Sunday. The models concentrate
any morning low clouds along the south Washington and north Oregon
coasts and across the southwest Washington interior and along the
Columbia River, with a focus near the higher terrain. After that
there should be plenty of sunshine again. Temps will be around or
slightly above seasonal normals Sunday, especially inland.

One last weak upper disturbance passes through the Pacific Northwest
Sunday afternoon and evening before a modest upper ridge off the
coast builds into the Pacific Northwest Monday and Tuesday. There is
some increase in the onshore flow again Sunday night in the wake of
this disturbance. The marine clouds will be shallow with the greatest
coverage along the south Washington and north Oregon coasts. Some low
clouds will extend inland along the Columbia River through Kelso and
possibly get close to KTTD and even KPDX with brief ceilings possible
between 12z-15z. Believe these clouds in the Portland metro area will
tend to break up before the eclipse progresses much. The rest of the
day will be sunny, and with the upper ridge building in we should see
inland temps warm considerably over those of Saturday and Sunday,
possibly getting close to 90 degrees.

The modest upper ridge will continue over the Pacific Northwest on
Tuesday. The models show some morning low clouds along the coast
Tuesday morning but that coverage inland will be sparse at best.
Temps will again approach 90 inland on Tuesday.

A weak low develops over northern California early in the week and
there is a slight chance of a thunderstorm getting close to
Willamette Pass late Tuesday, though they mainly may end up being in
central Oregon. Tolleson

.LONG TERM...Tuesday night through Saturday...A decent late summer
system will approach Wednesday with increasing southwest flow aloft,
possibly increasing the onshore flow some with a bit of cooling.
There is again a slight chance of thunder near Willamette Pass late
Wednesday but the most likely scenario is that most will stay south
and east of our area. The approaching system moves through Wednesday
night and Thursday with plenty of clouds and some chance of showers.
Some lingering onshore flow will give way to more sunshine on Friday
as conditions begin to improve in the wake of the Thursday system.
Saturday is looking sunny and mild with perhaps a little fog or low
clouds at the coast. Tolleson
&&

.AVIATION...Leaned towards persistence with the forecast as there
will be little change in the weather pattern the next 24 hours. VFR
conditions this afternoon will give way to MVFR cigs along the coast
this evening. Some of the marine stratus will make it inland along
the lower Columbia River into parts of the north Willamette Valley
early Sunday morning. Can also expect to see some MVFR cigs along the
Cascade foothills early Sunday morning. The clouds should clear late
in the morning inland and by the early afternoon along the coast for
mostly clear skies and VFR conditions Sunday afternoon. North winds
will gusts again Sunday afternoon, being most noticeable along the
coast south of KTMK.

KPDX AND APPROACHES...VFR with clear skies this afternoon and
evening. MVFR CIGS expected early Sunday morning around 6 AM (13z)
with clearing around 11 AM (18z). N-NW winds will decrease tonight,
then likely increase again with gusts around 20 kt late Sunday
afternoon. ~TJ
&&

.MARINE...Made minor changes to the previous discussion last sent at
944 AM...A persistent weather pattern will result in little change in
the marine weather the next several days. High pressure holds over
the NE Pacific while a thermal trough is along the south Oregon
coast. This supports north winds across the south Washington and
north Oregon waters. The thermal trough strengthens each afternoon
such that the north winds will increase and become gusty each
afternoon. The winds south of Cascade Head will have frequent gusts
to around 25 kt beginning this afternoon which supports the current
small craft advisory for winds. This advisory has been extended in
time with the afternoon forecast package.

The seas will be locally generated from these winds and generally
remain 4 to 6 ft with periods at 9 to 10 seconds. The seas will be
choppier in the southern waters for the afternoons with dominant
periods possibly around 8 seconds. ~TJ
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 11 PM PDT Monday for
     Coastal Waters from Cascade Head OR to Florence 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. This area is
commonly referred to as the forecast area.



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