FXUS66 KPQR 192141

Area Forecast Discussion
National Weather Service Portland OR
241 PM PDT Sun Aug 19 2018

.SYNOPSIS...A weak upper level low pressure system will move
across the Pacific NW early this week. The system is relatively dry
though, and the only chances for precpitation is a slight chance for
thunderstorms in the Cascades Mon. Otherwise low level flow becomes
more northerly Mon and Tue for warming temps and an influx of smoke
and haze into the region from fires burning in BC and eastern WA.
Cooler weather is expected to return toward the end of the week as
westerly flow at the surface and aloft return a marine air mass to
the region.


.SHORT TERM...Tonight through Wednesday...An upper low was off the
central Oregon coast near 125W early this afternoon. Satellite and
models continue to indicate a predomianantly dry system as it moves
onshore tonight, which should preclude any real chance for
convection. Once the upper low moves inland, low level flow turns
more northerly as a trough of low pressure develops up the coast
Mon. This is likely to limit the diurnal push of marine clouds to
the Coast Range valleys late tonight and Mon morning, while drawing
low level smoke and haze down through western WA and into nw Oregon
by late tonight and Mon. As the initial upper low continues east
Mon, models bring another short wave moving down from the north, and
dig the trough sw again. Despite it's continental origins, there are
indications in the models of some mid level moistue being pulled in
to help provide a little instability. So for now, will keep a slight
chance for thunderstorms in over the Cascades Mon afternoon and
evening as the shortwave moves sw across the forecast area.

Offshore flow strnegthens Mon night and Tue with the thermal induced
trough strengthening along the coast. This will make for a
relatively warm night Mon night, and Tue is likely to be the warmest
day of the week as offshore winds pair with inland 850 mb temps
around 20C to 21C. The offshore flow will tend to reinforce the
presence of haze and smoke over the region, which is likely to take
a few degrees off the potential high temperatures. As the upper
trough axis sinks south into sw OR Tue, any small chance for
thunderstorms is likely to become relegated to the Lane county
Cascades as air mass stabilizes under subsidence aloft further

Tue night and Wed models seem pretty intent on beginning to move the
upper trough east, developing a west or sw onshore push in its wake.
As the push develops during the day and 850 mb temps in the models
are slow to come down Wed, there is probably a limited amount of
cooling in store for the inland areas, especially in the north. The
onshore flow though should allow for some improvements to air
quality as marine air begins to push in.

.LONG TERM...Wednesday night through Sunday...Ridge starts breaking
down late on Wednesday with a shortwave trough approaching, and a
pretty strong marine push Wednesday night into Thursday morning.
With flow generally northwesterly, stratus will likely push into the
north Willamette Valley, but will probably not make it down to Salem
or Eugene. Temperatures on Thursday will be much cooler, with highs
generally in the upper 70s to low 80s inland.

A northwesterly upper-level flow pattern sets up for later this
week, meaning onshore flow and westerly winds aloft. Good news
about this is that it should keep smoke out of our area going into
next weekend. Seasonable temperatures should continue as well, with
highs inland in the upper 70s to low 80s, and morning clouds on the
coast breaking up in the afternoons. Next piece of good news is the
potential for a deep upper-level trough that the models are showing
could bring some rain either late next weekend or early the
following week. For those who want rain, don't get your hopes up to
high just yet. This is still a long ways out, and as the models have
shown in recent weeks, much can change this far out in the forecast.


.AVIATION...Marine stratus will continue to bring a mix of IFR to
low end MVFR cigs through 00z Tuesday. Some smoke has already
filtered into the region and may result in MVFR visibilities at
our northern taf sites today, but the worst of the smoke is yet
to come. Increasing northeasterly flow later tonight and Monday
should result in plenty of smoke spreading over the region.
Expect widespread MVFR visibilities with pockets of IFR visibilities
to develop between 06-18z Monday.

KPDX AND APPROACHES...Additional smoke to our north and east
will spread across the area tonight and Monday. This smoke will
likely mix down to the surface and create MVFR and possibly even
IFR visibilities. If it does not occur later on tonight then it
will almost certainly impact visibilities towards 18z Monday when
daytime heating allows smoke aloft to mix down to the surface.


.MARINE...High pressure over the northeast Pacific and thermally
induced low pressure over northern California and the Great Basin
will more or less continue for much of the week. This will result
in little day to day change in winds and seas. As a result, wind
gusts should generally remain below 20 kt through the week with
seas hovering in the 4 to 6 ft range. Seas will be a little
choppy towards the middle of the week as multiple wave trains
with dominant periods between 7 and 11 seconds move across the
waters. There are some hints that a front could turn winds out of
the south with gusts approaching Small Craft Advisory levels of
25 kt at least briefly next weekend. /Neuman





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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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