Wildfire in Oregon, September 2 to 30, 2017

Area Forecast Discussion
National Weather Service Portland OR
248 PM PDT Sat Sep 2 2017

.SYNOPSIS...Strong high pressure will produce an extended period of
hot temperatures with smoke from nearby wildfires likely impacting
the region through early in the week. Temperatures should begin to
cool in the middle to latter part of the week with a chance of
thunderstorms impacting the region.

&&

.SHORT TERM...Tonight through Tuesday...Models generally showing a
surface thermal trough oscillating between the coast in the early
morning hours, to as far east as the Willamette Valley and Cascades
during the late afternoon hours each of the next few days. All the
while the strong upper level ridge axis remains over the Pacific NW.
Net result is continued hot weather, with only a modest marine
influence along the coast as any marine air remains shallow. If
there is a hottest day, Mon appears a likely candidate when the
offshore flow is depicted at its strongest. A reversal of low level
flow to the sw may come as early as Tue afternoon along the central
Oregon coast, as both GFS and EC suggest a weak surface low lifting
into the Coast Range with the thermal induced trough.

Mon night the initial batch of mid level moisture from the remnants
of tropical storm Lidia are expected to lift up into western Oregon.
Models suggest the initial shortwave lifting up with the moisture is
likely to move nw to off the central Oregon coast, which suggests
the chances for thunderstorms are likely to extend well west of the
Cascades to the coast or even coastal waters, but primarily across
the southern part of the forecast area. Tue air mass remains
potentially unstable, but without a discernable shortwave, will
limit main chance for thunderstorms to the southern part of the
Cascades.

.LONG TERM...Tuesday night through Friday...Shortwave from the
upper low that was off the south CA coast today, augmented with the
remnants of tropical storm Lidia are expected to lift north along
the Oregon coast Wed night and early Thu. Both the GFS and EC show a
sw onshore flow kicking in as early as Wed, but this will probably
will not get into a higher gear untl Wed night as the shortwave
lifts through. Some cooling, esp to the coast and into the south
Willamette Valley can be expected to begin Wed, but wholesale
cooling is likely to come Thu. Tropical moisture and a shortwave
lifting through with south to se flow in the mid levels all point to
a decent chance for thunderstorms, mainly Wed night, throughout the
forecast area. There are still modest discrepancies between the EC
and GFS in handling the incoming Pacific trough Fri with the EC
cutting the low off near the CA coast, while the GFS pushes the
trough east in the westerly flow aloft. Either solution results in
moderated temps lasting into the weekend.
&&

.AVIATION...VFR prevailing through 00Z Mon. Large area of smoke
across southwest Oregon is already over Eugene reducing
visibility with cigs around 3300 ft. This smoke will make its
way slowly northward into Salem and Newport this afternoon,
bringing cigs down to around 3500 ft and reducing vis. Farther
north is much more uncertain. As the smoke makes its way north, I
don't think the smoke will make it up to PDX, HIO, and TTD with
enough time later today to allow smoke to mix down to the surface
before sunset. I'm not confident in this, however. There is also
another threat for smoke to make it into TTD and PDX from the
east, as east winds kick in this evening. Any smoke that makes
its way through the Columbia River Gorge will be low-level smoke
and would impact visibility. Better chance for this will be at
TTD than PDX, but there is still a chance at PDX. In either case,
will likely see a cig of smoke move in to northern terminals
around 03-06Z this evening. Offshore winds developing on the
coast tonight, should keep marine clouds just offshore, so
conditions along the coast should remain VFR, except for ONP
which will see reduced vis from smoke. Sunday, expect large mass
of smoke over the area to mix down midday impacting visibility at
all terminals, except maybe AST. -McCoy

KPDX AND APPROACHES...As mentioned above, some uncertainty in
whether smoke will have time to mix down after it arrives this
evening before sunset, which will shut down the mixing. Right now
going to leave conditions VFR through Sunday morning, but will
likely see smoke mix down and impact vis starting midday Sunday.
-McCoy

&&

.MARINE...Thermal trough has moved inland, allowing winds along
the coast to start to ramp up this afternoon. Expect gusts to 20
to 25 kt over the waters this afternoon and evening, with perhaps
a few gusts to 30 kt beyond 10 nm. High pressure remains over
the waters through the next several days, but a weakening
pressure gradient will ease winds below 20 kt by Sunday morning.
Expecting winds to remain below 20 kt after Sunday morning for
the foreseeable future. Models show a weak southerly wind
reversal Tuesday morning, with winds becoming westerly to
northwesterly Tuesday afternoon. An approaching trough Wednesday
will bring another surge of southerly winds Wednesday morning.
This time the southerly winds will be a bit stronger, gusting to
15 kt.

Seas will remain near 4-6 ft through midweek next week and be
dominated by the locally driven wind. This will create choppy
conditions with steep seas through tonight. However, square-sea
conditions, such as 7 ft and 7 seconds, are not expected. -McCoy

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 10 PM PDT Tuesday for Central Oregon
     Cascade Foothills-East Slopes of the Central Oregon Coast
     Range-Mt. Hood National Forest West of Cascade Crest-North
     Oregon Cascade Foothills-North Oregon Coast Range-
     Willamette National Forest-Willamette Valley.

     Heat Advisory until 10 PM PDT Tuesday for Cascade Foothills in
     Lane County-Cascades in Lane County-Central Coast Range of
     Western Oregon-Central Columbia River Gorge-Central
     Willamette Valley-Coast Range of Northwest Oregon-Greater
     Portland Metro Area-Lower Columbia-Northern Oregon Cascade
     Foothills-Northern Oregon Cascades-South Willamette Valley-
     Upper Hood River Valley-Western Columbia River Gorge.

WA...Red Flag Warning until 10 PM PDT Tuesday for Clark County
     Lowlands-East Willapa Hills-Eastern Gifford Pinchot
     National Forest Mt Adams Ranger District-Extreme South
     Washington Cascades and Foothills.

     Heat Advisory until 10 PM PDT Tuesday for Central Columbia
     River Gorge-Greater Vancouver Area-I-5 Corridor in Cowlitz
     County-South Washington Cascade Foothills-South Washington
     Cascades-Western Columbia River Gorge-Willapa Hills.

PZ...Small Craft Advisory for winds until 5 AM PDT Sunday for Waters
     from Cape Shoalwater WA to Florence OR from 10 to 60 nm.

     Small Craft Advisory for winds until midnight PDT tonight for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 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.