Wildfire in Oregon, August 10 to 31, 2017

Area Forecast Discussion
National Weather Service Portland OR
253 PM PDT Thu Aug 10 2017

.SYNOPSIS...A warm pattern remains in place through Friday as upper
level high pressure persists over the region. Meanwhile, an upper
level low to the south will support chances for thunderstorms across
the Oregon Cascades through Friday night, especially south of Mt.
Jefferson. However, a change in the pattern develops across the area
this weekend with much cooler conditions and a chance of rain on
Sunday as a weak front crosses the Pacific Northwest.

&&

.SHORT TERM...Tonight through Sunday...Low stratus remains along the
coastal areas of Washington and Oregon this afternoon but has cleared
along the lower reaches of the Columbia River west of Skamokawa.
Meanwhile, latest satellite imagery reveals cumulus build-ups across
the eastern portions of Lane and Linn Counties, with a few
thunderstorms already developing. A few thunderstorms have also
developed east of the Cascades, so the environment will continue to
be supportive of thunderstorms through the afternoon and evening.
With the storm motion in southeast to west-northwest direction, will
need to continue to monitor storm evolution this evening, as it is
possible some storms may move west from the Cascades into the
foothills or even the Willamette Valley, particularly south of Marion
County. The best chance for a storm to sneak far enough west looks to
be in the Corvallis to Cottage Grove corridor.

The persistent upper level ridge will linger through part of the day
Friday before finally shifting to the east by the weekend as the
upstream upper trough approaches. Onshore surface pressure gradient
increases overnight, which will enable more widespread marine stratus
into the gaps and along the lower Columbia, with more widespread
morning stratus filling into the interior Friday as compared to this
morning. As the upper low over southwestern Oregon/northern
California continues to lift north and east and weaken on Friday,
another round of thunderstorms are possible - primarily near the
Cascades and foothills. As the upper trough drops south from the Gulf
of Alaska and across the northeastern Pacific, expect increasing
onshore flow that will help to increase mixing and help to improve
the recent smoke and haze issues across the region. This improvement
may initially be slow late Friday, but become more noticeable
Saturday.

 Much cooler conditions over the weekend across the region, with
afternoon highs only in the lower to mid 80s inland on Saturday as
the upper trough approaches the region. An associated surface front
will enhance precipitation chances late Saturday into Sunday with the
most widespread chance for rain in some time. However, though PoPs
continued to be trended higher, the amount of rain expected remains
rather small. In addition to more widespread cloud cover, the most
significant change will be temperatures that top out in the mid to
upper 70s. If the current forecast for Portland holds, Sunday could
be the coolest day in nearly a month.	Cullen

.LONG TERM...Sunday night through Wednesday...The start of next week
will remain on the cool side - particularly when compared to recent
temperatures. The upper level trough migrates eastward on Monday,
with more zonal flow developing over the region. Moisture will be
limited, so the rain chances will depart rather quickly. Heights will
gradually rise through the week as the air mass warms, so
temperatures can be expected to linger near seasonal normals Tuesday
before slightly above normal by midweek. Another upper level
disturbance may approach the Pacific NW by the second half of next
week.	Cullen

&&

.AVIATION...Weak onshore flow under high pressure aloft will
continue to produce IFR cigs along the coast. However, there
could be brief periods of local MVFR this afternoon/evening.
Smoky conditions will continue to produce a mix of MVFR and VFR
vsbys in the interior through around 06Z this evening. Marine
stratus will redevelop along the Columbia River late tonight and
is expected to impact KPDX and KTTD between 13-17Z Fri. Stratus
filtering into the southern valley overnight will also bring a
period of reduced cigs to KEUG and KSLE between 11-18Z Fri.

KPDX AND APPROACHES...Predominately VFR, with occasional MVFR
vsbys through around 06Z this evening. Marine stratus filtering
up the Columbia River will likely bring a brief period of high-
end IFR /low-end MVFR cigs between 14-16Z Fri. /64

&&

.MARINE...High pres will continue over the NE Pac through Fri.
This will keep N winds over the waters that will generally peak
in the afternoon/evening hours, but gusts should remain below
advisory criteria. A weak front looks to move across the waters
late Sat into Sun and bring a brief period of S winds. High pres
redevelops over the waters early next week, with thermal low pres
building into the S Oregon coast. This could bring a brief period
of advisory gusts to 25 kt Mon afternoon/evening.

Seas will remain below 5 ft through the weekend. Seas may briefly
build to around 6 to 7 ft early next week as the northerly winds
increase. Otherwise, expect seas to remain below 7 ft through the
period. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT this evening for Willamette
     National Forest.

WA...None.

PZ...None.

&&

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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.