Wildfire in Oregon, August 9 to 31, 2017

Area Forecast Discussion
National Weather Service Portland OR
311 PM PDT Wed Aug  9 2017

.SYNOPSIS...An upper level ridge of high pressure will keep the
region in a warm air mass through most of the work week. A weak
upper level low over northern California will remain fairly
stationary for the next few days, bringing a slight chance for
thunderstorms to the Cascades during the afternoon and evening
hours. Temperatures may cool down to near normal by the end of the
weekend as and a trough of low pressure from the Gulf of Alaska
approaches the region.

&&

.SHORT TERM...Today through Saturday...Warmest temperatures of
the week so far today with temperatures already approaching 90
degrees in many areas. Salem will easily rise above 90 degrees today
for the record 12th consecutive day above 90. In addition, dry
conditions at PDX today will increase the number of consecutive dry
days up to 54 which places this streak alone as the 3rd longest dry
streak. However, both of these streaks look like they may come to an
end as we go into the weekend.

Morning altocumulus clouds have mostly dissipated, but undoubtedly
the mid level instability is still present. In addition, the
mid-level moisture can be seen using low and mid-level water vapor
channels. Further evidence for this instability can be seen by storm
development which has begun east of the Cascades. Surface based
cumulus development along the Cascade crests should break the cap
within the next few hours with a few thunderstorms expected this
afternoon and evening. It is possible thunderstorms south and east of
the Cascades could lead to subsidence across our area. This could be
a mitigating factor for convection which will need to be watched. Any
thunderstorms which develop will certainly drop rain in the core, but
with significantly dry fuels and chances for strikes outside of the
rain core, the opportunity for additional fire starts is high.

In addition to the thunderstorms, the instability is also leading to
plume type behavior (based on satellite) from the Wapinitia fire east
of the Cascades and could lead to similar behavior from both the
Whitewater and Rebel fires in our area. Based on the amount of smoke
being emitted from this fire and additional smoke from Whitewater and
Rebel, this could lead to worsening smoky conditions in areas south
of a Mt. Jefferson to Salem line.

Increased thunderstorm chances on Thursday for the central Cascades
and have at least a slight chance of thunderstorms up the range into
the south Washington Cascades. Both instability and moisture are more
favorable tomorrow and SSEO guidance for tomorrow is somewhat bullish
in our central Oregon Cascades. This thunderstorm threat will linger
Friday and Saturday, but confidence in coverage is not as high at
this time.

Smoky conditions should improve starting on Friday as the upper ridge
finally moves east and our area returns to southwesterly flow ahead
of the trough which will impact the area into the weekend. /Bentley

.LONG TERM...Saturday night through Tuesday...Big cool down on the
way, for much more pleasant conditions for this time of year. And
for those rain-lovers, even a chance of rain!

We are seeing an upper-level trough move down onto the West Coast
Saturday night into Sunday, bringing our first chance of rain across
the entire area in a while. Expect temperatures to drop down below
normal by Sunday, for cooler weather with showers possible. Models
are still uncertain how much rain we may get across the area, but a
ball-park number of 0-0.50 inches of rain seems likely. Monday, the
back-side of the trough swings through. Not as strong as the first
shortwave, the chance of showers will likely be limited to the
coast. Temperatures should stay below normal into the beginning of
next week for a much needed break from the hot weather. Weak ridging
starts to build back in early next week, ending the chance of rain
and bringing up temperatures again midweek. -McCoy
&&

.AVIATION...Still not much change in the overall weather pattern
the next 24 hours. Weak onshore flow will continue into Thursday.
This will likely keep the coast socked in with IFR stratus the
next 24 hours. However, there could be brief periods of localized
improvement during the afternoon/evening hours. Expect primarily
VFR conditions in the interior, with occasional MVFR vsbys in the
afternoon/evening hours as the smoke aloft mixes down. MVFR marine
stratus will likely filter up the Columbia River overnight, but
still don't think it will impact the Portland metro TAF sites.

KPDX AND APPROACHES...Expect primarily VFR conditions the next 24
hours, with occasional MVFR vsbys in the afternoon/evening hours
as the smoke aloft mixes down to the surface. /64

&&

.MARINE...High pressure will continue over the northeast Pacific
through Fri. This will keep northerly winds over the waters that
will generally peak in the afternoon/evening hours, but gusts
should remain well below advisory thresholds. A weak front looks
to move across the waters late Sat into Sun and bring a brief
period of southerly winds. High pressure looks to redevelop over
the waters early next week, with thermal low pressure building
into the southern 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. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT Thursday 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.