Wildfire in Oregon, August 29 to 31, 2017

Area Forecast Discussion
National Weather Service Pendleton OR
211 PM PDT Tue Aug 29 2017

.SHORT TERM...Tonight through Friday...The forecast area will remain
in a general southwest flow pattern for tonight, then an upper level
trough will approach the area on Wednesday. Currently, some moderate
CU is beginning to pop up over the Northeast Mountains, especially in
Union and Wallowa Counties. Latest SPC Mesoscale Analysis indicates
Mixed Layer CAPE values over 250 J/Kg across eastern Grant and Union
Counties, with an area of 500 J/Kg over Wallowa County. This same
area has Lifted Indices around -1 to -2 at this time, along with
mid-level lapse rates around 8-8.5 C/Km. Although there is ample
instability for t'storm development, the atmosphere is lacking
moisture and a kicker, to initiate t'storm development this evening.
In fact, there remains some subsidence behind this morning's
departing shortwave. Therefore, am inclined to hold PoPs in the
isolated category over the eastern mountains during this time. Late
tonight and Wednesday morning heights continue to fall as the
offshore trough approaches. There could be isolated showers and
perhaps an elevated t'storm moving across mainly the eastern half of
the CWA during this time. By Wednesday afternoon the main trough
axis will be along the OR/WA coast. Modest cold air advection and
breezy westerly winds (15-25 mph) will begin to push through the
Columbia Gorge and Cascade Gaps in the afternoon. There will be
lingering instability over the eastern third of the forecast area
(mainly Blue Mountains and Wallowa County) with a slight chance of
t'storms lingering there through the day. Areas of smoke/haze linger
through at least Wednesday afternoon west, and Thursday morning
central/east. Therefore an air quality alert remains in effect for
Kittitas and Klickitat Counties until 6 PM Wednesday, and the rest
of our southeast Washington counties until 10 AM Thursday. An air
quality alert is also in effect for Deschutes County until Noon on
Friday. The trough axis passes by to the east on Thursday with a dry
northwest flow developing behind it for our area. Temperatures will
see a slight cooldown, but will remain above average. Highs on
Thursday will be in the mid-80s to lower 90s...except 70s and lower
80s in the mountains. Both Thursday and Friday morning will feature
rather cool low temperatures...dipping into the 50s...except upper
30s and 40s in the mountains/high valleys. By Friday, a large,
anomalous upper level ridge moves into the Pacific Northwest. This
will mean dry weather, clear skies and a return to well above
average temperatures. Highs reach well into the 90s for the
valleys/basins with 80s in the mountains. 77

.LONG TERM...Friday night through Tuesday.  Very hot and dry
conditions are expected through the extended period as an area of
high pressure builds over the interior northwest.  High temperatures
on Saturday and Sunday are expected to be at or near record highs
with readings in the upper 90s to low 100s for the lower elevations
and 90s for the mountains. On Monday, the ridge should be drifting
east with slightly cooler readings for Monday and Tuesday.  As the
ridge shifts east, this would allow some moisture to be transported
north from California into southern Oregon.  The GFS model is more
aggressive with the moisture and instability than the EC or Canadian
and this will need to be monitored as the ridge moves east. 93

&&

.AVIATION...00Z Tafs.  Mainly VFR conditions will continue through
the next 24 hours.  Areas of smoke/haze along the East Slopes of the
Cascades, are affecting KDLS, KRDM and KBND at times with VIS from 2-
5SM.  Otherwise mostly clear skies will prevail with light winds. 93

&&

.FIRE WEATHER...Breezy/locally windy conditions can be expected
Wednesday afternoon/early evening, but with minimum RHs occurring
before the highest winds arriving, will continue to highlight the
threat in the Fire Weather Planning Forecast, and not issue a Red
Flag Warning.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  64  94  58  88 /  10  10  10   0
ALW  69  94  63  89 /  10  10   0   0
PSC  62  96  58  92 /  10  10   0   0
YKM  62  96  58  91 /   0   0   0   0
HRI  63  96  60  92 /  10  10   0   0
ELN  63  90  59  88 /   0   0   0   0
RDM  52  90  44  88 /   0  10   0   0
LGD  52  93  48  86 /  20  20  10   0
GCD  60  94  49  88 /  10  10   0   0
DLS  65  89  63  91 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

77/93/93/80