Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 232125

Area Forecast Discussion
National Weather Service Pendleton OR
225 PM PDT Wed Aug 23 2017

.SHORT TERM...Tonight through Sunday...Moisture continues to stream
over the forecast area but waiting for the heat of the day to begin
triggering convection. Already seeing this occurring over southern
and southeast Oregon so it`s just a matter of time. As such, will
see isolated to scattered thunderstorms mainly over the eastern
portion of the forecast area this evening and into tonight before a
gradual shift to the east takes place and thunderstorm activity
wanes. Still, with an approaching frontal system there could be
enough forcing for nocturnal thunderstorms over far eastern portion
of forecast area after midnight. The approaching front will sweep
across eastern Washington and northern Oregon early Thursday but the
front stalls and stretches from central Idaho back to south central
Oregon by afternoon. This means there will still be some lingering
instability from eastern Crook county up through Wallowa county for
some possible afternoon and evening convection Thursday. Behind the
front an upper level trough will be moving into western Canada and
northern Washington producing some locally breezy conditions and
ushering in some cooler air. By Friday the trough is exiting leaving
the region under a cool but dry westerly flow. Saturday the flow
will begin to lift northward as a ridge of high pressure begins to
build over the region and temperatures begin to warm up.

.LONG TERM...Saturday night through Wednesday...A large upper ridge
will build over the region through the extended period. The ridge
will be mostly centered over the Great Basin but very warm
temperatures will push NWD into the Pacific NW beginning Sunday into
next week. Monday and Tuesday look to be the hottest
days...potentially in the low 100s for highs across the Columbia
Basin and adjacent lowlands...but each day Sunday through Thursday
will be hot. There is some concern that monsoon moisture circulating
around the ridge could work its way up into eastern Oregon and
extreme southeast Washington Tuesday and Wednesday as depicted by
the GFS model. This could lead to isolated thunderstorm development.
However...the ECMWF model is dry during the period and there does
not appear to be a forcing mechanism for storms other than daytime
heating over the higher terrain. Therefore...have opted to keep the
forecast dry for now. Winds do not appear to be significant through
Thursday. 78


.AVIATION...00Z TAFS...Mostly VFR conditions are expected through
the forecast period. Thunderstorms have yet to develop across the
area this afternoon due to extensive cloud cover. However expect
TSTMS to form around 22Z in central Oregon where skies have cleared.
Once they do form they will spread newd toward the KPDT and KALW
areas this evening. sub VFR conditions may occur vcnty of SHRA and
TSRA. Also lingering smoke VCNTY KRDM and KBDN will cause some MVFR
VSBYS. Elsewhere expect mid and high clouds through the evening
hours followed by clearing late tonight. Some thunderstorm activity
is expected again on Thursday...mainly from the eastern mountains
eastward so the TAF sites should see minimal impacts. Winds will
pick up Thursday afternoon to westerly 12 to 25 kt except 20-30 kt
at KDLS. 78


.FIRE WEATHER...Thunderstorm coverage will increase with the
approach of a cold front this evening. Cloud cover has inhibited
convective development this afternoon. However some areas of
clearing started by 1 PM. There still is significant instability
over Central to Northeast Oregon so development may occur...
especially in areas of clearing where heating will be strongest.
Cumulus has developed in Grant and Wallowa Counties in Oregon. The
approaching front will keep elevated instability over Central to
Northeast Oregon all night so isolated to scattered thunderstorms
are possible. I will leave current Red Flag Warnings in place and
monitor development. Even though the latest short term models
indicate that thunderstorms may linger longer in the Central Oregon
Mountains than originally anticipated this evening I will not extend
the Red Flag Warning for an area where nothing has started yet.

Models continue to slow the progression of the front on Thursday,
Isolated thunderstorms will linger across far eastern Oregon
tomorrow. Winds will increase in behind the front, with breezy to
locally windy conditions for the Columbia Gorge and Basin. Model
trends have been a bit lighter for winds, and with the maximum winds
likely occurring when RHs are beginning to rise, I do not expect any
RFWs for Thursday. 76


PDT  62  82  50  81 /  30   0   0   0
ALW  66  84  54  82 /  40  10   0   0
PSC  65  86  51  83 /  20   0   0   0
YKM  60  84  48  82 /  10   0   0   0
HRI  65  86  51  83 /  20   0   0   0
ELN  62  77  51  81 /  10   0   0   0
RDM  52  80  42  82 /  20   0   0   0
LGD  58  80  48  80 /  50  10  10   0
GCD  57  81  50  83 /  60  20  10   0
DLS  65  81  56  85 /   0   0   0   0


OR...Red Flag Warning until 10 PM PDT this evening for ORZ642-644-645.

     Red Flag Warning from 5 PM this afternoon to 10 PM PDT this
     evening for ORZ643.

     Red Flag Warning until 5 PM PDT this afternoon for ORZ611-640.

WA...Red Flag Warning from 5 PM this afternoon to 10 PM PDT this
     evening for WAZ643-645.



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