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FXUS66 KPDT 212126
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
226 PM PDT Mon Aug 21 2017

.SHORT TERM...Tonight through Thursday...An upper level ridge will
be transitioning over the forecast area overnight and then shift
east of the forecast area on Tuesday. This will allow the
development of a southwesterly flow to develop in response to an
upper level trough approaching western Canada. Moisture associated
with a small low pressure system off the coast of Southern
California will begin to be picked up by this southwest flow on
Tuesday and spread across central to northeast Oregon Tuesday night
and Wednesday. There will be a slight threat of some convective
showers and or thunderstorms Tuesday night but a bigger threat on
Wednesday as the upper level trough begins to interact with this
moisture. A frontal passage associated with the upper level trough
will occur Wednesday night and early Thursday. This will push any
remaining convective moisture east of the forecast area by
afternoon. Other impacts will be increasing westerly winds which
could produce some patchy blowing dust and temperatures will be
around 10 degrees compared to Wednesday.

.LONG TERM...Thursday night through Saturday night...The mid/upper
trough that pushed the cold front through the region Wednesday night
and Thursday morning moves across the forecast area Thursday night
and exits the forecast area into Idaho by daybreak Friday. Breezy
surface winds (2-minute average wind speeds of 15-25 mph) and patchy
blowing dust are expected Thursday evening in the Kittitas Valley,
the Eastern Columbia River Gorge, the Lower Columbia Basin, Blue
Mountain Foothills and north central Oregon. Winds will diminish
overnight as pressure gradients weaken.

A dry westerly flow in mid/upper levels sets up east of the Cascades
during the day on Friday and this flat upper level pressure pattern
continues through Friday night resulting in downslope westerly winds
aloft, which yield subsidence and dry conditions from sunup Friday
to sunup Saturday. High temperatures on Friday will be around 2-5
degrees warmer than Thursday's highs, generally in the lower to mid
80s, and in the mid 60s to upper 70s in the mountains. The
aforementioned ridge amplifies and strengthens over the interior
Pacific Northwest Saturday and Saturday night thus allowing the
warming trend and dry conditions to persist through the weekend with
lowland high temperatures Saturday in the mid 80s to lower 90s and
in the lower 70s to mid 80s in the highlands. Polan

Sunday afternoon through Tuesday morning...Models are in a good
agreement that broad upper level ridging will remain in place over
the area Sunday through Monday night with light winds and generally
clear skies. High temperatures in the lower elevations on Sunday and
Monday will be in the 90s running near 10 degrees ahead of normals
for most locations. The 12Z runs of the GFS and ECMWF slowly weaken
and shift the ridge to the east with southwesterly flow returning to
the area by Monday night. Have increased PoPs slightly over the
southeastern third of our CWA to reflect some potential for
development of isolated showers. 74

&&

.AVIATION...00z TAFs...VFR conditions and clear skies will persist
over the next 24 hours at all terminals. Smoke and haze from the
wildfire immediately west of Sisters will continue to impact the
BDN/RDM area intermittently with surface visibilities varying
between 5-10SM. Winds will remain light, diurnal and terrain driven
less than 10 KTs through the period. Winds will increase to 5-15 KTs
from the NW to N at KRDM, KBDN, KDLS and KPDT from late Tuesday
morning through Tuesday afternoon. Polan


&&


.FIRE WEATHER...Quiet weather expected through Tuesday morning.
Isolated thunderstorms will be possible across mainly central Oregon
Tuesday afternoon as a trough of low pressure begins to approach.
Thunderstorm coverage will increase Wednesday afternoon/night with
the approach/passage of a cold front, with scattered thunderstorms
expected across Central Oregon in the afternoon, migrating eastward
across the northeast Oregon mountains Wednesday night. Will issue a
Fire Weather Watch for zones 611, 640, 642, 643, 644 and 645 for the
potential of abundant lightning and gusty thunderstorm winds. Winds
will increase in the wake of the front Thursday, 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, will not issue any
watches for Thursday at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT 56 96 61 92 / 0 0 0 10
ALW 60 97 64 92 / 0 0 0 10
PSC 56 97 64 94 / 0 0 0 0
YKM 59 97 62 93 / 0 0 0 0
HRI 56 98 62 93 / 0 0 0 10
ELN 55 96 59 90 / 0 0 0 0
RDM 49 94 51 88 / 0 10 20 20
LGD 51 95 54 90 / 0 10 10 20
GCD 54 97 56 89 / 0 10 20 30
DLS 62 97 66 89 / 0 0 0 0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Wednesday afternoon through late
Wednesday night for ORZ642>645.

Fire Weather Watch from Wednesday afternoon through Wednesday
evening for ORZ611-640.

WA...Fire Weather Watch from Wednesday afternoon through late
Wednesday night for WAZ643-645.

&&

$$

91/99/99
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