Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 191715 AAA

Area Forecast Discussion
National Weather Service Pendleton OR
1016 AM PDT Sat Aug 19 2017

.SHORT TERM...Today and tonight...A flat zonal flow will continue
with some minor disturbances passing to the north. This will leave
skies mostly clear and near normal temperatures. Will see some
locally breezy winds in the afternoon and evening along the east
slopes of the Cascades otherwise pretty normal wind pattern. No
major changes made in the morning update.

.AVIATION...18Z TAFS...VFR conditions are forecast to continue
through the next 24 hours at all terminals. Upper level cloudiness
will increase across the area this afternoon/evening as moisture
riding over the ridge offshore moves into the area. North-
northwesterly transport winds will keep the smoke plume from the
Milli fire northwest of Bend west of the BDN/RDM terminals with only
limited impacts to visibility expected from any lingering smoke in
the area. Winds will be generally light and diurnal, except at DLS
where they will gust into the mid-upper 20s this afternoon and
evening. 74


.PREV DISCUSSION... /issued 358 AM PDT Sat Aug 19 2017/

SHORT TERM...Today through Monday night...A broad upper trough will
keep a general westerly flow over the forecast area today. This
flow will continue to push cooler marine air into eastern Oregon and
Washington through the Cascade gaps and the Columbia River Gorge.
Temperatures today, as a result, will be cooler than Friday with
lower elevation readings in the lower to mid 80s...and mostly 70s in
the mountains. Winds will be lighter and humidities will be a bit
higher and therefore fire weather conditions are not expected to
become critical. The flow aloft will gradually become northwest as
the broad upper trough moves to the east and an upper ridge builds
off the coast. This will keep dry and stable conditions over the CWA
through Monday night. Skies will be mostly clear through the period
with perhaps just some high thin cirrus at times. This should be
good viewing weather for the total eclipse on Monday. Winds will be
light through the period...except perhaps a little breezy through
the Cascade gaps at times during the afternoons and early evening. 88

LONG TERM...Tuesday through Saturday...The extended period starts
off with dry weather and mostly clear skies on Tuesday. Temperatures
remain above average, with afternoon highs reaching 92-98 in the
valleys/basins and mid-80s to lower 90s mountains. By Tuesday night
moisture and elevated instability begin to increase as the flow
turns more southwesterly. This will bring a slight chance for a
shower or t`storm from about Bend to John day and points south. A
large, highly amplified trough begins to approach the area from the
Northeast Pacific through the day on Wednesday. Latest model
guidance is in very good agreement in the details/timing of
this system. Both the 00z GFS and ECMWF indicate a closed low at
500mb (~551dm) just off the north-central BC coast by 5PM Wednesday
will slide southeast over southern BC by 5PM Thursday. As this
system approaches, increasing moisture and instability will provide
a chance of showers and t`storms over the eastern half of the CWA
from Wednesday afternoon into the overnight hours. These t`storms
could certainly pose a fire weather threat, as fuels remain
extremely dry. Temperature remain quite warm out ahead of the front
on Wednesday, again reaching the 90s in the lower elevations, with
80s mountains. Then, on Thursday, as the surface cold front moves
across the area...expect still a slight chance of t`storms lingering
over eastern Grant, Union and Wallowa Counties. There will be a
slight chance of rain showers along the immediate Cascade Crest in
Washington as well. Otherwise, temperatures will be much cooler (10-
15 degrees) for all locations on Thursday. All signs are now
pointing to breezy or even windy conditions developing Thursday
afternoon behind the previously mentioned cold front. There will be
strong cold air advection, tightening pressure gradients, fairly
strong winds aloft and a punch of mid-level dry air. All of these
factors will allow gusty winds to effectively mix down to the
surface. At this time, westerly winds of 15-25 mph with higher gusts
are looking likely. Decided to add in a mention of blowing dust
Thursday afternoon in the Lower Columbia Basin/Foothills, as the
current guidance would indicate a good setup for this potential.
Afternoon RH values will remain fairly low (18-28 percent)on
Thursday, which will not only aid in the blowing dust potential, but
also bring about fire weather concerns(for strong winds/low RH). As
this system swings by our area should be under a more zonal, drying
flow for Friday. As winds decrease and skies clear expect a chilly
start Friday and Saturday morning...with lows dropping into the
40s/low 50s...except 30s in the mountains and high valleys. High
temperatures Friday will be about 5 degrees below average...80-85 in
the lower elevations with 70s in the mountains. By next Saturday,
heights begin to rise as an upper level ridge builds over the
forecast area. This should mean dry weather, mostly clear skies and
warming temperatures. 77


PDT  83  58  82  54 /   0   0   0   0
ALW  84  61  84  57 /   0   0   0   0
PSC  87  56  86  57 /   0   0   0   0
YKM  86  58  86  56 /   0   0   0   0
HRI  86  59  85  56 /   0   0   0   0
ELN  82  59  82  54 /   0   0   0   0
RDM  83  46  83  46 /   0   0   0   0
LGD  81  51  80  48 /   0   0   0   0
GCD  83  52  83  48 /   0   0   0   0
DLS  84  63  83  62 /   0   0   0   0




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