Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 221800 AAA

Area Forecast Discussion
National Weather Service Pendleton OR
1100 AM PDT Fri Sep 22 2017

.SHORT TERM...Satellite this morning shows upper low centered over
Idaho with clouds rotating around the low into eastern and central
Oregon. Expect skies will remain partly to mostly cloudy today.
Isolated showers over the mountains especially John Day highlands
to the Wallowa mtns. Airmass aloft remains cool and highs will be
in the 50s and 60s. 12z models continue to show upper ridge
building into the region this weekend with fair weather. 94


.AVIATION...18Z TAFs...A long wave upper trough over the region will
keep partly to mostly cloudy skies over the area through the next 24
hours. There may be isolated to scattered light showers over the
mountains through this evening which will not affect any of the TAF
sites. Winds will be light and generally 12 kts or less through the
next 24 hours. Perry


.PREV DISCUSSION... /issued 248 AM PDT Fri Sep 22 2017/

SHORT TERM...Today through Sunday night...An upper level low
pressure system will continue to spin over SE OR and Western ID
through the day. This will keep skies partly to mostly cloudy with
scattered showers along the East Slopes of the Cascades and
especially over the eastern mountains. In fact, there will be
numerous showers(rain and snow) in the afternoon over the Eagle Cap
mountains...closer to the upper level low. The Lower Columbia Basin
and surrounding valleys are expected to remain dry today. Snow
levels will hover around 5000-6000 feet through the day. Model
guidance is not indicating much if any instability for this
afternoon...and the area only had 1 CG lightning strike yesterday will leave any mention of thunder out of the forecast. High
temperatures will remain below average this afternoon...only
reaching 60-65 in the valleys/basins...with upper 40s and 50s in the
mountains. By tonight, the upper level low shifts further east and
begins to weaken. This will allow any lingering mountain showers to
quickly taper off...with partly cloudy skies prevailing overnight.
Temperatures could drop quickly, depending on how much clearing the
area sees. For now, am expecting overnight lows in the upper 30s and
40s for the Columbia Basin and surrounding lowlands...with mid-20s
to mid-30s in the mountains and high valleys. Will issue an SPS to
cover the potential for sub-freezing temperatures in Central Oregon
and the Grande Ronde Valley. A freeze warning may eventually be
needed for one or both of these zones...if skies end up mostly clear
and winds stay light tonight(good radiational cooling conditions).
The forecast area looks to stay dry, under partly cloudy skies and a
northerly flow regime for the upcoming weekend. Winds will remain
light and temperatures will see a gradual warming trend. High
temperatures will be very close to the seasonal the
upper 60s and lower 70s for the valleys/basins...with upper 50s to
mid-60s mountains. The area will begin to see an increase in mid to
high level cloud cover later Sunday night as a weak weather system
rides over the top of the high amplitude offshore ridge. 77

LONG TERM...Monday through Friday...A lingering upper trough will
keep some limited moisture over the far eastern mountains and the
central Washington Cascade east slopes on Monday. There may be
enough moisture for a slight chance of showers in these areas on
Monday. Elsewhere it will be dry. Beginning Tuesday a high amplitude
high pressure ridge along the coast will take control of the weather
over the region with dry, stable conditions and a warming trend. The
long range models are in fairly good agreement with this scenario.
Temperatures will start out in the upper 60s to mid 70s lower
elevations...warming to the mid 70s to lower 80s by Friday. It will
be about 10 degrees cooler in the mountains. Subsidence under the
ridge will keep the atmosphere stable so there will not be any
threat of showers or thunderstorms through the period Tuesday
through Friday either. Winds will be mostly light and generally
about 15 kts or less. 88


PDT  63  42  67  43 /  10  10  10   0
ALW  66  46  70  46 /  10  10  10   0
PSC  68  43  73  43 /  10  10  10   0
YKM  67  45  71  45 /  10  10  10   0
HRI  67  42  71  43 /  10  10  10   0
ELN  67  45  70  43 /  10  10  10   0
RDM  59  30  66  34 /  10  10  10   0
LGD  56  34  62  36 /  20  10  10  10
GCD  56  33  65  39 /  20  10  10  10
DLS  69  47  74  48 /  10  10  10   0




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