Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 271713 AAA
AFDPDT

Area Forecast Discussion...Update
National Weather Service Pendleton OR
1012 AM PDT SAT AUG 27 2016

Updated Aviation Discussion

.SHORT TERM...Today through tonight...An upper level low will sweep
across western Canada today and exit into central Canada overnight.
The impact of this on the forecast area will be a weak cool front
passage which will increase winds this afternoon and into the
evening before decreasing overnight. Could see some patchy blowing
dust this afternoon around the lower Columbia Basin with some
locally reduced visibilities.

&&

.FIRE WEATHER...A cold front currently along the Olympic Peninsula
will sweep across eastern Washington this afternoon.  Winds will
increase ahead and behind the front and will be SW-W 15-25G35 mph
across the Columbia Basin and surrounding valleys.  The relative
humidity during this time will be 15-25 pct.  Red Flag Warnings are
in effect from 1 PM to 9 PM today for the Lower Columbia Basin,
areas in and around the Eastern Columbia River Gorge, the Yakima
Valley, and the Blue Mtn Foothills.  The upper level flow will shift
to the west this weekend then southwest early next week.  A
shortwave embedded in the southwest flow will track across eastern
Oregon on Tuesday...bringing isolated showers and thunderstorms.
The weather pattern will change from a persistent high pressure
ridge to a persistent upper level trough next week. Therefore...fire
weather concerns will shift from the wind/RH threat to a threat of
thunderstorms beginning Tuesday.  It will become increasingly wet by
the end of the week...but I do not expect a significant rain event.
Wister

&&

.AVIATION...18Z TAFS...VFR conditions will prevail through the
forecast period. SCT to BKN mid and high level clouds(12K to 25K FT
AGL)are expected across the Washington terminals through the
afternoon and evening hours. Most of the Oregon terminals will only
see sct high level clouds near 25K FT AGL.

West winds will be the primary concern this afternoon and evening.
Winds are increasing to 15-30 KT with some higher gusts before
diminishing after 28/03-04z. With the stronger winds there could
certainly be some BLDU/HZ INVOF KPDT mainly from 22z to 01z. Not
enough confidence to add into the TAF forecast for KPSC...but could
also be around here at times as well. 77

&&

.PREV DISCUSSION... /issued 257 AM PDT SAT AUG 27 2016/

SHORT TERM...Today through Monday Night...A broad trough covers
much of Canada and the US this morning with a ridge out in the
Eastern Pacific. Satellite imagery clearly shows an upper low in the
Canadian Rockies moving through the trough. This low will push a dry
cold front through the area later today. While there will be some
increase in cloudiness in the Washington portion of the area, no
precipitation is expected. The main impact will be breezy to windy
conditions late this morning through this evening in the Columbia
Gorge, Columbia Basin and adjacent valleys. West to northwest winds
of 15 to 30 mph are expected there this afternoon and early evening
with 10 to 20 mph winds elsewhere. Winds will decrease in the
evening. Temperatures today will be similar to yesterday and with
humidity remaining low, fire weather concerns will be high. A Red
Flag Warning remains out for the the Columbia Gorge, Columbia Basin
and surrounding valleys this afternoon through this evening. A more
detailed discussion of the the fire danger can be found in the fire
weather discussion below. Tonight the upper low will move east into
Central Alberta while the front will remain hung up along the Blue
Mountains and will gradually dissipate through Sunday morning.
Partly cloudy skies will continue over the Washington portion of the
area while the Oregon portion will be mostly clear. This will help
keep low temperatures tonight in the upper 50s to mid 60s in the
north while the mountains and the south will be in mid 40s to mid
50s. Sunday and Sunday night another upper low will move south along
the British Columbia coast and deepen the trough offshore. The upper
flow will turn more southwesterly but temperatures will cool a few
degrees as cooler air moves into the area. Skies will become mostly
clear and winds will remain light with no precipitation expected. On
Monday and Monday night, circulation around the trough will help
build a ridge over the Rockies. While we will be on the western
fringe of the ridge, rising heights will help warm us back to the
mid 80s to lower 90s in the lower elevations and into the 80s in the
mountains. Perry

LONG TERM...Tuesday through Saturday...A shortwave trough will move
NEWD across eastern Oregon Tuesday afternoon and evening. There may
be just enough instability and forcing for a few thunderstorms until
mid evening. For Wednesday and Thursday the models have trended much
drier compared to previous runs with just weak troughing over the
area. There will likely be some cloud cover and cooler temperatures
with highs of 80-85 in the lower elevations. As a large-scale trough
consolidates over the western U.S. on Friday there will be a better
chance for showers areawide. Instability parameters look weak on
Friday except for over Wallowa County so the thunderstorm threat
appears rather limited. The thunderstorm potential will increase on
Saturday...especially in the afternoon and evening with the trough
overhead. Some locations could see decent amounts of rainfall
depending on where the showers tend to concentrate. It will be cool
Friday and Saturday with highs mainly in the 70s lower elevations
and 60s in the mountains.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  90  61  85  58 /   0   0   0   0
ALW  91  66  86  64 /   0   0   0   0
PSC  93  60  88  59 /   0   0   0   0
YKM  90  56  88  56 /   0   0   0   0
HRI  91  61  87  58 /   0   0   0   0
ELN  84  56  86  55 /   0   0   0   0
RDM  89  49  89  49 /   0   0   0   0
LGD  89  54  87  52 /   0   0   0   0
GCD  89  54  87  55 /   0   0   0   0
DLS  88  64  88  61 /   0   0   0   0

&&

.PDT Watches/Warnings/Advisories...
OR...Red Flag Warning from 1 PM this afternoon to 9 PM PDT this
     evening for ORZ639-641.

WA...Red Flag Warning from 1 PM this afternoon to 9 PM PDT this
     evening for WAZ639-641-675.

&&

$$

91/77/77



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