Area forecast discussion...updated aviation discussion 
National Weather Service Pendleton or 
1020 PM PDT Friday Aug 28 2015 


Update...satellite picture show large area of clouds across the 
forecast area, but precipitation is having a hard time making it 
onshore. This should change over the few hours as water vapor 
pictures show piece of energy near 140w dropping south and as it 
continues to move it will kick low near 130w northeastward and 
some light rain will spread into the Cascades by morning. Will 
update forecast for slightly slower onset of precipitation. 93 


&& 


Previous discussion... /issued 250 PM PDT Friday Aug 28 2015/ 


Short term...tonight through Sunday night...a large upper level 
trough of low pressure continues to extend from the Gulf of Alaska 
south to the eastern Pacific. The trough axis roughly runs along 135 
west longitude, but will shift to near 130 west Saturday. Southwest 
flow aloft associated with the trough will keep varying chances of 
showers going along the Cascade east slopes tonight. Patchy smoke 
will continue across the region as well, with thicker areas of smoke 
in southeast Grant County. As the trough shifts east Saturday, it 
will kick an upper low currently near 38n/135w northeast through the 
region. The main impact from this system across southeast 
Washington, and northeast and central Oregon will be winds. At this 
time winds over a good portion of the area will run in the 25 to 35 
miles per hour range. Thus will continue most of the current wind advisories. 
Have cancelled the advisories for the Kittitas Valley and the 
Columbia River gorge as winds in these areas should stay in the 20 
to 30 miles per hour range. Brief stronger winds could locally occur during 
cold frontal passage though. This low will cause chances of showers 
from south-central Washington south to central Oregon. Also a few 
showers may occur over northeast Oregon in the afternoon. There is 
an outside chance of a stray thunderstorm over Wallowa County 
Saturday afternoon and evening. The upper trough will move into and 
through the Pacific northwest Sunday and Sunday night. Thus still 
expect to see some chances of showers over much of the region 
Sunday, with showers lingering along the Cascade east slopes of 
Washington into Sunday night. Breezy winds will again be possible 
over the Columbia Basin, but will be mainly in the 15 to 25 miles per hour 
range. High temperatures by Sunday afternoon will run in the upper 60s to 
middle 70s, with middle 50s to middle 60s in the mountains. 90 


Long term...Monday through Friday...a large upper level trough will 
be over the region on Monday and then it will develop into a deep 
trough focused over the Pacific northwest by midweek. Temperatures 
will be slightly below normal Monday and Tuesday then drop even 
further with highs only in the 70s by midweek. There will be a 
chance of showers mainly along the Cascades Monday and Tuesday then 
a more widespread chance of precipitation Wednesday and Thursday as 
the trough deepens over the northwest. Cool and drier conditions are 
expected by Friday. 


Aviation...06z tafs...VFR conditions will continue for the next 24 
hours but are expecting a frontal passage early to midday Saturday. 
Ceilings will be broken to overcast at 8k-12k feet above ground level but again 
could see some lower ceilings around frontal passage time. Smoke 
from regional wildfires will continue to be present across the area 
but are not expected to lower visibilities to MVFR at any taf site. 
Showers will develop along the front and approach the Cascades after 
10z but the probability of rain showers at any taf site is fairly 
low due to rain shadowing. A significant wind increase is expected 
with the frontal passage on Saturday of 20-30 kts and higher gust 
resulting in blowing dust and reduced surface visibilities. 91/93 


Fire weather...upper low and frontal boundary currently offshore 
will move across the region Saturday. This will produce strong west 
to southwest winds. Some rain is expected along the Cascades and 
east slopes otherwise mainly dry. Another system will move through 
Saturday night and Sunday. This will bring a better chance of 
showers along with cooler temperatures. An upper level trough will 
remain over the west through next week with cooler temperatures. 


&& 


Preliminary point temps/pops... 
PDT 60 82 54 72 / 10 10 10 30 
alw 66 83 60 74 / 10 20 10 40 
psc 60 83 52 77 / 10 10 20 30 
ykm 60 73 50 70 / 10 20 40 20 
hri 61 84 53 76 / 0 10 10 30 
eln 58 73 51 71 / 20 30 50 30 
rdm 57 77 44 68 / 10 30 20 20 
lgd 53 84 47 69 / 10 20 10 30 
gcd 56 81 46 73 / 10 20 10 20 
dls 64 79 60 73 / 20 30 40 30 


&& 


PDT watches/warnings/advisories... 
or...Wind Advisory from 5 am to 6 PM PDT Saturday for orz510-511. 


Red flag warning from 7 am to 7 PM PDT Saturday for orz640>645. 


Blowing dust advisory from 9 am to 6 PM PDT Saturday for orz044- 
507-508. 


Wind Advisory from 9 am to 6 PM PDT Saturday for orz044-507-508. 


Washington...red flag warning from 7 am to 7 PM PDT Saturday for waz641-643- 
645-675. 


Blowing dust advisory from 9 am to 6 PM PDT Saturday for 
waz027>029. 


Wind Advisory from 9 am to 6 PM PDT Saturday for waz027>029-521. 


&& 


For additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 


$$ 


93/91/91 



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