893 
fxus66 kpdt 200300 
afdpdt 


Area forecast discussion 
National Weather Service Pendleton or 
800 PM PDT Tuesday Aug 19 2008 


Short term...convective threat has come to end this evening so i've 
updated the zone package removing them from the forecast this 
evening. Main interest is the cold front pushing east of the 
Cascades. Already seeing some light rain along portions of the east 
slopes of the Cascades. This first surge of moisture will bring some 
light rain across the forecast area overnight. Models are suggesting 
a second surge of moisture coming into the area tomorrow looks like 
it could bring a more steady type rain event along with cooler 
temperatures. 


&& 


Previous discussion... /issued 130 PM PDT Tuesday Aug 19 2008/ 


Short term...tonight through Thursday night...a weather disturbance 
is currently located over south central Oregon and is moving east. 
Cumulus have been developing ahead of this system...as well as along 
the east slopes of the Cascades in the wrap-around. An isolated 
thunderstorm has formed just west of Yakima and another is forming 
just south of La Grande. Isolated thunderstorms will continue to 
develop just east of the Washington Cascades late this afternoon 
and early this evening before moving off to the east and out of the 
area later this evening. Isolated thunderstorms will also continue 
to develop across the blue and Wallowa Mountains this evening ahead 
of the disturbance. A large low pressure system is currently moving 
toward Vancouver Island and a front associated with it is 
approaching the coast. This front will move toward the Cascades late 
tonight and begin moving into the area in the early morning hours. 
This front will bring rain showers and cooler temperatures to the 
region on Wednesday. The low will then move east into southern 
British Columbia Wednesday into Thursday. This will bring breezy 
conditions Wednesday afternoon. Some instability ahead of the front 
could lead to the development of isolated thunderstorms across 
Wallowa County in the afternoon and early evening hours. 
Precipitation chances will decrease on Thursday as the system moves 
to the east and high pressure begins to build into the area. Cooler 
air behind the system and clearing skies will lead to cool overnight 
temperatures Thursday night...with areas around 5 degrees below 
normal. Dmh 


Long term...Friday through Tuesday...there will be westerly flow 
aloft on Friday as high pressure starts to build over the region. 
The high pressure continues over the area through the weekend with 
temperatures in the lower elevations warming back into the 90s for 
Sunday. Sunday night and Monday a frontal system is expected to 
move through the Pacific northwest with most of the moisture being 
caught up in the Cascades. Another trough of low pressure then 
approaches for Tuesday. There continues to be timing and strength 
differences in the models with the system on Tuesday...but should 
see temperatures cool to slightly below normal. 93 


Aviation...00z tafs...VFR conditions will prevail at all taf site 
through the next 24 hours. Some cumulus builds up and a few 
thunderstorms will be possible until 03z with the best area of 
thunderstorm development over the mountains. After 03z...a trough 
of low pressure will edge into area with showers at kdls after 03z 
and spreading east overnight. There may be some brief periods of 
MVFR with the heavier showers. 93 


&& 


Preliminary point temps/pops... 
PDT 62 77 57 76 / 30 50 40 20 
alw 66 78 60 77 / 30 50 40 20 
psc 63 81 58 80 / 30 40 30 20 
ykm 57 78 52 76 / 40 50 30 20 
hri 62 80 57 78 / 30 40 30 20 
eln 57 76 52 74 / 50 50 40 20 
rdm 54 77 48 74 / 40 50 30 20 
lgd 55 75 54 74 / 20 50 50 40 
gcd 55 79 53 77 / 20 40 40 30 
dls 62 77 60 74 / 60 50 30 20 


&& 


PDT watches/warnings/advisories... 
or...none. 
Washington...none. 
&& 


$$ 


Ti:ggg 
for additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 
91/76/76