766 
fxus66 kpdt 212333 
afdpdt 


Area forecast discussion...updated 
National Weather Service Pendleton or 
330 PM PST Friday Nov 21 2008 


Updated aviation discussion 


Short term...tonight through Sunday night...weak upper ridge over 
the area this afternoon is pushing off to the east as a cold front 
approaches the Pacific northwest. Satellite shows the front is 
moving fairly quick and should cross the region later tonight and 
early Saturday. Will see increasing clouds this evening into 
tonight. Expect a period of light rain and mountain snow overnight 
and Saturday morning. Winds will increase and locally breezy 
conditions are possible with the frontal passage. A cold westerly 
flow aloft will produce showers over the mountains on Saturday 
afternoon/evening...with clearing skies expected in the Columbia 
Basin. An upper ridge will build over the forecast area Saturday 
night and Sunday with fair weather. 94 


Long term...Monday through Friday. The shortwave ridge over the 
Pacific northwest will shift eastward early next week in response to a 
developing trough moving towards the coast. The trough is prognosticated 
to stretch and split with the southern branch strengthening into a 
closed low off the California coast. Meanwhile...the northern 
branch will send a few weak waves across Washington/or for isolated 
rain/snow showers over the mountains Tuesday and Wednesday. Another 
eastern Pacific trough will quickly follow on Thanksgiving. The 
models differ considerably with the strength and position of the low 
with the GFS stronger and farther west than the ECMWF/Canadian. 
This could mean the difference between rain and snow (snow levels 
possibly as low as 2000 feet) with winter weather concerns on 
Thanksgiving day as advertised by the GFS or a weak trough on 
Thanksgiving day with little in the way of precipitation as 
indicated by the European model (ecmwf). For now...will introduce 20-40 probability of precipitation in all 
zones as a compromise of both solutions and what is shown by the GFS 
ensemble mean. Johnson 


&& 


Aviation...00z tafs. VFR conditions will continue at all taf sites 
for the next 24 hours. There is a possibility that brief MVFR 
conditions will be met at krdm early Saturday morning with light 
snow in the vicinity of the Airport...but confidence is not high 
enough to include in the taf. Ceilings will lower to around 040-060 
this evening and will remain through 18z Saturday. The timing of 
the cold front east of the Cascades should be around 09z-15z with 
scattered light precipitation and sustained winds around 10-15kt 
during this time. Conditions will improve after 18z. Johnson 




&& 


Preliminary point temps/pops... 
PDT 38 51 31 51 / 40 30 0 0 
alw 39 51 34 49 / 40 30 0 0 
psc 35 52 30 49 / 30 10 0 0 
ykm 31 50 27 47 / 30 10 0 0 
hri 35 52 29 51 / 30 10 0 0 
eln 31 45 27 44 / 40 10 0 0 
rdm 30 48 22 51 / 30 20 0 0 
lgd 32 46 26 47 / 20 30 10 0 
gcd 33 48 27 49 / 20 30 10 0 
dls 40 51 33 49 / 40 10 0 0 


&& 


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


$$ 


Ti:ggg 
for additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 
94/85/85