266 
fxus66 kpdt 220403 
afdpdt 


Area forecast discussion 
National Weather Service Pendleton or 
800 PM PST Friday Nov 21 2008 


Update...an area of light rain has moved into western Oregon and 
Washington during the past couple of hours. The rain has reached as 
far east as Portland...with rain and snow over the Cascades to 
Stampede Pass in Washington and not quite to the Oregon Cascade 
crest yet. The cold front and precipitation with a weather 
disturbance will move into eastern Oregon and Washington overnight 
and eventually across the forecast area. Due to the weak nature of 
this weather system and fast movement precipitation amounts will be 
light. A few inches of snow are possible over the mountains 
generally above 4000 feet. Locally breezy conditions will develop 
behind the cold front early Saturday morning. High pressure aloft 
will then return to the region Saturday night into Sunday with a 
return to fair weather. 88 


&& 


Aviation...(06z tafs) generally VFR conditions will continue at all 
taf sites for the next 24 hours. However...there may be brief 
periods of MVFR or IFR overnight in lowered ceilings and/or 
visibility as rain showers and higher elevation snow Showers Pass 
with a cold front. 88 


&& 


Previous discussion... /issued 330 PM PST Friday Nov 21 2008/ 


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 


&& 


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 
88/85/88