979 
fxus66 kpdt 150442 aaa 
afdpdt 


Area forecast discussion 
National Weather Service Pendleton or 
940 PM PDT sun Mar 14 2010 


Updated aviation discussion 


Update...a ridge of high pressure will gradually shift eastward 
tonight and tomorrow as a low pressure system in the eastern Pacific 
moves toward the Pacific northwest. A front is currently just off 
shore and is expected to continue to slow as a disturbance rotates 
around the bottom of the trough. Ahead of this front...a disturbance 
is pushing showers across western Washington. East of the 
Cascades...dry conditions are expected to continue through the 
night. High level clouds will continue to spread ahead of this front 
and over the region. This will help keep temperatures warmer 
tomorrow morning than this morning. Current forecast looks to be on 
track and do not anticipate any updates this evening. Dmh 


&& 


Aviation...06z tafs...middle and high level clouds will continue 
across the region for the next 24 hours with VFR conditions 
expected. Winds will remain below 10 kts for most taf sites through 
tomorrow. Dmh 
&& 


Previous discussion... /issued 350 PM PDT sun Mar 14 2010/ 


Short term...tonight through Wednesday afternoon...a middle/upper 
level ridge of high pressure will continue over the forecast area 
tonight and Monday for dry conditions. Winds aloft will back to the 
south on Monday night in response to a strong middle/upper level low 
deepening between 130-140w while the middle/upper level ridge is over 
Idaho/Montana. This puts the forecast area well east of increasing 
moisture approaching the coast overnight ahead of a cold front 
pushed toward the Pacific northwest by the low. As such areas east 
of the Cascades will remain dry Monday night...except for a low 
chance of rain along the central Washington Cascade crests 
overnight. The low sweeps the cold front inland during the day on 
Tuesday with the front moving into the western sections of the 
forecast area Tuesday afternoon. The front will usher in a chance of 
rain along the east slopes of the central and southern Washington 
Cascades and the Oregon Cascades Tuesday with rain likely near the 
crests in the afternoon. The front then moves across the rest of the 
forecast area Tuesday evening. As such probability of precipitation on Tuesday evening will 
be in the likely category but quantitative precipitation forecast amounts are going to be on the 
light side at lower terrain elevations. The northeast mountains of 
Oregon are likely to receive 0.10-0.20 inches of rain from the 
frontal passage. Snow levels will decrease Tuesday night to around 
2500 feet after midnight so rain will transition to snow at pass 
levels by middle evening. Then a weak...low amplitude middle/upper level 
trough moves inland on Wednesday. This system will mainly bring middle 
and high level clouds over the forecast area on Wednesday with dry 
conditions predominating...except for a chance of snow showers along 
the east slopes of the central Washington Cascades. Polan 


Long term...Wednesday night through Sunday. Confidence in the 
medium-range models is fairly strong through the end of the week but 
fades late in the period. High pressure will strengthen offshore 
early in the extended period leaving Washington/or under a northerly flow 
aloft. A shortwave moving south along The Rockies may bring a few 
showers in extreme NE Oregon but may also bring increasing winds to 
portions of the area--nothing significant but locally breezy. The 
ridge will shift eastward with the axis of the ridge along the 
Cascades by Friday. This will result in a dry and warming trend 
Thursday and Friday. At this time...will keep temperatures slightly above 
seasonal average but future shifts may go warmer if models increase 
heights even more. Will also keep Friday night and Saturday dry with 
little weather change...although models are hinting at a weak wave 
overriding the ridge. The 12z European model (ecmwf) has backed off on the strength 
of the shortwave compared to its previous run. Upstream off the 
eastern Pacific...the European model (ecmwf) is much stronger than the GFS with an 
upper low that eventually approaches the coast over the weekend. 
The GFS ensemble is a compromise of both solutions. Keeping this in 
mind...forecasting climatology on probability of precipitation and temperatures on Sunday 
seems to be the best option. Johnson 


&& 


Preliminary point temps/pops... 
PDT 53 35 62 40 / 0 0 0 0 
alw 56 38 62 43 / 0 0 0 0 
psc 56 32 64 37 / 0 0 0 0 
ykm 53 32 61 37 / 0 0 0 0 
hri 57 32 64 35 / 0 0 0 0 
eln 55 30 59 36 / 0 0 0 0 
rdm 56 27 62 38 / 0 0 0 0 
lgd 47 31 59 38 / 0 0 0 0 
gcd 49 26 58 33 / 0 0 0 0 
dls 54 36 62 38 / 0 0 0 10 


&& 


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


Threat index 
today : green 
Monday : green 
Tuesday : green 


Green: none or limited need for watches, warnings, or advisories. 
Yellow: a few watches, warnings, or advisories possible or in effect. 
Red: numerous watches, warnings, or advisories possible or in effect. 


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


$$ 


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