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Area forecast discussion 
National Weather Service Pendleton or 
745 PM PDT Friday Mar 19 2010 


Update...only a few high clouds are over the forecast area this 
evening...otherwise it is a quiet evening under a strong high 
pressure ridge aloft. The upper ridge axis will cross the Cascade 
crest overnight and move over eastern Oregon and Washington on 
Saturday. 850 mb temperatures increase from about 4-6 c today to 
about 10-12 degrees c on Saturday. Saturday will be the warmest day 
this weekend with highs easily getting to the middle 60s to perhaps 
lower 70s in the lower elevations and mainly 50s in the mountains. A 
weather system will begin to push clouds into the region on 
Sunday...but the most recent model runs have slowed this system 
down...so the first part of Sunday should remain dry with just 
increasing clouds. Precipitation is introduced in the mountains 
first on Sunday afternoon...mainly over the Cascade east slopes. By 
late Sunday afternoon clouds and showers will spread to cover the 
eastern mountains with a chance of showers...and at least a slight 
chance for the lower elevations as moisture increases in a southwest 
flow aloft ahead of the upper trough with this next system. The 
trough will move across the region on Monday bringing the best 
chance of precipitation...with snow in the higher mountains on Monday. 
Conditions will begin to improve again Monday night and Tuesday as a 
another upper ridge builds over the Pacific northwest. 88 


&& 


Aviation...06z tafs...VFR conditions with light winds under 15 kts 
will persist through the next 24 hours. 88 


&& 


Previous discussion... /issued 235 PM PDT Friday Mar 19 2010/ 


Short term...tonight through Monday...a ridge of high pressure will 
remain over the area through tomorrow. The ridge axis will move from 
offshore this afternoon to near the Washington-Oregon-Idaho border 
by Saturday afternoon. This will give the area clear skies and fair 
weather until then. Tonight should be another cool evening as clear 
skies and light winds allow for radiative cooling but with a warmer 
air mass...temperatures will be several degrees warmer overall from 
last night. Tomorrow will also see a good warmup over today as the 
ridge axis moves overhead. Temperatures will be in the 60s in most 
locations with middle 50s to lower 60s in the mountains. In the 
afternoon a trough will approach the coast and skies will begin 
clouding up. Pressure gradients will tighten up and afternoon and 
evening winds will pick up to 10 to 20 miles per hour with 15 to 25 miles per hour in the 
Grande Ronde Valley. A few rain showers will move into the Cascades 
after midnight Saturday night and rain showers will gradually cross 
the area except for Wallowa County during the day on Sunday. Behind 
the front...a trough will follow and this will keep rain showers 
continuing over the entire region through Sunday night. Colder air 
will come in with the trough and snow levels will drop from around 
7000 feet to 5000 feet Sunday night. Precipitation amounts are not 
that substantial so snow amounts will be on the order of 1 to 3 
inches. Monday will see mainly mountain rain showers as the lower 
elevations dry out. Temperatures will drop several degrees Sunday 
and again on Monday putting US back in the 50s and lower 60s. Perry 


Long term...Monday night through Friday...the 12z runs of the GFS 
and the European model (ecmwf) are in fairly good agreement through the long term 
period. Rain showers and snow showers will continue Monday night as 
the low moves into the Great Basin and sends wrap-around moisture 
into the area. Precipitation is expected to taper off on 
Tuesday...but a few showers could be possible over the eastern 
mountains due to upslope flow. A ridge of high pressure will then 
strengthen over the area on Tuesday night for drier conditions that 
should last through Wednesday afternoon. Another fast moving trough 
will push through the region Wednesday night and Thursday...bringing 
a chance of rain and mountain snow. There may be a brief break in 
the activity on Thursday night...but a second stronger trough is 
forecast to move inland on Friday. 82 


Aviation...00z tafs...only a few high thin clouds will move across 
the area today and tonight. Otherwise...expect VFR condition with 
light winds under 15 kts. 82 


&& 


Preliminary point temps/pops... 
PDT 30 64 39 60 / 0 0 0 30 
alw 34 64 42 62 / 0 0 0 30 
psc 29 64 39 61 / 0 0 0 20 
ykm 30 63 37 60 / 0 0 10 30 
hri 28 65 38 62 / 0 0 0 20 
eln 29 62 38 59 / 0 0 10 40 
rdm 24 68 34 58 / 0 0 10 20 
lgd 29 58 37 60 / 0 0 0 20 
gcd 29 62 36 61 / 0 0 0 20 
dls 31 64 41 58 / 0 0 20 40 


&& 


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


&& 


Threat index 
Saturday : green 
Sunday : green 
Monday : 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 


$$ 


88/82/88