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fxus66 kpdt 210324 
afdpdt 


Area forecast discussion 
National Weather Service Pendleton or 
830 PM PDT Sat Mar 20 2010 


Update...winds have slowly decreased across the Grande Ronde Valley 
this evening as clouds increase across the region. Radars showing 
line of showers moving into southwest Washington at this time. A 
cold front moves into eastern Washington and Oregon by Sunday 
morning. Current forecast has rain increasing from west to east 
across the area during the day on Sunday and timing looks good. 
Will update winds in Grande Ronde Valley..otherwise no changes. Ml 


&& 


Previous discussion... /issued 230 PM PDT Sat Mar 20 2010/ 


Short term...tonight through Tuesday..an upper level low and front 
are approaching the Pacific northwest coast this afternoon. The low 
is expected to move northeastward into British Columbia by tomorrow. 
Ahead of the front...a moist southwest flow will move into the area 
late tonight and overrunning precipitation will begin in the 
Cascades late tonight and expand across the area tomorrow. Models 
are bringing it in about 6 hours faster than yesterday so have moved 
the progression of the system up to match this. Satellite imagery 
shows the leading edge of the precipitation just about at the coast 
so the faster timing looks right. Have also beefed up probability of precipitation quite a 
bit for tomorrow afternoon and night as confidence is high that 
this system will produce up to two tenths of an inch of liquid 
precipitation in the low lands and up to half an inch in the 
mountains Sunday through Monday. Initially snow levels will be 
around 5000 feet but by late Sunday night and Monday morning snow 
levels will be down to around 3500 feet. Thus anticipate the blue 
and Wallowa Mountains getting 2 to 6 inches of snow Sunday night and 
Monday while the Cascades will see 2 to 5 inches above 3500 feet but 
perhaps an inch or two on the Lower Mountain passes. Cooler air will 
move in with the front and temperatures will drop into the 50s 
tomorrow and Monday perhaps a degree or two warmer. With heavy cloud 
cover from this system...nighttime temperatures will be in the upper 
20s to upper 30s tonight and Sunday night. By Monday night... the 
system will be clearing the area and an upper level ridge will begin 
building over the area. A few showers will linger in the eastern 
mountains Monday night before the area dries out on Tuesday. 
Temperatures Tuesday will rebound into the upper 50s to lower 60s. 
The southern Grande Ronde Valley will continue to be windy with 
winds of 25 to 35 miles per hour with gusts to 40 miles per hour this evening before 
calming down overnight. Area winds will be breezy for the most part 
tomorrow through Monday evening. Perry 


Long term...Tuesday night through Saturday...an upper level ridge 
will be over the area through Wednesday followed by a potentially 
strong trough on Wednesday night and Thursday. The trough will bring 
a good chance of rain and High Mountain snow. As this system lifts 
NE of the region and deamplifies Thursday night...another lower 
amplitude system will bring continued unsettled weather through the 
end of the week. Neither of these systems are expected to tap 
significant cold air...so snow will be confined to the higher 
mountain elevations. Overall...temperatures are expected to be above 
normal through the forecast period. 78 


Aviation...00z tafs...current set of tafs is largely on track and a 
slow increase and lowering of the cloud cover is expected overnight 
tonight. Areas of rain/rain showers will develop during the morning 
hours tomorrow and increase during the afternoon. However...VFR 
conditions are expected to prevail with winds under 15 knots through 
00z Monday. By Sunday afternoon a general ceiling of 5-8 kft above ground level can 
be expected. 78 


&& 


Preliminary point temps/pops... 
PDT 39 57 38 55 / 0 50 50 20 
alw 42 58 41 57 / 0 50 50 30 
psc 38 59 39 61 / 0 40 30 10 
ykm 37 58 35 60 / 10 30 30 10 
hri 38 59 37 61 / 0 40 40 20 
eln 37 57 35 57 / 10 40 40 20 
rdm 33 55 28 51 / 0 40 40 20 
lgd 37 55 37 50 / 0 50 50 40 
gcd 35 56 35 49 / 0 50 50 30 
dls 41 56 39 57 / 10 50 30 20 


&& 


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


Threat index 
Sunday : 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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