355 
fxus66 kpqr 200931 
afdpqr 


Area forecast discussion 
National Weather Service Portland or 
231 am PDT sun Jul 20 2008 


Synopsis...a weak upper level trough over the northeast Pacific will 
remain nearly stationary through Sunday...then slide slowly east. 
Otherwise generally zonal flow will influence the weather this week 
with seasonal temperatures and mostly dry conditions. Continued 
onshore flow will allow marine clouds to filter onshore and into the 
Willamette Valley each day. 


&& 


Short term...water vapor pictures show upper trough off the coast 
with a weak low cutting off S of 40n...as another weak shortwave 
lifts NE through Oregon. Models continue to show weak ridging over 
the forecast area in response to the upstream developing cutoff. Low 
level flow to remain onshore next few days...but thickness warming of 
air mass is expected to bring warmer temperatures today. Marine clouds seen 
on satellite still not solid along the coast as low level flow has 
become more northerly...and have been slow to develop past the Coast 
Range. 


Best guess is for upper low to move inland into northern California Monday and 
Monday night. This leaves the area of upper diffluence on the NE of the 
low S of the forecast area...limiting any potential for convection 
Monday and Monday night. Once the cutoff low moves inland...upper flow 
turns more westerly again as a weak shortwave moves in Tuesday. Marine 
layer expected to deepen considerably by Tuesday as surface flow turns 
more westerly. This will result in cooler temperatures by Tuesday...as well as a 
chance for some drizzle mainly along the north part of the coast. 


Long term...no changes. Previous discussion follows... 
medium range models bring a weak upper level trough through the 
forecast area Wednesday...with most of the energy staying north of 
the County Warning Area. Another trough will approach the forecast area near the end 
of the week. The models are keeping the troughs dry over our area and 
will continue a dry forecast through the extended period. Onshore low 
level flow will continue with late night/early morning clouds through 
the week. 
&& 


Aviation...marine layer not quite as deep as 24 hours ago. Bulk of 
stratus along the coast. Not much inland intrusion so will ease back 
on MVFR ceilings coverage inland. Most likely area to get MVFR ceilings 
will be up along the Columbia River to near kpdx for several hours 
this morning. 


Pdx and approaches...VFR prevailing. May have a few hours of a scattered 
to broken MVFR cloud deck at kpdx after 14z. 
&& 


Marine...no significant changes in forecast. Weather pattern 
diurnally driven. Expect small craft winds again this afternoon into 
the evening. No rough bar for the next 24 hours and seas remain below 
10 feet for the foreseeable future. 
&& 


Pqr watches/warnings/advisories... 
or/WA...Small Craft Advisory for winds from Cascade Head to Florence 
Sun afternoon and evening. 
&& 


Preliminary point probability of precipitation (probability of measurable precipitation) 
AST -1112 pdx 0---- sle 0---- eug 0---- 


$$ 


More weather information online at... 
http://weather.Gov/Portland 


This discussion is for northwest Oregon and southwest Washington from 
the Cascade crest to 60 nautical miles offshore. The area is commonly 
referred to as the forecast area.