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Area forecast discussion 
National Weather Service Portland or 
900 am PDT Friday Jul 18 2008 


Synopsis...a weak upper level trough over the northeast Pacific will 
slowly move east over the next few days. This will result in seasonal 
temperatures and dry weather...but with marine clouds affecting the 
coastal areas. 


&& 


Short term...visible satellite imagery shows marine stratus layer 
to be similar in coverage to yesterday...with the stratus solid along 
the coast and over the Coast Range. The inland extent of the stratus 
is up the Columbia River to Portland and vicinity area...and along 
the west slopes of the Coast Range...with a few more scattered clouds 
in the central Willamette Valley. The layer is much deeper than 
yesterday with tops around 4000 feet...surface observations have 
recorded drizzle in kast earlier this morning. High temperatures 
expected to be a few degrees lower than yesterday as 500 mb heights and 
850 mb temperatures are lower. 


Water vapor loops show an upper level low moving slowly east through 
southern b.C. With a trough extending over WA/Oregon...and another 
trough extending out to near 43n/138w. Models are stretching the 
upper level trough over the northeast Pacific further south off the 
central California coast...slowing its eastward progress. This will give less 
onshore flow and upper ridge development...giving US less warming 
than earlier thought over the weekend. Likens 


Long term...no changes. Previous discussion follows...medium range 
models develop an upper level low off the California coast Monday and 
begin moving it onshore Monday evening. At this time the models are 
keeping the convective activity south and east of the area...but with 
the variability in the model solutions this will have to be watched. 
Models shift an upper level trough over the forecast area Tuesday 
night and maintain its position over the area through middle week with 
weak disturbances moving through the flow. The models are having a 
bit of trouble locking onto this pattern and vary a lot in the timing 
and strength of the disturbances. Will continue a dry forecast with 
increasing onshore flow and clouds for the middle of next week. 


&& 


Aviation...deep marine layer in place this morning with marine 
stratus along the coast...in the coastal gaps...and across inland 
areas north of ksle. Per observations and satellite imagery...the 
average base of the marine stratus is about 2k feet...with tops 
reaching about 3k feet. Local studies suggest stratus will become 
scattered at kpdx around 19z...and 20-21z for areas further west 
along the Columbia River. Given the pattern has not changed much 
over the last couple of days this seems very reasonable. At the 
coast expect MVFR ceilings to prevail through about 20z in the south 
with little to no breaks expected in the north...similar to 
yesterday. All coast returns to MVFR ceilings by 05z...with interior 
sites north of ksle garnering MVFR ceilings around sunrise Friday. 


Pdx and approaches...MVFR ceilings around 2500 feet will continue through 
18z. From 18-20z expect ceilings to transition from broken to 
scattered...eventually clearing out completely by the afternoon. Tonight 
should be a Carbon copy of last...so expect MVFR ceilings to return to 
kpdx 10-12z Friday. Dalton 
&& 


Marine...fairly calm winds across the coastal waters this morning. 
This will change by early this afternoon. Will see small craft winds 
creep up in the southern waters...mainly inside of buoy 50. 
Additionally...winds will also hit Small Craft Advisory criteria in zone pzz270 this 
evening. Seas will be wind driven with a relatively short period of 
7-8 seconds. On Saturday...toned down the winds a little bit. 
Surface pressure pattern on Sat afternoon should only support Small Craft Advisory 
winds in the near shore waters south of Cascade Head. Dalton 


&& 


Pqr watches/warnings/advisories... 
or/WA...Small Craft Advisory for winds Cascade Head to Florence 
through early Sat morning. 
Small Craft Advisory for winds Cape Shoalwater to Cascade 
Head this afternoon and evening. 


&& 


Preliminary point probability of precipitation (probability of measurable precipitation) 
AST 2---- pdx ----- sle ----- eug ----- 


$$ 


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.