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fxus66 kpqr 172125 
afdpqr 


Area forecast discussion 
National Weather Service Portland or 
225 PM PDT Wednesday Mar 17 2010 


Synopsis...high pressure is building quickly into the Pacific 
northwest...bringing drier weather to the area for the rest of the 
week. Brisk northerly flow is developing across Oregon this 
afternoon. Increasing chances for rain develop around the beginning 
of next week as the high pressure system weakens. 


&& 


Short term...satellite imagery shows high pressure building over the 
Pacific northwest with cloud cover diminishing. The upper level flow 
is turning more northerly across the forecast area...resulting in a 
drier air mass with mostly sunny skies over the County Warning Area. 


A very weak upper level trough moves across Oregon tonight...but 
should only bring a few high clouds during the evening. The upper 
ridge then builds in earnest Thursday and Friday across the Pacific 
northwest...with surface high pressure building east of the Cascades. 
This will turn the flow distinctly offshore late in the 
week...bringing dry conditions and plenty of sunshine Thursday 
through Saturday. 


A thermal trough will build up the coast from California...enhancing 
the offshore flow Friday. As a result temperatures could be quite 
warm along the coast Friday. A cooler air mass associated with the 
surface high should keep temperatures in the 60s for the interior valleys...with 
breezy conditions developing near The Gorge and also across the 
higher terrain of the Coast Range. Likens 


Long term...a blocking ridge of high pressure offshore keeping the 
forecast area under very mild conditions will begin to move east 
Sunday as a stronger system approaches the coast late Sunday into 
Monday. This low will effectively break down the ridge and allow 
precipitation to return to the area during the first half of next week. 


&& 


Aviation...VFR tonight and early tomorrow morning with a 
possibility of patchy fog developing in sheltered areas around 
dawn. Otherwise the air mass should be mixed enough to keep fog at 
a minimum. 


Kpdx and approaches...VFR conditions today and tonight. Possible 
patchy fog forming around dawn or just after on Thursday morning...20 
percent chance of MVFR or brief IFR visible. Fog would be short-lived 
with the well mixed air mass. 


&& 


Marine...seas around 14 feet today slowly subside to to 10 to 12 
feet by early Thursday. High pressure builds from the S across the NE Pacific 
today...expanding into the Pacific northwest later this week. This will give 
northerly flow over the waters through the week...with small craft 
wind conditions likely through Thursday night...and possible on Friday. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for winds from 8 PM this evening to 11 PM 
PDT Thursday for coastal waters from Cape Shoalwater Washington to 
Cascade Head or out to 60 nm. 


Small Craft Advisory for hazardous seas until 5 am PDT Thursday 
for coastal waters from Cape Shoalwater Washington to Florence or out 
to 60 nm. 


Small Craft Advisory for winds until 11 PM PDT Thursday for 
coastal waters from Cascade Head to Florence or out to 60 nm. 


Small Craft Advisory for rough Columbia River bar until 9 am 
PDT Thursday. 


&& 


$$ 


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.