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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 63 °
• Low: 52 °
• Rain

• Thursday
• 
• High: 61 °
• Low: 52 °
• Rain Showers

• Friday
• 
• High: 68 °
• Low: 43 °
• Chance of Rain

• Saturday
• 
• High: 72 °
• Low: 43 °
• Mostly Cloudy

• Sunday
• 
• High: 77 °
• Low: 54 °
• Chance of Rain

Area forecast discussion 
National Weather Service Portland or 
838 PM PDT Tuesday Jun 18 2013 


Synopsis...an upper level low just off the Pacific northwest coast 
is causing showers and even a few thunderstorms this evening. 
These will slowly diminish overnight. Wednesday will be cool and 
cloudy with occasional rain...with the thunderstorm threat likely 
limited to the Cascade crest eastward. Showers will only gradually 
taper off Thursday and Friday as the upper low lingers over eastern 
Washington. The weekend warmup is looking less likely with recent 
model runs...in fact some models are bringing in a Pacific frontal 
system for more 
rain. 


&& 


Short term...a broad area of showers extends over the South 
Washington...north Oregon and Lane County Cascade foothills and 
western Columbia Gorge at 830pm. These showers will continue to move 
east. There are also a few showers popping up elesewhere such as 
ones over Vancouver Washington. The atmosphere will stabilize some 
in the lower levels overnight...but will still remain unstable 
enough under the influence of the upper low and increasing cooling 
aloft...for isolated showers such as these overnight. There will 
continue to be a slight chance of thunderstorms in the north Oregon 
and South Washington foothills and Cascades until after midnight but 
without a strong lifting mechanism such as a shortwave...the models 
indicate that the threat of thunderstorms is minimal elsewhere 
overnight. Schneider 


Unseasonably cool...cloudy and damp weather is likely for Wednesday 
as the upper low drifts east across the State of Oregon. Confidence 
is growing that precipitation will be more steady and stratiform 
across most of the forecast area...with convection limited to the 
Cascade crest eastward. NAM cross sections show broad low-middle level 
lift within a very moist layer...also indicative of more stratiform 
precipitation. Any sun breaks could provide more of a convective nature to 
the precipitation...but at this point it appears sunbreaks will be very few 
and far between if any Wednesday. 


By Thursday models start to diverge on what the upper low does. The 
trend has been for slower movement of the system...with it lingering 
somewhere over the middle-Columbia Basin Thursday and possibly Friday. 
With this proximity there will be the continued threat of wraparound 
moisture and showers...most prolific on the 12z GFS and Canadian 
models. Adjusted probability of precipitation upward for these days as models seem to be 
hanging on to the shower threat longer than earlier runs. Weagle 


Long term...Friday night through Monday...given the last couple of 
model runs we are starting to lose confidence in our weekend ridging 
and warmup. The upper low festering over the middle-Columbia Basin now 
appears to linger into Friday...not really allowing the upper ridge 
to build in full force before the next Pacific frontal system 
approaches for the weekend. There are a couple factors to consider 
here. There is a historically strong upper level ridge over Alaska... 
with our upper low stuck below it in a Rex block pattern. The 
tendency will be for the Pacific jet to try to undercut the alaskan 
ridge this weekend and this is what the models are beginning to show. 
Additionally the Madden-Julian oscillation seems to be entering its 
most active phase since February...which is impressive for June. All 
this points to a wet week next week...so we significantly trended 
probability of precipitation upward and cooled off temperatures beginning Sunday. Weagle 


&& 


Aviation...predominately VFR across the region...with lots of 
showers around. Not much change through the evening...but will 
see clouds increasing across the region tonight as onshore flow 
begins increasing. Clouds not solid offshore...but still looks 
like MVFR with pockets of IFR on coast later tonight...with 
increasing low VFR and high end MVFR clouds inland. Isolated 
thunderstorms over the Cascade foothills ending by 05z. 


Kpdx and approaches...will remain VFR this evening...but later 
will have areas of MVFR ceilings forming as marine air fills 
Willamette Valley. Isolated thunderstorms around kpdx Ops area through 
05z. 


&& 


Marine...little change as a broad area of low pressure offshore will 
continue to slowly track toward the coast through Wednesday. Winds 
generally 15 to 20 knots this evening...then easing overnight. 
Seas will remain well below 10 feet through the week. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...none. 
&& 


$$ 


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.