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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Friday
• 
• High: 70 °
• Low: 48 °
• Chance of T-Storms

• Saturday
• 
• High: 70 °
• Low: 52 °
• Chance of Rain

• Sunday
• 
• High: 63 °
• Low: 45 °
• Chance of Rain

• Monday
• 
• High: 64 °
• Low: 36 °
• Mostly Cloudy

• Tuesday
• 
• High: 72 °
• Low: 39 °
• Mostly Cloudy

Area forecast discussion 
National Weather Service Portland or 
901 PM PDT Thursday may 24 2012 


Synopsis...an upper low will drift southward into California later 
tonight and early Friday...but may remain close enough to feed some 
moisture north into our forecast area for a few showers or 
thunderstorms again on Friday and Saturday. Onshore flow and a weak 
system may spread some light rain onshore again Sunday. A weak system 
will brush the area on Memorial Day to keep a few showers around 
especially north...then a brief break is possible as a weak ridge 
builds in. 


&& 


Short term...a loop of radar imagery reveals a general weakening in 
shower activity across western Oregon and Washington this evening as 
surface based instability wanes. This trend should continue across 
much of the County Warning Area over the next couple of hours. Rain showers will 
likely hold on longest across the central Cascades and foothills 
where colder temperatures aloft and northerly low to middle level flow 
will allow meager orographic ascent. A few showers will likely move 
westward into the southern Washington Cascades overnight...but expect this 
activity to weaken considerably as it tries to enter the lower 
Columbia/Willamette River Valley. Main grid edits were to probability of precipitation and 
sky cover overnight to try and reflect the latest trends. /Neuman 


Previous discussion follows...snow levels will remain near the passes 
in the Cascades tonight...but any significant accumulations will be 
above 5500 to 6000 feet. 


Energy from the upper low rotates back north into central and eastern 
Oregon on Friday and looks as though it will rotate back into at 
least the Cascades and possibly into the valley and east slopes of 
the Coast Range on Friday afternoon and evening for a few showers or 
even a thunderstorm. With more breaks in the clouds and some sunshine 
expected on Friday afternoon...this in combination with a slowly 
warming air mass should allow temperatures to get closer to normal on Friday 
as well as contribute to the convective potential. 


The upper low wobbles around and lingers into Saturday and begins to 
lift out through Idaho later Saturday. Enough energy remains for some 
convection to again wrap back into the Cascades and possibly into the 
valleys again Saturday afternoon and evening. The models are showing 
a lot of onshore flow and clouds west of the Cascades on Saturday and 
it may take a while for the clouds to break out. 


Then finally...the models continue to show a weak front approaching 
the coast Saturday night and moving onshore Sunday. The GFS model is 
the strongest...and European model (ecmwf) the weakest. Sunday is looking about 5 or 
so degrees cooler than Saturday with more clouds and a little light 
rain possible. Tolleson 


Long term...cool and cloudy conditions start off the extended period 
Sunday evening. Models continue to show a few light showers and below 
normal temperatures to persist into Monday as an upper level trough 
moves over the region. Very weak ridging develops around 
Tuesday...but model discrepancies become more apparent by middle week. 
The European model (ecmwf) and the Gem attempt to keep the area damp and cool as 
disturbances move through the area. The GFS strengthens and amplifies 
the previously weak ridge...keeping it over the area through the end 
of the week. Nevertheless...have maintained a slight chance for 
showers and near normal temperatures through late next week due to 
low confidence in model guidance. 27 
&& 


Aviation...showers continue across the area this evening though 
have diminished in coverage and intensity. Do not expect any 
further thunderstorm threat overnight tonight. Expect mainly VFR 
conditions through the night...with local MVFR conditions under 
diminishing showers. 


As the low continues to dive south tomorrow...another round of 
deeper convection is possible mainly in the afternoon for the 
inland locations. Flow will likely turn and become more from the 
north to northeast with some potential to see storms initiate over 
the Cascades and foothills then track over the Willamette Valley. 


Kpdx and approaches...VFR ceilings will continue through the night as 
shower activity decreases. Depending on the amount of 
clearing...may see local IFR ceilings form toward morning... 
after 08z-10z. Brown 


&& 


Marine...not much change made to the marine forecast this 
evening. Small craft wind conditions can be expected across the 
southern outer waters overnight tonight and through the day 
Friday...mainly seen in the gusts. Seas generally remain in the 
6 to 8 feet range through Friday then drop off dramatically heading 
into the weekend. Brown 




&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for winds until 2 am PDT Saturday for 
waters from Cascade Head to Florence or from 10 to 60 nm. 


&& 


$$ 


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.