Your Weather

To update your location please enter your ZIP code, city, state, airport code or country in the field below. Weather by E-mail: Forecast storm alerts. Weather E-Mail Alert Sign Up »

Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 63 °
• Low: 52 °
• Rain Showers

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

• Thursday
• 
• High: 61 °
• Low: 54 °
• Chance of Rain

• Friday
• 
• High: 63 °
• Low: 50 °
• Chance of Rain

• Saturday
• 
• High: 68 °
• Low: 52 °
• Mostly Cloudy

Area forecast discussion 
National Weather Service Portland or 
248 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 to develop across the 
forecast area this afternoon. These will continue into this evening 
then 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...this afternoon through Friday...showers started 
developing across the Coast Range and western Willamette Valley 
around midday...and a few have since broken through the cap around 
650 mb which was initially limiting their development. The cap has 
weakened as the middle-upper level cold pool associated with the upper 
low offshore begins to drift onshore. Echo tops with some of the 
larger cells have exceeded 20 kft...and as a result we are getting 
several reports of thunder and small hail around Salem and in the 
western Tualatin valley. 


Meanwhile convection has been a little more subdued over the eastern 
half of the Willamette Valley...with a good deal of sunshine pushing 
surface temperatures just above 70 degrees. This is well above the convective 
temperature in the lower to middle 60s...so the showers developing over the 
western Willamette Valley will have a Fertile environment to 
strengthen or continue as they move east of Interstate 5. Showers are 
also developing along the Cascades...with surface heating improving 
after being delayed by morning cloud cover. Suspect we will see some 
thunderstorms developing over the Cascades later this afternoon as the air 
mass gets more time to destabilize. 


Based on aircraft soundings it appears both directional and speed 
shear remain rather modest this afternoon...especially in the low-middle 
levels. However there will probably be enough for a few more cells to 
be long lived and stronger for some small hail and gusty wind. Todays 
storms should remain well below severe limits though and most will be 
of the pulse variety. 


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 the region. Not much change into this 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 Coast Range and i5 corridor ending by 03z...but 
threat over the Cascades remains until 06z. 


Kpdx and approaches...clouds increasing as showers develop. Will 
remain VFR this evening...but later will have areas of MVFR ceilings 
forming as marine air fills Willamette Valley. Watch for isolated 
thunderstorms around kpdx Ops area...but best threat lies to the east over 
the Cascades until 06z. Rockey. 
&& 


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...with gusts 25 to 30 knots. Small Craft 
Advisory for these winds until 9 PM...then winds gradually ease. 


SW swell of 5 to 6 feet at moment...then slowly easing back to 4 feet 
Wednesday. Swell will decrease a bit Thursday and Friday as high pressure builds. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for winds until 9 PM this evening for 
all coastal marine waters. 


$$ 


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.