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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 45 °
• Low: 34 °
• Rain Showers

• Tuesday
• 
• High: 45 °
• Low: 34 °
• Rain

• Wednesday
• 
• High: 49 °
• Low: 38 °
• Chance of Rain

• Thursday
• 
• High: 50 °
• Low: 40 °
• Rain

• Friday
• 
• High: 50 °
• Low: 40 °
• Rain

Area forecast discussion 
National Weather Service Portland or 
239 am PST Monday Feb 13 2012 


Synopsis...an elongated upper trough continues to bring widespread 
light rain and mountain snow to the district this morning. 
Precipitation will gradually taper off this afternoon and evening as 
most of the energy heads south into California and a Flat Ridge of 
high pressure builds across Oregon and Washington. However the next 
system will come in quickly from the northwest Tuesday bringing more 
showers and possibly snow down to the foothills. After another break 
on Wednesday the weather appears to become gradually more active as 
we head into next weekend. 


&& 


Short term...satellite water vapor imagery shows an elongated upper 
level trough over the western United States and Canada...with a 
strong punch of jet energy entering the base of the trough near the 
northern California coast. This will eventually cause an upper low to develop 
and cut off from the main upper trough as it drifts into northern 
California today. Meanwhile...steady light rain and mountain snow 
continues mainly due to deformation along the upper trough axis. This 
will continue through the morning then gradually taper off this 
afternoon and evening as the upper low over California becomes more dominant 
and the northern upper trough moves east of the Cascades. 


Temperatures suggest snow levels around 1500-2000 feet in the Coast 
Range and 2000-2500 feet in the Cascades this morning. Widespread 1-3 
inch accumulations are likely in steady light snow above these 
elevations...not likely enough to warrant an advisory. Snow levels 
likely remain around the same all day with precipitation tapering off 
from north to south as the day progresses. 


Some very gradual clearing is possible Monday evening...but if this 
occurs it probably will not take long for patchy low clouds and fog 
to form. Some valley locations may flirt with freezing temperatures Tuesday 
morning. 


The next system is expected to move in from the northwest Tuesday. 
Snow levels will again be on the lower side...perhaps a little lower 
than those today. The European model (ecmwf) has been the most consistent model... 
with the GFS the least consistent model. Probability of precipitation have been bumped up to 
likely but no higher yet until a bit more model and run-to-run 
consistency is achieved. This system moves south by Wednesday and we 
have a decent chance at a break on Wednesday before the next system 
Thursday. Weagle/Tolleson 


Long term...no changes. Previous discussion follows...plenty of 
uncertainty remains in the extended forecast...as progressive split flow 
is expected to continue. However...the models are beginning to 
converge on a solution that brings another brief shot of rain on Thursday 
as a frontal system drives through the top of the ridge through 
BC/Washington. Going into the weekend...models again diverge. The one 
thing they can agree on is that we will continue to remain in a 
progressive winter time pattern...with the potential for a couple of 
systems to impact the Pacific northwest. Kept probability of precipitation above climatology through the 
weekend. Jfp 


&& 


Aviation....as light rain and drizzle continues this morning 
expect to see widespread MVFR conditions. Conditions will turn 
more showery by 18z with VFR becoming dominant after 22z. 


Kpdx and approaches...MVFR conditions in light rain and drizzle 
will continue this morning. The precipitation will turn more 
showery after 17z with VFR becoming predominant after 19z. 


&& 


Marine...northwest winds will rise this morning as high pressure builds 
toward the coast. Gale force wind gusts still look possible this 
morning over the southern outer waters...while the rest of the 
area sees winds peaking in small craft category. Winds in the 
northern inner waters may stay below advisory criteria as the 
strongest gradients remain offshore and south. Seas will also 
rise today as a westerly swell train arrives...with wave heights 
expected to reach the low to middle teens late today and tonight. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Gale Warning until 10 am PST this morning for waters from 
Cascade Head to Florence or from 10 to 60 nm. 


Small Craft Advisory for winds until 6 PM PST this evening for 
coastal waters from Cascade Head to Florence or out 10 nm- 
waters from Cape Shoalwater Washington to Cascade Head or from 10 
to 60 nm. 


Small Craft Advisory for hazardous seas until 6 PM PST Tuesday 
for coastal waters from Cape Shoalwater Washington to Cascade Head 
or out 10 nm-coastal waters from Cascade Head to Florence 
or out 10 nm-waters from Cape Shoalwater Washington to Cascade Head 
or from 10 to 60 nm. 


Small Craft Advisory for rough bar from 6 am this morning to 6 
am PST Tuesday for Columbia River bar. 


&& 


$$ 


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.