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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Saturday
• 
• High: 57 °
• Low: 43 °
• Rain

• Sunday
• 
• High: 64 °
• Low: 41 °
• Chance of Rain

• Monday
• 
• High: 73 °
• Low: 43 °
• Partly Cloudy

• Tuesday
• 
• High: 59 °
• Low: 37 °
• Chance of Rain

• Wednesday
• 
• High: 54 °
• Low: 34 °
• Chance of Rain

Area forecast discussion 
National Weather Service Portland or 
908 am PDT Sat may 18 2013 


Synopsis...a weak frontal system is spreading light rain across 
forecast area this morning. Occasional rain will continue through the 
day with cloudy skies and temperatures stuck around 60 degrees for The 
Lowlands. Snow levels will remain well above the passes. Showers will 
gradually decrease tonight and Sunday as the system moves into the 
Great Basin and high pressure begins to build. This high pressure 
should result in drier and warmer conditions Sun night into Monday. 
However it appears likely an unseasonably cold upper low will bring 
cool and unsettled weather Tuesday through Friday. 


&& 


Short term...today through Tuesday night...latest radar imagery and 
surface observations show light rain spreading across the Portland 
and Vancouver metropolitan this morning...moving east into the Cascades. A 
weak frontal system moving onshore is responsible for this...with the 
first band of rain associated with weak isentropic lift. 


Latest msas surface pressure analysis shows an elongated low pressure 
trough just offshore...which seems to match visible imagery fairly 
well. Looping this imagery seems to show a very faint circulation in 
the low clouds centered near 46n/126w...moving northeast. This weak 
low will likely drag a weak cold front across the district this 
afternoon...spreading another batch of rain across the forecast area. 
Overall rainfall amounts today through this evening will probably be 
0.10-0.20 inch in the valleys...up to 0.50-0.75 inch in the higher 
terrain. Expect little to no breaks in the clouds today with the very 
moist air mass...temperatures will struggle to reach 60 degrees and MOS 
guidance appears to be catching on to this concept. 


There will be more breaks in the clouds Sunday as high pressure 
begins to build into the region. Some weak and shallow instability 
left behind by allow an isolated shower or two...with the best chance 
over the higher terrain. The air mass will be rapidly warming 
aloft...capping the instability and keeping it too shallow for thunderstorms 
Sunday despite the warmer surface temperatures in the middle to upper 60s. Weagle 


Remainder of forecast discussion unchanged from previous shift...high 
pressure maintain dry weather for Monday which will likely be 
the warmest day of the week. Increased sunshine should warm interior 
temperatures to slightly above normal...low 70s and coastal areas to 
near normal...lower 60s. An upper level low will approach Monday 
night and bring a return of showers and much cooler weather to the 
region. Models have backed off the timing of the onset of rain around 
12 hours. The coldest air associated with the low will begin moving 
over the area Tuesday night and snow levels should lower to around 
3500 to 4000 feet. 


Long term...Wednesday through Friday...a cold closed low will 
continue unsettled weather with unseasonal cold temperatures 
Wednesday...with record low maximum temperatures possible. Wednesday 
will be the coldest day of the work week. Temperatures will remain 
below the seasonal normals Thursday and Friday as a couple of 
shortwave troughs will continue showery and cool conditions. 


&& 


Aviation...a frontal boundary moving through the region will 
bring periods of light rain or showers through much of the day. 
Expect a mix of VFR and MVFR conditions...with the periods of MVFR 
coinciding with the heavier showers. Expect shower activity to 
continue but become more scattered this evening behind the frontal 
passage. Expect mainly VFR conditions this evening...with MVFR 
ceilings pushing into the coast overnight. 


Kpdx and approaches...expect light rain or showers off and on 
through the day. Predominantly VFR conditions may drop to MVFR at 
times during heavier showers. Shower activity should taper off 
somewhat this evening...with mainly VFR conditions during the 
evening and overnight hours. Pyle 


&& 


Marine...a front will push across the coastal waters this 
morning...then inland early this afternoon. Not a lot of wind 
currently being observed...but expect that winds will pick up a 
bit later this morning as the cold front comes through. There 
seems so be enough gradient to pop gusts 20 to 25 knots right ahead 
of the front. So will maintain current Small Craft Advisory. 
Otherwise...winds turn west to northwest behind the front in the afternoon 
and begin to ease. 


High pressure will build over the NE Pacific sun into early next week. 
This will keep northwest winds 10 to 15 knots through much of the coming 
week...though may briefly get 20 to 25 knots gusts Monday afternoon into 
the evening. 


Seas remain at 5 to 6 feet for into early next week. May see seas 
build up and become choppy at times with the brisk northwest winds on the 
central Oregon coastal waters next week. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for winds until 3 PM PDT this afternoon for 
coastal waters from Cape Shoalwater Washington to Florence or out 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.