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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Saturday
• 
• High: 66 °
• Low: 50 °
• Rain

• Sunday
• 
• High: 63 °
• Low: 48 °
• Rain

• Monday
• 
• High: 59 °
• Low: 50 °
• Rain

• Tuesday
• 
• High: 61 °
• Low: 48 °
• Chance of Rain

• Wednesday
• 
• High: 61 °
• Low: 46 °
• Chance of Rain

Area forecast discussion 
National Weather Service Portland or 
200 PM PDT Sat may 25 2013 


Synopsis...after a break in rain this afternoon...upper level low 
pressure brings a wave of rain tonight...lingering into Sunday before 
tapering to showers later Sunday afternoon. A stronger system should 
spread more rain across the district on Memorial Day...possibly along 
with a brief period of breezy conditions along the coast. Brisk 
westerly flow will keep things unsettled with rain at times through 
at least middle week. There is a hint that we may dry out by next 
weekend. 


&& 


Short term... tonight through Tuesday...our main feature of interest 
is the upper disturbance pushing inside 130 west around 46 north this 
afternoon...as the upper low off Puget Sound sound remains stationary 
through the evening. The main energy associated with this disturbance 
will push south of the area...but enough will be left to bring a 
round of widespread rain as these systems amalgamate into one mean 
upper trough. Low to middle level warm advection in the SW flow ahead of 
the low as increased the cloud shield offshore and into SW 
Washington...while surface high pressure...now weakening...has kept 
this system from making much inland progress elsewhere. Rain has now 
finally pushed into Astoria. 


The first low/disturbance will move onshore overnight tonight. Weak 
flow pattern will result in minimal orographics...and little to no 
rainshadowing for the Willamette Valley. Additionally...precipitable water values are 
up around 0.9 in which is above the 75th percentile level for 
may...or about 130-150% of normal. So again there could be a good bit 
of steady rain in The Lowlands tonight into Sunday morning. Not 
expecting the same kind of totals we experienced around Portland the 
last few days...but this will probably be a heavier event for Salem 
and Eugene who received less precipitation from the last couple of systems. 


The upper low will very slowly progress through the area on 
Sunday...thus expect lingering clouds and rain...with additional 
energy associated with the low off the Puget Sound sound prognosticated to swing 
through in the afternoon and evening. There is a bit of 
question as to whether rain will be steady or more showery Sunday 
afternoon as the associated upper low moves onshore. NAM bufr 
soundings show a very moist air mass but little in the way of 
instability. Regardless temperatures may again have a hard time getting out 
of the 50s Sunday to near 60 in a cloudy and wet day...though they 
may spike later in the afternoon in any sunbreaks...as overnight 
lows will not drop much tonight given clouds spreading in. Kept the 
middle-shifts trend to keep temperatures several degrees below guidance 
but did nudge them up a touch. Anywhere that sees a few sunbreaks 
will warm a bit more into the 60s with the warm late may sun...with 
the best chance in Lee of the Coast Range and for areas southwest 
where more ridging attempts to build in. 


The upper trough will still be working its way through the northern 
tier Sunday evening...thus some lingering rain/showers mainly before 
midnight. Precipitation will taper off elsewhere as this system moves 
east sun evening...as high pressure noses in from the southwest 
through the afternoon. Should be a bit of break Sunday evening from 
southwest to northeast...though some rain/showers may linger in the 
northern tier as the upper low continues to pass through. The break 
will unfortunately be short lived...as a more organized Pacific 
frontal system to move onshore later Sunday night or Monday/Memorial 
Day morning. Depending on the track of this system it may have a 
brief punch of modest coastal wind with it...but this appears more 
likely for southern Oregon or northern California where the best jet 
dynamics will be. The surface pattern looks such that will remain 
offshore for quite some time...keeping the strongest winds confined 
to the coastal waters. As a result this system may try to split 
somewhat as it moves onshore... but still should hold together enough 
for another pretty good soaking Memorial Day. The upper trough 
lingers in the area for Tuesday meaning cloudy and periods of 
rain/showers. Kmd 


Long term...Tuesday evening through Saturday...cool and showery 
conditions will continue through much of the work week as several 
shortwaves wrap around a broad upper level trough. An upper level 
ridge attempts to build over the Pacific northwest by Friday and 
early next weekend. This should dry out the conditions over the 
region starting late Thursday night and Friday...allowing snow 
levels to rise and temperatures back near normal. Granted there have 
been decent model discrepancies concerning this potential 
ridging...but seems like we could see ridging lingering through next 
weekend. /27 




&& 


Aviation...VFR across the region will transition back to MVFR 
this afternoon on the coast...and this evening further inland. This 
due to increasing rain as yet another front now about 200 miles 
offshore pushes inland. Widespread MVFR across region tonight and 
into sun am... with local IFR conditions after 03z on the coast. 
Cascades and higher terrain will be obscured in clouds and precipitation. 


Kpdx and approaches...VFR and dry until later this afternoon. 
Clouds will thicken after 22z...with occasional rain after 00z. 
Still looks likely that ceilings will gradually lower. Expect mostly 
MVFR ceilings...2000 to 2500 feet...after 04z. Little change expected 
tonight with MVFR ceilings dominating. Rockey. 
&& 


Marine...front approaching...but gradient not impressive. Will 
keep south winds 10 to 20 knots...but can not rule out a few gusts to 
25 knots. Not enough to warrant any advisories. Front will push 
onshore early sun am...with winds relaxing. Seas mostly 5 to 7 feet 
though sun evening. 


Another front arrives Sun night and Monday. Appears that solid small 
craft winds of 20 to 30 knots. Seas may briefly clip 10 feet on Monday due 
to combined seas...but drop back Monday night as wind eases. Rockey. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for rough Columbia bar conditions from 
from 5 am to 9 am sun. 
&& 


$$ 


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.