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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Saturday
• 
• High: 61 °
• Low: 45 °
• Rain

• Sunday
• 
• High: 59 °
• Low: 45 °
• Rain

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

• Tuesday
• 
• High: 55 °
• Low: 39 °
• Chance of Rain

• Wednesday
• 
• High: 57 °
• Low: 39 °
• Chance of Rain

Area forecast discussion 
National Weather Service Portland or 
859 am PDT Sat may 25 2013 


Synopsis...it appears cool and wet conditions will linger across 
southwest Washington and northwest Oregon for much of the Memorial 
Day weekend. Broad upper level low pressure will linger across 
southwestern Canada and the northwestern United States for the next 
several days...with a series of disturbances bringing occasional rain 
to the forecast area. The next weak low pressure system will bring an 
increasing chance for rain as today progresses...with steady rain 
likely throughout the district tonight and early Sunday before 
tapering to showers later Sunday afternoon. A stronger system should 
spread more rain across the district Monday...possibly along with a 
brief period of breezy conditions along the coast. Brisk westerly 
flow will keep things unsettled with rain at times into midweek. 


&& 


Short term...still a few isolated showers in the SW Washington 
foothills and Cascades this morning...otherwise most areas have a mix 
of lingering lower level clouds from overnight stabilization and 
additional low-to middle level cloudiness filling in from offshore. 
Onshore flow is picking up again with the region under upper level 
cyclonic flow...and areas in the south through Lane County can 
expect more clouds to roll in through the morning and early 
afternoon. High pressure at the surface and upper flow becoming more 
north-south should slow the progression of next system and will back 
off on the probability of precipitation a bit for the valley eastward with the morning 
package. Expect another round of rain overnight with precipitable water values up 
around 0.9 in which is above the 75th percentile level for may...or 
about 130-150% of normal. Will likely bring categorical probability of precipitation in for 
most areas late this afternoon into the overnight which current 
forecast has captured well from about Salem south. Kmd 


Rest of the forecast discussion unchanged...weak isentropic lift out 
ahead of an approaching weak low pressure system will cause clouds to 
increase throughout the day. Rain chances will increase along the 
coast by afternoon and inland by this evening. Today may be the 
warmest of the next few...especially near Eugene where some sunshine 
may warm temperatures into the middle to upper 60s. 


The weak low will move onshore overnight tonight. Weak flow pattern 
will result in minimal orographics...and little to no rainshadowing 
for the Willamette Valley. 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. 


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 we are starting to suspect temperatures may again 
have a hard time getting out of the 50s Sunday in a very cloudy and 
wet day. 


Precipitation will taper off as this system moves east sun evening... 
just in time for 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. As 
a result this system may try to split somewhat as it moves onshore... 
but still should hold together enough for a decent rain Memorial Day. 
The good news is that snow levels will probably remain above the 
passes through the Holiday weekend. Weagle 


Long term...made very few changes for the extended period. General 
model trend remains wet midweek followed by more seasonable weather 
later in the week. Previous discussion follows...models start out in 
good agreement during the extended period Monday night and Tuesday...with a 
trough pushing inland over the West Coast. Most of the energy appears 
headed S of the forecast area towards California. As the northern stream 
appears to remain an open wave...will boost probability of precipitation into likely 
category. Models diverge some later in the week...but keep a common 
theme of shortwaves pushing in in a westerly flow aloft. Will keep 
probability of precipitation relatively high for a system on Wednesday...but then will drop probability of precipitation 
off later in the week as upper heights rise. 


&& 


Aviation...VFR across the region this am. Rain increasing 
offshore and will push to coast later this am...and inland during 
the afternoon. Should see MVFR increasing during the afternoon... 
with widespread MVFR and local IFR conditions after 00z. 
Cascades and higher terrain will be obscured in clouds and 
precipitation. 


Kpdx and approaches...VFR and dry this am. Will have light rain 
returning this afternoon...with ceilings gradually lowering. Expect 
mostly MVFR ceilings...2000 to 2500 feet...by 00z to 02z. 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. One model does show gale force wind 
gusts but it appears to be an outlier at this time. Using a more 
conservative approach yields seas in the 6 to 8 feet range and even 
then primarily wind wave/fresh swell driven. As such will see a 
rapid easing once winds drop off Monday night. Rockey. 
&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...none. 
&& 


$$ 


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.