It’s been a common saying in the Willamette Valley (including Portland) that you don’t need air conditioning in our climate. I’ve been hearing that since the 1970s when I was a kid. After the past two summers, many would disagree now.
Last summer we set a record for most nights above 60 degrees here in Portland…44!
Well here we are on August 28th, and now we’ve seen 40 such warm nights this summer so far. I think it’s quite likely we’ll see 5 more between now and the end of September so we’ll probably set a new record for a 2nd year.
So what’s causing this? One thing that isn’t…plenty of these nights have been under perfectly clear skies, so it’s not as if we’ve been seeing lots more cloud cover at night. That would sure raise overnight lows.
More likely it’s a combination of the both the urban heat island effect and our warming summers.
I can’t speak with any knowledge on the first because I haven’t check outlying areas (like Aurora, Battle Ground, Sandy etc…) to see if they have seen a similar rise in overnight temps. Common sense would tell you that overnight temps in summer in a rapidly growing metro area should warm; although PDX isn’t exactly surrounded by concrete and buildings. You can see the increase in warm nights since 1941
As for the warming summers…our summers have definitely been warmer, check out the June-August temps for the lower elevations of western Oregon. That’s Oregon climate zone #2. It’s also interesting that summers seemed to cool from around 1955 to 1980, then warm again following. With warmer summers, one would expect both warmer daytime highs and warmer nights.
Will this continue? History would say we will be in unprecedented territory if we had a THIRD summer of 35-45 warm nights. Looking at that chart you can see we’ve never had more than one or two summers like this before cooling a bit again. So it’s quite possible next summer is more reasonable. But the big picture also shows that in a slowly warming climate there will be more of this in the future…
My advice is to get at least a one-room air conditioner if you live in an urban area. They are more efficient than they have ever been and cheaper than they were 20 years ago!
Chief Meteorologist Mark Nelsen