News

The science behind Portland's record-breaking heat
Author: PSU Media and Public Relations
Posted: August 21, 2018
It’s official: Portland has broken its all-time record, set in 2015, of 29 days over 90 degrees. Aug. 22 marked the 30th day over 90. July was the the second warmest on record at PDX, and August has been even warmer.
 
The cause of this extreme heat: a series of weather patterns that are conducive to heat in Portland. Near the surface, pressure patterns act to prevent cooling onshore winds from the Pacific Ocean from reaching Portland. Higher up in the atmosphere, a series of warm high pressure systems have bring clear skies and lots of warm sunshine. While the cool Pacific air has never been far away, it just hasn’t been able to reach Portland as often as usual.  
 
We know that human-caused climate change has increased the probability of extreme heat across the globe and also locally. This pattern is illustrated over decades by the number of days each year that are at least 90 degrees at PDX. There is a clear upward trend, although year-to-year variability is large, so this year’s heat isn’t necessarily “new normal” for Portland. Some summers get a lot of weather patterns that cause heat (like 2015, 2017, and 2018), while other summers get a lot of weather patterns that lead to cooler conditions (like in 2010-2013). 
 
As a result, regional hotspots change from year to year, and just because Portland was a hotspot this summer does not mean it will be one next summer. Climate change does, however, make warm patterns warmer and cool pattern less cool. So when we get heat waves, they are now more severe than they were in the past. Similarly, cooler weather patterns are not as cool as they have been in the past.
 
— Information from Paul Loikith, Director of PSU's Climate Science Lab