With a record number of days reaching 85 degrees, Seattle recorded one of its hottest years in 2018. That's consistent with recent trends.
Looking back at the past 70 years of temperature records in the Seattle area, this decade is beginning to stand out in stark terms.
Seattle finished 2018 with an average high temperature of 62.3 degrees, making it the fifth-hottest year on record in data going back to 1948 at the Seattle-Tacoma International Airport. The only warmer years were 2015 (63.4 degrees), 2014 (62.6 degrees), 2016 (62.5 degrees) and 1992 (62.5 degrees).
So why are so many years from this decade crowding the top of the records books?
Washington State Climatologist Nick Bond said there are two things going on. First, Bond said, there’s no question that the weather data from recent decades shows a baseline warming trend that’s reflective of global climate change that scientists largely attribute to human activities that emit heat-trapping gasses.
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The data from the National Climatic Data Center shows the average high temperature in the area was about 58 degrees in the 1950s. It has climbed steadily. And, this decade, the average high is so far surpassing 61 degrees. (Note: We compiled this year’s weather from a combination of records from the National Climactic Data Center, which collects the historical data, and some preliminary local records from the National Weather Service because the national data center’s site is now shuttered because of the federal government’s shutdown.)
Bond said that along with the overall global warming, the last few years in the Seattle area have also been particularly hot. He said climate trends can sometimes develop multiyear warming or cooling periods.
“We’re in a relatively warm period, and so when that is on top of this overall warming trend, it means a disproportionate number of record years are recently,” Bond said.
Bond said it’s possible that the coming years could show some temperature moderation or cooling. But, for now, Seattle residents are getting a taste of what a warming climate could make the norm in the longer term.
In 2018, the area set a record of 32 days that reached at least 85 degrees, surpassing the 2017 record of 27, and well above the average of about 11. We reached 90 degrees on 11 days, second only to 2015’s 12 days. That’s left people in Seattle, the least air-conditioned metro in the United States, exploring creative solutions to keep cool in the summer.
Bond also noted that average temperature lows have risen over the years. This year, we had 22 days that never got below 60 degrees. That ranks as the fourth-most in the data. All of the top five years were from this decade.
Seattle also had a comparatively dry year, recording less than 36 inches of rain, below the average of about 39 inches. That was, in large part, because of the parched summer. From the start of May through August, Seattle logged just 1 inch of rain. The next driest May-August period on record was 2003, with 2.05 inches.
Bond said one wrinkle to consider about this year’s data was the period of summer wildfire smoke. Those hazy days likely kept a lid on high temperatures, so the days were cooler than they could have been otherwise.
More wildfire smoke is just one of the many climatic events that could result from the overall warming climate. A federal report this year projected that the Northwest could also see both more drought and more extreme rain events.
The report warns that if emissions are left unchecked, salmon could see shrinking habitat from warming stream waters, revenue from skiing and snow-based recreation could drop, and farmers who are already dealing with changes would see additional negative effects.
In the nearer term, forecasters believe the coming months in the Seattle area will likely be warmer than normal. Bond said that has to do with some El Niño conditions, with warmer-than-normal waters in the tropical Pacific.