In my last article, I said that “we’d likely be in for yet another more active-than-normal fire season.” Thus far, that forecast has been a dud, and I couldn’t be happier to have been proven wrong. After the apocalyptic smoke and flames we’ve seen the previous five summers (apart from 2016), why has this summer been so surprisingly pleasant?
The primary reason for our underwhelming fire season was that our summer weather was much closer to climatology, with mild, onshore flow originating from the Pacific and not hot, dry, offshore flow from British Columbia and the rest of the West. Our most recent bad smoke/fire years—2014, 2015, 2017 and 2018—all had over 20 days of highs greater or equal than 85 degrees at Sea-Tac, with 2018 notching a record 32 days. As of 8/21, Seattle only has seen 10 days of 85 or greater, and while we might see a couple more before 2019 is over to exceed our long-term average of 11 days, the chances of us exceeding 15 days is vanishingly small.
Our biggest fire season by far was 2015, where 1,100,000 acres (275 Mercer Islands) of land were scorched in Washington alone. 2017 and 2018 each saw only 1/3 of the acres burnt as 2015, but they were memorable for the insufferable smoke that suffocated the Pacific Northwest. With our persistent onshore flow this summer, almost all the smoke from eastside fires continued moving inland. Our mild summer is evidence of this onshore flow—after all, the Columbia Basin is much hotter than the Pacific Ocean!
Additionally, with the notable exception of the 45,000-acre Williams Flats fire northeast of Grand Coulee Dam, the vast majority of this summer’s wildfires have burned over grass or brush and in easy-to-access locations. Because non-forested locations have far less combustible material, fires there spread more slowly, produce way less smoke, and don’t “jump” from one location to another via smoldering, airborne embers as easily as forest fires. The fact that our fires have been confined to grass and brush and not forests is a testament to the moist fuels compared to the past few years; it’s easier to ignite pine needles than pine trees!
However, I would be remiss to fail to mention the potential for autumn wildfires, particularly over California. As summer transitions to autumn, the giant heat dome over the Rockies and Desert Southwest—and the thermally-induced low pressure associated with it—weakens to the point where pressures inland can be higher than those along the coast, setting up offshore gradients and the dreaded Santa Ana and Diablo Winds. The Camp Fire of 2018 (the deadliest/most destructive wildfire in California history that bankrupted PGandE) occurred in November, and Southern California saw wildfires throughout December 2017. By November and December, the Pacific Northwest is usually getting pummeled with storms off the Pacific, but we’re still definitely susceptible to smoke from fires throughout the West for the next 1 ½ months.
Autumn fire potential notwithstanding, it’s awesome that we had such a mild, smoke-free summer after the truly hellish summers of 2017 and 2018. Here’s hoping our good luck continues through the rest of the year!
Charlie Phillips, a Madrona resident, received his B.S. in atmospheric sciences from the University of Washington and works in Portland as a meteorologist. Check out his weather website at charlie.weathertogether.net.