Wednesday, September 23, 2020

Smoky siege: A look back at the smoke storm of 2020

The record-shattering smoke storm of 2020 is now behind us. Rain clouds have replaced the choking fog of smoke that held Washington in a vice for more than a week, and the annual dread of late-summer wildfires appears to have eased. 

Before we get back to business as usual, however, we wanted to review what exactly happened in the first three weeks of September, what it did to all of us that were stuck breathing that toxic soup, and what we can learn from this smoke event to prepare us for future summers when the smoke returns.


For most of the summer of 2020, the Pacific Northwest enjoyed a mild wildfire season. The major impacts to air quality were a few fast-burning range fires near Yakima and Mattawa.

In the late August and early September, increasingly hot and dry conditions set the stage for what was to come. As Labor Day weekend arrived, so did the fires. The tiny town of Malden near Pullman was nearly destroyed by a fast-moving blaze, and a 1-year-old child died as his parents fled the Cold Springs Fire outside of Omak. 

On Labor Day, Sept. 7, the typical onshore flow of wind and weather systems moving in from the ocean shifted as high pressure built up over the interior northwest and low pressure set up along the coast. Since winds blow from high pressure toward low pressure areas, they began to blow from the east and strengthened quickly. 

In Washington, winds up to 50 miles per hour pushed smoke from the fires to the east across the mountains and into the cities of the Puget Sound region. Ash fell around Seattle, and the air took on the smell of a campfire.

On Sept. 8, air quality declined to unhealthy levels in the Puget Sound region. South of Seattle, a brush fire leapt up in the Tacoma suburb of Bonney Lake, destroying two homes and forcing thousands of residents to evacuate.

The situation in Oregon was much more dire. Wildfires exploded in southern, central and northern Oregon, forced the evacuation of entire cities, ultimately burning up to the edges of the Portland suburbs as nearly a million acres of forest and hundreds of homes succumbed to the flames.

A “super massive” plume

Smoke from these fires settled off of the Oregon coast, where the cool waters finally calmed the winds. Over the week of Sept. 6, the smoke built up into a super-massive plume – a ghostly echo as large as the state that spawned it.

At the Washington Department of Ecology, smoke forecasters watched this plume build with unease. Off the coast, the choking cloud of smoke posed little danger to Washington communities, and lighter winds were forecast with the potential to blow the smoke north, skirting the Washington coast and heading into Canada.

If the typical onshore flow were to return, however, the smoke would circle around the Olympic Mountains and crash into Seattle, threatening more than 4 million people in the city’s metropolitan area.

On Thursday, Sept. 10, the hope that Washington would dodge the bullet faded. Winds shifted to southwest, pushing the smoke toward western Washington.

The heat from wildfires can drive smoke high into the atmosphere, where winds can pick that smoke up and drive it hundreds or thousands of miles. That wasn’t the case this time. Cooler temperatures the night of Sept. 10 allowed the smoke to mix down to ground level, and western Washington awoke on Friday, Sept. 11, to ashen skies.

The super massive plume continued to creep across Washington through the weekend, subjecting first central and then eastern Washington to the thick smoke. Had the smoke simply continued to blow eastward, however, it would have gradually cleared out and allowed air quality to recover.

That didn’t happen.

Forecasting smoke is not like conventional weather forecasting. Wildfires can grow suddenly, unleashing fresh torrents of smoke and ash. New fires can pop up, or firefighters can gain or lose ground on existing fires. Smoke rises and falls during the day, driven by wind and temperature changes.

Because of these complexities, the same sort of sophisticated computer model that confidently predicts rain a week ahead of time struggles to accurately forecast smoke more than a day or two out. Smoke forecasters use their personal expertise to try to out-guess the computer models, but they, too, are sometimes caught off guard as wind and weather combine to frustrate their expectations.

“What do you do when the atmosphere doesn’t deliver what you ordered?” asked Dr. Ranil Dhammapala, an atmospheric scientist and smoke forecaster with Ecology. “You try to diagnose the problem, take into consideration the lessons learned and issue an updated forecast.

“We look at multiple weather and smoke models, each with their own strengths and weaknesses,” Dhammapala said. “We also consider feedback from other forecasters, wildland fire managers and look at monitoring data continuously. Forecasts are constantly recalibrated as new information becomes available.”

The night of Sunday, Sept. 13, such a recalibration proved necessary. The wind working to clear the plume faltered. A new, weak front was forecast to continue the clear-out, but those winds instead sailed mostly overhead.

Why? With no wind and a thick blanket of smoke over the entire state, little sunlight reached the surface, meaning there was none of the usual daytime warming that produces evening breezes. Just as it does during wintertime temperature inversions, the smoke settled in the valleys and basins of Washington, forcing millions of residents to shelter inside.

A dark cloud

As that smoke settled, air quality grew worse and worse.

Between Saturday, Sept. 12 and Thursday, Sept. 17, every single air quality monitor in Washington state recorded levels of particulate pollution above the federal 24-hour standard.

Particulate pollution, especially the tiny particles known as PM2.5, pose a serious threat to human health. PM2.5 particles are 2.5 micrometers or smaller in size - so small that our bodies’ natural defenses don’t work against them. They lodge deep in our lungs and even get into our bloodstreams.

Short-term exposures to PM2.5 can irritate your eyes and throat, produce headaches, and leave you short of breath. For people who already suffer from a respiratory illness or heart disease, the effects are worse, and can be life-threatening.

“It’s very clear from research done here in Washington and in other places that more and more of the population suffers certain health problems when there’s a lot of wildfire smoke,” said Dr. Matt Kadlec, Ecology’s smoke toxicologist. “It’s common for people to have eye and respiratory tract irritation; stress; headaches; shortness of breath; and, among those who already have asthma, worsened symptoms. As smoke levels increase and last longer, respiratory and cardiovascular health risks increase, resulting in greater incidences of emergency department visits, hospital admissions, and even deaths.”

Washington is no stranger to wildfire smoke. The Carlton Complex Fire in 2014 burned more than a quarter-million acres and destroyed more than 350 homes in the Methow Valley. In 2017 and again in 2018, huge wildfires in British Columbia sent smoke southward, blanketing much of the state for weeks.

As bad as these smoke events were, they could not compare to September 2020.

Ecology scientist Dr. Beth Friedman looked at historical records going back to when the agency began tracking PM2.5 levels in the early 2000s. She found that more Washington cities were exposed to hazardous air quality – the highest category for air pollution – for longer than during any previous smoke event.

“This smoke event marks the most days statewide PM2.5 monitoring sites have recorded hazardous air quality going back to 2000, and the majority of the state experienced at least five consecutive days of very unhealthy or hazardous air quality,” Friedman said.

As the smoke lingered, hundreds of questions poured in to the Washington Smoke Information blog, where Dhammapala and fellow smoke forecaster Farren Herron-Thorpe tried to provide updated forecasts, explanations, and advice. More than 2.5 million people visited the smoke blog over the week, while another 2.6 million looked to Ecology’s air quality monitoring map for the latest conditions.

Light winds in the middle of the week momentarily cleared the smoke from a few spots on the coast, but then also brought a second wave of smoke from Oregon fires. 

When would it end?

Hope on the horizon

After the dashed hope of relief on Sept. 13, commenters on the smoke blog and social media were skeptical of forecasts. To Dhammapala, Herron-Thorpe and other forecasters around the state, however, the signs for optimism were clear: Another weather system was due to arrive on the Washington coast Thursday, Sept. 17. The front would bring rain and gradually push the smoke northeast.

This time, the front arrived right on schedule. Air quality monitoring stations on the Washington coast showed good air quality by late morning Thursday. Further inland, though, air quality remained in the very unhealthy category in the Puget Sound region, and hazardous in most of Eastern Washington.

Slowly, slowly, that began to change. Friday afternoon saw heavier rains and scattered thundershowers. All over western Washington, people’s moods seemed to lighten as the smoke lifted, even though it hovered around the unhealthy range much of the day.

By Saturday, western Washington was clear – air quality monitors showed nearly all green on the map. Eastern Washington and Spokane had to wait another day for relief as the storm swept the smoke away.

And, on Sept. 21, it was all just a memory.

The new normal?

Are smoke events like this the “new normal”? Do we need to prepare for weeks stuck inside every summer from now on? Is there anything we can do to prevent that?

The Magic 8-ball tells us that the future is uncertain. Climate researchers predict that the number of acres burned each year in the west will continue to rise, as warmer winters eat away at mountain snowpack, and hotter summers dry foliage more quickly, setting the stage for wildfire.

Those long-term trends don’t tell us about any particular fire season, though – after major smoke events in 2017 and 2018, 2019 was a very mild year. And the wildfire season of 2020 was unexceptional for most of the summer. Until our luck ran out.

Even when fires race across the west, that doesn’t mean the more heavily populated regions will be hit by smoke. The sequence of events chronicled above shows that several factors have to come together in the right sequence for smoke events of this magnitude. In 2020, strong east winds allowed a super-massive plume of smoke to accumulate offshore, but had the wind shift been followed by stronger on-shore flows, that reservoir would have quickly drained.

Still, three of the past four years have seen days or weeks of unhealthy air in Seattle, Tacoma and Vancouver. Clearly, everyone in Washington needs to be prepared to protect themselves and their families when smoke arrives.

N95 masks – the most effective portable protection against PM2.5 – were hard to come by in this pandemic year. The simple cloth masks most Washingtonians wear to reduce the spread of the coronavirus provide little protection against the tiny particles.

Staying inside with the doors and windows closed is the best advice to reduce smoke exposure, but that’s a tall order when hazardous air quality goes on day after day. Making sure your air conditioner – for those fortunate enough to have it – or furnace is set to recirculate helps to keep smoke outside. A clean filter with a MERV rating above 11 will capture some of the particles that do get in, and can significantly improve indoor air quality as the air recirculates.

Tens of thousands of people watched Ecology’s “how-to” video showing a simple trick to strap a furnace filter to a box fan, offering an inexpensive way to create a clean air shelter.

2020 was a record-setter. Whether it is a harbinger of the future or an exceptional event remains to be seen. What 2020 has taught us, though, should be a call to action for everyone in Washington to be prepared for smoky skies and toxic air.


  1. Much thanks from Yakima for your guys’ hard work!!! =)

  2. 2020 has pretty much sucked all the way around. Thank you so much for keeping us informed; it was a very helpful lifeline, especially while sheltering from the smoke, to know that it would eventually be over.

  3. Just voicing my appreciation for all the hard detailed work that everyone involved with the "Smoke Blog" have done the past three weeks! This site was the first thing I looked at each morning and then referred to throughout each looong day sheltering inside. I so enjoyed the posts,learning along the way and constantly referring folks to this site. So glad I found you. You are appreciated and will be my 'go to' for info on the air.
    From one West Seattle resident Thank You, Thank You, job well done��

  4. Thanks for all your work and for keeping this blog updated. Seems like now would be a good time to order replacement filters and extra masks, to be prepared for future smoke events.

  5. What a comfort it has been to have insightful, compassionate, humorous information updated regularly. You guys have been the bright spot of hope during those loooonnnnggg smoky days...thank you!

  6. Echoing others' sentiments. Thank you for all your hard work keeping us informed throughout the emergency!

  7. Great article, Thank you so much for keeping us informed

  8. Same here. Even when the pollution news was pretty much "today will be the same as yesterday," this blog provided a welcome connection and source of information.

  9. Ditto to all the thankful comments above! Your information and tone were reassuring and sanity saving. Thank you! Marianne

  10. Echoing the comments of others. Simply wanted to say thank you so much for all the work and effort the team puts into keeping us informed and in the know. Thank you too for educating us in the process. Very vital work!

  11. Any idea whether the smoke from California fires will drift up this way this week? Thanks

    1. Hi Reed, we're watching it closely. Will blog about it if the threat exists

    2. Hi Ranil, thanks for your reply. I'll keep checking this blog for any updates, and in the meantime, will enjoy this clean air. Can't take it for granted.

  12. What a well written piece. Good work Andrew.

  13. Great post. Interesting you shied away from mentioning human-made climate change due to CO2 and other emissions. Why is that? Even NASA is very clear on this topic.

    1. Hi Shanefiddle,
      Climate change is an important, chronic, long-term problem that needs addressing and although tangentially tied to air quality in a broader sense (i.e probability of wildfires increasing in frequency and intensity), it's generally considered a separate issue from air quality as it pertains to health impacts. This smoke blog is intended to keep the public informed and updated about immediate and episodic smoke events and air quality issues that could directly impact health in the near term.


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