Portland Lit Enough Fireworks Last Night for the Smoke to Show Up on Weather Radar

But the fire bureau says the city ban is having an effect.

HOLIDAY SHOPPING: Black Jack Fireworks outside Vancouver, Wash. (Jarod Opperman)

Did that seem like a lot of fireworks last night for a city that has ostensibly banned them? The combination of Portland’s scofflaw pyrotechnics and its authorized displays produced enough smoke to trigger an atmospheric measurement that meteorologists say they “haven’t ever noticed before.”

Starting at 11:45 pm Monday, there was a two-hour period of “higher reflectivity” over downtown and North Portland, according to the local office of the National Weather Service. Reflectivity, measured in decibels, is the amount of electromagnetic pulse bounced back to a radar after hitting matter in the atmosphere.

Light rain is usually responsible for moving decibels of reflectivity into the range they reached last night. But there wasn’t any rain July 4. So the reflectivity levels struck NWS meteorologist John Bumgardner as notable.

“The lower the reflectivity, the less of the pulse that goes out is coming back to the radar, so most of the electromagnetic pulse that the radar emitted went through the smoke, but a small amount of it was bounced back to the radar,” Bumgardner tells WW.

The reflectivities over downtown and North Portland from 11:45 pm Monday to 2 am Tuesday were “generally in the 10- to 15-decibel range with a few slightly higher than that,” Bumgardner says. For reference, Bumgardner says that without precipitation, reflectivities are usually below 10 decibels due to background noise, leading him to conclude that a “5- to 8-decibel uptick in reflectivity occurred just after fireworks.”

“There was thick smoke from the fireworks last night, and so the receiver was picking up on some decibels of reflectivity on the very low end of the spectrum,” Bumgardner tells WW.

In addition to reflectivity, smoke from fireworks has the potential to affect air quality, particularly at night, Bumgardner says. During the day, warm air near the surface has an inclination to rise above colder levels. However, at night, air is colder near the surface with no inclination to rise, trapping any smoke contained in lower atmospheric layers.

“It can decrease air quality, and I think this actually happened this morning where we had lower air quality being reported,” Bumgardner tells WW. “The timing of the fireworks allows the smoke to get trapped and reduce air quality.”

As of 11:10 am on Tuesday, air quality in areas surrounding Salem and Portland was categorized as “moderate,” Bumgardner says. According to Oregon Department of Environmental Quality measurements, air quality last night deteriorated to the categorization of “unhealthy” in Woodburn and “unhealthy for sensitive groups” in Beaverton, Tualatin and Gresham.

Public displays of fireworks authorized by permits occurred last night at Oaks Amusement Park and the Waterfront Blues Festival. But anecdotal evidence across the city suggests much of the smoke came from fireworks that were banned citywide.

In March, the Portland City Council unanimously voted to ban the sale and use of fireworks in Portland, citing concerns about wildfires and fire-related injury.

Despite a ban on the sale and use of fireworks announced last summer by Mayor Ted Wheeler, a July 4 apartment fire caused by discarded fireworks killed three people, drawing attention to fires caused by illegal fireworks.

Calls to the fire bureau about accidents caused by fireworks have decreased since the passage of fireworks bans, fire bureau public information officer Terry Foster tells WW. “In the 2020 season, about 20% of the fire calls were reported to be fireworks related. Last year, there was only 5%,” Foster says.

Yesterday, the fire bureau received nine calls related to fireworks, including two structural and three vehicle fires, although investigations may uncover other fires generated by fireworks, Foster says.

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