‘Boom!’ Sonomans look to the skies for an answer following nocturnal noises

People all over Sonoma County looked up at about 7:40 p.m. on Thursday, Nov. 21, when a brief series of “booms” rolled across the valleys. But there was no glow in the sky, no jet, and the stars were visible so there were no clouds. Was it thunder?

Or was it a meteor?

It may be no coincidence that the sound corresponded to a large but infrequent meteor shower, known as the Unicorn (or Monocerotids, from the constellation of its visible origin), seen only every 25 years or so – and last reported in 1995. But meteors are usually silent apparitions, fleeting and ghostly.

In social media groups, many people dialoged about the Thursday night noises. Descriptions of the noises ranged from “rumbles like thunder” to “like a limb fell on the house.”

And it didn’t seem to be particularly localized, but strong throughout the Sonoma Valley, reported in Nextdoor neighborhoods from Temelec to Denmark Street. Similar social media networks reported the noises at about the same time in Healdsburg, while others on Facebook said it was heard in Sebastopol, Santa Rosa, Cloverdale, Petaluma, Napa and Marin.

More than once on Facebook, a Patch article titled “Meteor the Size of a Car Hits Bay Area” was posted as an answer, despite its Oct. 18, 2012 date. It describes a large meteor that was “seen and heard throughout the Bay Area,” complete with a photograph of the fireball.

But this time there were there no lights signaling the source of the noise. The Berkeley Seismology Lab’s earthquake map showed no detectable shaking at that time, even in the often-jittery Geyser Peak area.

Deanna Contreras of PG&E said succinctly, “If nobody lost power then it wasn’t a transformer.” She noted that customers who had been affected by the PSPS had power back by 5 p.m.

Local law enforcement said they heard about the noises, but there were no official reports about them. “Typically when we hear about loud booms, we think about the ag community around the vineyards, but harvest is pretty much over by now,” said Sgt. Michael Baraz of the Sonoma Police Department.

“I do not know of any loud booming noises coming from vineyards this time of year. Not sure what it would be,” said Steve Sangiacomo of Sonoma’s Sangiacomo Family Vineyards, a large area wine-grape farmer.

“We had a few calls regarding loud booms,” said Sgt. Juan Valencia of the Sonoma County Sheriff, saying the calls arrived around 8 p.m. Two Sheriff’s reports at 19:50 and 19:51 – around 7:50 pm. – were reported as “promiscuous shooting,” a catch-all that also includes fireworks. “The rumor on social media was meteor storm,” said Valencia.

“It’s possible, but unlikely. I haven’t seen any reports of a fireball from the shower,” said Greg Reynolds of the Robert Ferguson Observatory about a meteor-sonic boom connection. “All reports indicate a mediocre (meteor) show.”

Indeed, the highly-anticipated and widely-touted Unicorn meteor shower turned out to be something of a bust, according to EarthSky.org, despite predictions of up to 400 meteors per hour.

“It was a dud; It seems unlikely that it had anything to do with the noise that you heard,” said Colleen Ferguson, whose father helped create the observatory at Sugarloaf Ridge.

Both Reynolds and Sonoma Valley High School science teacher Dean Knight said the meteor shower produced few observable meteors on Thursday night, despite a meteor-shower watch at the observatory.

While a sonic boom caused a meteor is unlikely, it’s not impossible. Perhaps the meteor had already fallen, and its fleeting appearance had gone unnoticed – then the sound arrived many seconds, even minutes later.

“Meteors are able to create sound waves,” writes Alastair Gunn, a radio astronomer at the University of Manchester, on the Science Focus website. “As they tear their way through the atmosphere they can create a sonic boom in the same way a fast-moving aeroplane does.”

If it were a meteor, it’s possible the sound many not reach the surface “until many minutes after the meteor appeared,” Gunn wrote, and given the fleeting nature of a high-altitude meteor it’s quite possible the two were not synchronous.

“Ground width of the boom exposure area is approximately one mile for each 1,000 feet of altitude; that is, an aircraft flying supersonic at 30,000 feet will create a lateral boom spread of about 30 miles,” according to the U.S. Air Force’s sonic boom fact sheet. That’s about the direct distance from Napa to Sebastopol, which both recorded the sounds.

“Depending on the aircraft’s altitude, sonic booms reach the ground two to 60 seconds after flyover,” the report continues. But not all booms are heard at ground level due to factors of temperature and altitude - the higher the source of the supersonic sound, the more likely it is to be refracted, or bounced upward, by the thick atmosphere closer to the surface.

Knight, a teacher at Sonoma Valley High and a RFO volunteer, agreed that meteors could create a sonic boom. “Meteors can do that, but it’s strange,” he said, citing a 2013 fireball in Russia that generated a high-pressure sonic boom. He also mentioned that most aircraft now break the sound barrier far from populated areas, so the general public doesn’t hear sonic booms as often.

“It could have been a rocket re-entry, you could get a sonic boom but not a flash,” he speculated. “It’s a mystery.”

By coincidence, a substantial fireball – though no sonic boom – was reported in northern Oregon at about sundown, at least an hour before the local booms.

As of press time, the US Air Force has not responed to both phone and email inquiries.

Email Christian at christian.kallen@sonomanews.com.