The calls came in, the Facebook messages filled the inbox and residents in Roanoke, Botetourt, Bedford and Alleghany counties (perhaps more), were left puzzled as to what caused a thunderous boom around 4:30pm, on an ordinarily sunny afternoon.
Before the scope of the sound was realized, it was thought some controlled explosions at a construction site caused the noise. That would have been around 2:30pm in north Roanoke county, not matching the other accounts.
Then, we started getting reports that local quarries may have been blasting at the time. I lived near one growing up, and those are typically also more localized, and it would have been rare to hear that widespread, even on an overcast day where sound echoes in the clouds.
"It sounded like thunder sounds," said one viewer. "A crack and then a rumble that lasted for a few seconds."
This statement was one of several that led me to abandon the idea of a ground source, and look to the sky.
No lightning was detected in the area Wednesday, so I only have two other theories. Again, not proven, but possible.
1) SONIC BOOM FROM A MILITARY JET
Sonic booms occur frequently with military jets. We typically just don't hear them because they are so far up and aren't allowed by civil aircraft over land. Interestingly, you may not know there's an offshore "Atlantic Test Range," a restricted airspace used for aircraft testing and training missions located in the Chesapeake Bay area off the coast of Maryland, Delaware, and Virginia.
Supersonic test flights take place there often, but are rarely heard here. Could Wednesday have been the exception?
The width of the boom beneath the aircraft is about one mile for each 1,000 feet of altitude. An aircraft, for example, flying supersonic at 50,000 feet can produce a sonic boom cone about 50 miles wide.
Ironically, the FAA released a Fact Sheet on supersonic flight timestamped February 27, 2019. I reached out with a phone call to see if there was any reason yesterday was a significant day for releasing this. I am waiting on a return call.
LINK TO FACT SHEET: https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=22754
2) DAYTIME FIREBALL ENTERING THE ATMOSPHERE
The other possible theory is a fireball entering the earth's atmosphere around that time. Because it was daylight and because sound travels slower, the object would have disappeared from sight before you even heard the boom. So even if you heard it and ran outside, the object would have been below the mountains and horizon.
According to the American Meteor Society, if a very bright fireball, usually greater than magnitude -8, penetrates the stratosphere, below an altitude of about 30 miles, and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below.
There were no fireball reports at that precise time on the American Meteor Society "Fireball Log" site. That doesn't mean it didn't happen, just that one wasn't spotted.
We may never know the source, but in researching the cause you, learn a little more about what's happening around you every single day.
If I find out anything else, I'll update this story. If YOU know more, pass it along, I'd love to hear your theory.
-Chief Meteorologist Brent Watts