What caused that crazy loud thunder this morning, anyway?


Loud thunder resembling a long, rolling explosion hit Philadelphia this morning at 10:20 a.m., rattling buildings and sending dogs everywhere scattering into closets. It surprised basically everyone — but what made it happen?

“Sound waves are better able to travel in cold, dense air,” noted NBC meteorologist Bill Henley in a report this morning. “Sound does travel better in denser air, and that’s what we had this morning. So, it’ll make thunder and lightning sound so much stronger.” That dense air, according to reports, came from the cold air moving out and warm moving in.

“Thunder is the sound made by lightning’s effects on the air column it goes through,” noted Dr. Greg Forbes, severe weather expert for the Weather Channel, in 2011.The heated air column expands explosively and creates a sound wave… What makes thunder louder on some occasions than others? Most of the time it has to do with how the temperature changes with height. The short answer is that thunder tends to be loudest when there is a cold pocket near the surface and warm air above it— an ‘inversion.’”

Essentially, most thunderstorms form amid warm, unstable conditions. When it’s cold—as it has been recently—and getting warmer, the air becomes extremely dense, which makes that explosion of sound stronger.

According to reports, this morning’s storm has broken windows and downed power lines in the region, even knocking out power in Roxborough. That dense air is expected to stay with us over the early afternoon hours, though it will get less dense as the temperatures rise. And more profound warming is on the way: The forecast for Friday and Saturday says we’ll get up into the 50s.

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