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Rolling thunder caused by shock waves

I can understand why lightning makes a short, loud cracking noise, but why does it sometimes make a long, rumbling noise?

— Aaron, Medford

A lightning bolt can reach 54,000 degrees — five times hotter than the surface of the sun, according to the National Weather Service.

When the air around the bolt is heated to such temperatures in just a fraction of a second, a phenomenon known as "explosive expansion" occurs. The super-heated air expands so rapidly it compresses the air in front of it, triggering shock waves, NWS says.

The initial sound of lightning reaches the ear with a loud bang or crack, NWS says.

But as the shock waves continue to travel away from the strike, they become stretched and distorted, producing a more muted sound. When the shock waves reach a person who is far from the lightning strike, the listener will hear a continuous booming and rumbling sound, according to NWS.

— Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. We’re sorry, but the volume of questions received prevents us from answering all of them.