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Ask the Meteorologist: Thunder

ASK THE METEOROLOGIST

“What Causes Thunder?”

Kanai Liufau, Medford Montessori

lightningIn the spring, the last bit of winter air moves in above the warmer air at the surface. Because of this phenomenon, thunderstorms become more numerous. As the name suggests, thunder is a key factor in these storms. But what causes this phenomenon?

Thunder is simply the effect of a lightning strike. When lightning occurs, the air immediately surrounding the bolt is superheated to up to 50,000 degrees Fahrenheit. That’s three times hotter than the surface of the sun! A combination of the expansion and contraction of the air molecules is what causes the sound of thunder.

vibrations The initial heating and expansion of the air causes the “crack” that is first heard in thunder. The air quickly contracts back to its original size and then like a rubber band, continues vibrating slower and slower. This vibration is what causes the rumble that is heard after the initial crack. The vibration happens until the air molecules become stagnant again.

Lightning can sometimes be seen without hearing thunder. This is sometimes referred to as “heat lightning.” Some people think that heat causes lightning with no sound. This is a common misconception.  It is important to remember that ALL lightning creates thunder. If you see lightning, but don’t hear any thunder after, what’s actually happening is the bolt is too far away from you for the sound to travel. Sound waves and vibration can only travel so far through the air. So sometimes you will see lightning and not hear the thunder.

Meteorologist Seth Phillips