What is a heat lightning?

Heat lighting is the flashes of light produced by distant electrical storms.  The flashes of lightning occur too far away for thunder to be heard.

Sometimes, on warm summer evenings, we see so-called “heat lightning”—silent flashes of light in the distant sky.  Heat lightning is really light from a flash of chain lightning that takes place beyond the horizon.  Chain, or forked, lightning is the lightning you see zig-zagging across the sky in any thunderstorm.

We just don’t hear heat lightning’s thunder because we are too far away.  We don’t see the lightning either.  We see its light reflected from high clouds.  Lightning is a big electric spark that spears its way across the sky.  During a thunderstorm, electrical charges are built up in the clouds.  If the charges become great enough, a flash of lightning occurs.

As the lightning flashes across the sky, it quickly heats the air in its path.  The heated air expands (spreads out) rapidly and sets a great sound wave in motion which we hear a few moments later as thunder.