Dear Tom,
What causes heat lightning?
–Mike Murphy,Chicago
Dear Mike,
Heat lightning is nothing more than ordinary lightning produced by a thunderstorm too far away for the thunder to be heard. With summer thunderstorms routinely building to heights in excess of 50,000 feet, lightning from these storms can be visible at distances beyond 125 miles. In contrast, the sound of thunder can rarely be heard beyond about 15 miles. In fact, the parent thunderstorm cloud producing the lightning may actually be below the horizon, but due to the curvature of the Earth’s surface, flashes emanating from the upper levels of the cloud are visible. The term heat lightning came into use because people spent time outdoors on hot, humid summer evenings and were able to view the distant lightning.
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Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or: asktomwhy@wgntv.com
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