For the aircraft with similar names, see P-47 Thunderbolt and A-10 Thunderbolt II. Thunder is the sound generated during and after an electrical discharge in the atmosphere (lightning). It ranges from a sharp, crack-like snap to a long, rolling rumble. The character of thunder depends on the type of lightning, the distance between the strike and the listener, and the surrounding terrain and atmospheric conditions.

How thunder forms

Thunder originates when a lightning channel suddenly heats the air along its path to very high temperatures. That rapid heating causes the air to expand explosively and produce a pressure disturbance that propagates outward as a sound wave. Close to the flash the disturbance is a strong shock; at greater distances it arrives as audible sound. Scientists describe this process as a thermoacoustic or shock-wave phenomenon tied directly to the energy release of a lightning stroke. See also general information about lightning here and about the energy involved here.

Audible qualities and types

Thunder can present in several forms. A single, sharp clap often follows cloud-to-ground strikes that produce short, concentrated channels; a long, rolling rumble results when multiple branches of a lightning channel or successive strokes occur over a range of distances, producing overlapping sound waves. Reflections from buildings, hills, and layers in the atmosphere also stretch and modulate the sound, giving thunder its characteristic echoing, variable tone. The sound is sometimes described with onomatopoeic words like "boom" or "crash" — informal descriptions that reflect human perception of loudness and timbre (boom).

Estimating distance and practical rules

Light from a lightning flash reaches the eye almost instantly, while sound travels much slower through air. Because of this difference, people commonly estimate how far away a lightning strike is by counting the seconds between the flash and the thunder and converting that interval into distance. A rough guideline is to divide the number of seconds by three to get the distance in kilometres, or to divide by five for the distance in miles. This simple method of timing the delay is widely used for situational awareness (timing).

Safety and practical importance

Hearing thunder means lightning is close enough to be dangerous. Basic safety advice includes seeking shelter indoors or inside a hard-topped vehicle when thunder is audible. The informal "30-30" safety guideline recommends seeking cover if the time between a lightning flash and the thunder is 30 seconds or less, and waiting 30 minutes after the last heard thunder before resuming outdoor activities. Thunder serves as a practical, immediate warning that a storm is producing electrical activity. It is often associated with heavy rain and gusty winds in convective storms (rain) and (storm).

History, culture, and notable facts

  • Across cultures, thunder has been linked to gods, omens, and natural power; ancient myths frequently personified thunder and lightning.
  • Thunder differs from similar loud atmospheric sounds such as a sonic boom: sonic booms are produced by objects moving faster than sound, while thunder results from thermal expansion along an electrical discharge.
  • Observers sometimes report hearing thunder at surprisingly long ranges under certain atmospheric conditions, because sound can travel farther when it refracts or ducts between layers of air.

Measurement and scientific study of thunder overlap with the study of lightning and atmospheric electricity. Researchers use combined optical, acoustic, and electromagnetic observations to link the sound of thunder with specific lightning channels and to better understand the energy and dynamics of storms. For background readings and reference material, see related resources about sound descriptions and general overviews on nomenclature. Additional meteorological context can be found through introductory materials on storm energetics and practical safety summaries on timing methods.