An ordinary thunderstorm lives about an hour and a half in three acts
Most thunderstorms are born, peak and die in roughly 90 minutes, each stage lasting around half an hour. Warm, moist air shoots upward, builds a cloud that can top 20 kilometres, then collapses under its own rain. Add the right wind shear, though, and a storm can separate its updraft from its downdraft and rage for hours.
Three ingredients make a thunderstorm: moisture, unstable air and something to lift it, such as a front, converging winds, sunlit ground or rising terrain. As moist air climbs it cools and its vapour condenses, releasing latent heat that keeps the parcel warmer and lighter than its surroundings, so it keeps rising. Forecasters gauge this potential with measures like convective available potential energy. Storms can form anywhere but are most frequent in the mid-latitudes, where tropical and polar air masses meet.
In the first, cumulus stage, towering clouds grow as updrafts carry moisture skyward. In the mature stage the rising air hits a cap, often the tropopause, and spreads sideways into the familiar anvil. Droplets merge and freeze; strong updrafts can hold ice aloft until it falls as hail rather than rain. Falling precipitation drags air down, and the coexistence of updraft and downdraft defines maturity, along with turbulence, lightning and sometimes tornadoes. Finally the downdraft wins, spreading cool air along the ground that cuts off the warm inflow, and the storm dissipates. The average storm spans about 24 kilometres.
Wind shear decides the type. Single-cell storms, the classic summer afternoon kind, form in calm conditions and last 20 to 30 minutes. Multicell clusters, the most common type, keep spawning new cells so the group can persist for hours. Squall lines stretch along or ahead of cold fronts. Supercells, the strongest, need shear typically above 25 knots in the lowest 6 kilometres, and they rotate like small cyclones, producing large hail, violent winds and tornadoes.
Damage comes mainly from downburst winds, hail and flash floods, and a sudden downburst can rob an aircraft of airspeed and lift. Dry thunderstorms, which yield lightning but little rain, can ignite wildfires. In the tropics, organised storm systems can seed hurricanes. Myths about thunder persisted as late as the 18th century, and thunderstorms have since been observed on Jupiter, Saturn and Neptune, and probably on Venus.
Source: Thunderstorm
