A thunderstorm (or electrical storm) is a convective weather event characterised by lightning and thunder, produced by cumulonimbus clouds. Thunderstorms occur when the atmosphere is sufficiently unstable (warm, moist air at low levels with cooler air aloft) and a trigger mechanism (surface heating, fronts, orography, convergence) initiates deep convection. An estimated 1,800 thunderstorms are occurring globally at any given moment, producing ~100 lightning flashes per second.
The lifecycle of an ordinary thunderstorm comprises three stages: the cumulus stage (dominated by updrafts, cloud grows rapidly), the mature stage (both updraft and downdraft coexist — this is when lightning, heavy rain, hail, and strong gusts occur), and the dissipating stage (downdraft spreads out, cutting off the updraft's warm-air supply). Ordinary cells last 30–60 minutes, but multi-cell clusters, squall lines, and supercells can persist for hours through self-propagation mechanisms.
Thunderstorm hazards include lightning (causing deaths, fires, and power outages), heavy rainfall (flash floods), hail (crop and property damage), strong wind gusts and microbursts (wind damage and aviation hazards), and tornadoes (from supercells). In Spain, thunderstorms are most frequent in spring and autumn in the interior and Mediterranean regions, and in summer in mountain areas (Pyrenees, Sistema Ibérico). DANA events produce the most extreme thunderstorm activity, with Mediterranean storms generating exceptional rainfall rates exceeding 100 mm/hour. The radar network and lightning detection systems are the primary tools for monitoring and warning of thunderstorm hazards.