A supercell is the most organised and dangerous type of thunderstorm, characterised by a persistent, deep rotating updraft called a mesocyclone. Unlike ordinary thunderstorms that last 30–60 minutes, supercells can persist for 2–6 hours because their structure separates the updraft from the downdraft, preventing self-destruction. They are responsible for nearly all significant tornadoes, giant hail (>5 cm), and extreme wind events.
Supercells require strong environmental wind shear (wind changing speed and direction with height) and instability (high CAPE — Convective Available Potential Energy). The wind shear tilts the updraft, and the interaction between the storm's rotation and the wind field creates a distinctive structure visible on radar: a hook echo (indicating the mesocyclone area), a bounded weak echo region (the updraft vault), and sometimes a three-body scatter spike (indicating large hail).
Three subtypes exist: classic supercells (the textbook storm with distinct updraft, downdraft, and precipitation areas), HP (high-precipitation) supercells (wrapped in rain, making tornadoes difficult to see — particularly dangerous), and LP (low-precipitation) supercells (visually stunning with little rain but capable of producing large hail and tornadoes). In Spain, supercells occur most frequently in the Ebro valley, Catalonia, the Balearic Islands, and Andalusia during spring and autumn, when Atlantic troughs provide the necessary wind shear over the warm Mediterranean air.