What Is a Supercell Thunderstorm?

Supercells are the most powerful type of thunderstorm and are responsible for nearly all significant tornadoes. What distinguishes them from ordinary storms is a mesocyclone — a rotating updraft that can span 5–10 km in diameter. This rotation develops when wind shear (winds changing speed or direction with altitude) tilts horizontal spin into the vertical. Supercells can last for hours, produce giant hail (over 5 cm), destructive winds, torrential rain, and intense lightning. They are most common in the central United States (Tornado Alley) but occur worldwide. Doppler radar detects the mesocyclone rotation, providing critical warning time before tornado formation.