A
mesoscale convective system (
MCS) is a complex of
thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than
extratropical cyclones, and normally persists for several hours or more. A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as
tropical cyclones,
squall lines,
lake-effect snow events,
polar lows, and
Mesoscale Convective Complexes (MCCs), and generally form near
weather fronts. The type that forms during the warm season over land has been noted across
North America,
Europe, and
Asia, with a maximum in activity noted during the late afternoon and evening hours.