A particularly large and vigorous mesoscale convective system, defined from the properties of the cloud shield as revealed by satellite infrared imagery. The area with a temperature below −52 °C must exceed 50 000 km2, and there must be a continuous area, exceeding 100 000 km2, below −32 °C. This larger area must be elongated, with an eccentricity (ratio of minor axis to major axis) of 0.7 or more. These criteria must be satisfied for a period of more than 6 hours for the classification to apply.
Subjects: Meteorology and Climatology.