Definition

Mesoscale Convective System (MCS) - A region where several thunderstorms have merged to create a continuous area of convective instability where cloud with a horizontal extent greater than 100 km (54 nm) exists. Such systems normally continue to exist for several hours. They can occur in both tropical and temperate latitudes.

Description

Within a MCS is a cluster of multi-celled thunderstorms called Mesoscale Convective Complex (MCC). Such a complex would normally be expected to reach its peak intensity at night having formed during the afternoon and evening. They can reform the next night as well, by way of the same processes of the initial formation. As a guideline, the United States National Weather Service defines a MCC as having an area of cloud top of at least 100,000km² at a temperature of -32° C or less or an area of cloud top of at least 50,000km² at a temperature of -52° C or less. In both cases, they generally have a ratio of minor to major axes of at least 0.7.