Synopsis: A mesoscale convective system (MCS) is composed of precipitating convective clouds that interact to produce a nearly contiguous, extensive area of precipitation. Chapter 8describes MCS structure and organization, and then explains the dynamical links among structure, longevity, and intensity. The quasilinear MCSs, especially those that have leading edges that “bow” outward, can produce swaths of damaging “straight-line” surface winds. Proposed mechanisms for this wind production are described, including one that involves vertical vortices at low levels. The chapter also includes discussions of mesoscale convective complexes, another common organizational mode, as well as of the remnant vortices that these and other MCSs often generate.

Overview of MCS Characteristics and Morphology

A mesoscale convective system (MCS) is an organized collection of two or more cumulonimubus clouds that interact to form an extensive region of precipitation. As observed in weather radar scans at low elevation angles, the precipitation is nearly contiguous, especially at the leading edge of the system (Figure 8.1a). Indeed, this characteristic is one that allows for an observational distinction between an MCS and a group (or line) of discrete cells; it additionally has consequences on the MCS dynamics, as will be explained shortly. Another characteristic is the time scale, which typically is much longer than the ~1 h life cycle of the individual cumulonimbi comprising the system (see Chapter 6).