Schematic of a serial derecho-producing convective system, showing location of associated bow echoes (arced portions of dashed / double-dotted line) relative to the cold front along which the parent thunderstorms typically form. Line-echo wave patterns, or LEWPs, mark the inflection points between individual bows. (After Johns and Hirt 1987).

"Ping-pong" animation showing the development and evolution of a typical serial derecho-producing convective system over the lower Ohio and Tennessee Valleys as viewed by radar (composite reflectivity data; April 19-20, 2011). The squall line evolves from discrete supercell storms that form over Illinois, Missouri, and Arkansas during the late afternoon (beginning of loop). The convective system ultimately grows to extend from Michigan to Mississippi, and produces four, large-scale bow echoes. For a period of time, three of the bows are connected in a wave-like pattern. The crest of each "wave" (i.e., the point of connection between an adjacent pair of bows) is known as a line-echo wave pattern, or LEWP. The duration of the animation is twelve hours. Selected surface observations are shown using conventional station plot format.