ON THE EPISODIC NATURE OF DERECHO-PRODUCING CONVECTIVE SYSTEMS IN THE UNITED STATES

Convectively generated windstorms occur over broad temporal and spatial scales; however, one of the larger-scale and most intense of these windstorms has been given the name ‘derecho’. This study illustrates the tendency for derecho-producing mesoscale convective systems to group together across the United States – forming a derecho series. The derecho series is recognized as any succession of derechos that develop within a similar synoptic environment with no more than 72 h separating individual events. A derecho dataset for the period 1994–2003 was assembled to investigate the groupings of these extremely damaging convective wind events. Results indicate that over 62 % of the derechos in the dataset were members of a derecho series. On average, nearly six series affected the United States annually. Most derecho series consisted of two or three events; though, 14 series during the period of record contained four or more events. Two separate series involved nine derechos within a period of nine days. Analyses reveal that derecho serie