On the climatological distribution of tornadoes within quasi-linear convective systems

Tornadoes threaten our communities every year. They can occur throughout the U.S. in any season, and at any time of day. Currently unknown and an area of concern is the type of storms from which tornadoes form. "Supercell" thunderstorms are thought to be the most common tornado producers. Yet, recent studies have brought forth the question of how many tornadoes form within other storm types, such as squall lines or hurricane rainbands. A related question regards possible relationships between parent storm type and tornado intensity. In this study, Doppler radar reflectivity images were analyzed for each tornado case between March 1998 and February 1999 to determine whether the parent storm type was a quasi-linear convective system (QLCS), cell, or hurricane rainband. We will present the frequency of the tornadoes by the parent storm type for the 12-month period. In addition, seasonal, diurnal, and geographical distributions will be presented to show any patterns in frequency on such scales. A distribution by damage intensity will also be presented to illustrate the level of danger each classification of tornadoes can pose. Results based on an analysis of six months of data suggest that of all U.S. tornadoes that were reported, 60%, 25%, and 15% are spawned by cells, QLCSs, and hurricane rainbands, respectively.