Abstract:
This preliminary study examines the occurrence of strong and violent tornadoes to determine the relationship between convective initiation, tornado occurrence, and boundary location. Tornadoes were gathered from events occurring during the warm (Jun.-Aug.) and cool (Jan.-Mar.) season portions of 1991, as well as a spring transition season major outbreak on 26 April. The majority of strong and violent tornado episodes occurred on or near preexisting surface boundaries. Isolated events (1-2 tornadoes) had the highest association with preexisting surface boundaries, while outbreak events (> 10 tornadoes) varied widely been episodes. This was especially true when comparing the outbreak of 26 April with the other outbreaks of the period.
Boundaries also served as favored spots for convective initiation, but the convection did not necessarily stay on the initiation boundaries until the tornado occurred. In fact, in 70% of the cases, the convection moved off of the boundary in which it initiated, and tornado(es) occurred on different boundaries or in different sectors. In the majority of these cases, the tornado(es) occurred on large-scale outflow boundaries generated by the convection or convective cluster. Some implications of future work are also discussed.
Paper available upon request.