2002 Annual

Monday, 14 January 2002
The Relationship Of Large-Scale Surface Boundaries To Convective Initiation And Strong And Violent Tornado Occurrence
David M. Bolen, Univ. of Northern Colorado, Greeley, CO
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 these boundary types, while outbreak events (> 10 tornadoes) varied widely been episodes. This was especially true when comparing the outbreak of 26 April with other outbreaks of the period.

Boundaries also served as favored spots for convective initiation. However, convection did not necessarily stay on the boundary or boundaries in which it initiated until the tornado(es) occurred. In fact, in 70% of the cases the convection moved off of the initiation boundary, and the tornado(es) occurred either on different boundaries or in a different sector. In the majority of these cases, the tornado(es) occurred on large-scale outflow boundaries that were generated by the convection or convective cluster. Some implications of future work are also discussed.

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