Investigation of large tornado outbreaks in the United States
Spector, David Anthony
MetadataShow full item record
Large tornado outbreaks are often responsible for the most destructive tornadoes in the United States. It is these outbreaks of twenty or more tornadoes that were responsible for over 60 percent of tornado-related deaths in the U.S. from 1984 through 1991, even though less than one-fourth of all tornadoes were included in large outbreaks over this same time period. An investigation of large tornado outbreaks in the United States from 1984 through 1991 was conducted, and several synoptic conditions were evaluated. Three of these conditions, the 250 mb jet stream maximum, the effects of upper difluence at 500 mb and the effects of a 500 mb cutoff low to the west or northwest of the outbreak, were checked for each of the 42 large outbreaks that were studied. It was found that all three conditions had a positive effect on both the size and intensity of a large tornado outbreak. However, when combinations of these effects were considered, it was found that the 250 mb jet stream maximum actually had a negative effect on the intensity of a large outbreak when a 500 mb cutoff low was present to the west or northwest of the target area.