Tuesday, 5 October 2004
The focus of this research is to show a historical representation of several smaller apparent tornado alleys across the United States as determined by a F3 - F5 tornado climatology study. Owing to the rapid increase of weak tornadoes reported in the last 20 years, it is inarguable that the most consistent records in both the current and historic tornado databases are at the higher end of both the F-scale rating and damage path length spectrums. We used the program Severe Plot (John Hart, SPC), to obtain tornado data from 1950 to 2003. For tornado records between 1880 and 1950, the reference book Significant Tornadoes 1680-1991 by Thomas Grazulis was the sole source of information. From these databases, we have constructed a tornado climatology map showing all reported F3 to F5 tornadoes with path lengths equal to or greater than 25 miles from 1880 to 2003. Additional maps were constructed with either no path length discrimination or smaller timescales than the full period of record to determine if any biases existed with the primary climatology map. Based on these maps, many regional "alleys" for long path F3 - F5 tornadoes are identified in the full period of record. Although, there may undoubtedly be specific meteorological reasons for why these apparent alleys exist, one hypothesis is they are related to topographic features that may modulate environmental conditions in ways that favor development of these types of tornadoes. This paper does not seek to present infallible proof for this relationship, however, it appears that variability does exist in the term "tornado alley".
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