A climatology of tornado intensity assessments

Abstract

An increasing number of significant and violent tornado events in the United States have been documented and mapped at extremely high resolution by government, research and private entities using remotely sensed and post-event damage surveys; however, these assessments often generate inconsistent spatial measures of tornado strength, even for the same event. This investigation assembles a portfolio of contemporary tornado events that contain spatially comprehensive damage and/or wind velocity information from a diverse set of sources. Thereafter, the relationship between land-use/cover and tornado intensity is examined in order to quantify spatial measures of damage indicator bias in post-event tornado damage surveys. A climatology of both significant and violent tornado intensity assessments is then created, promoting the generation of synthetic, or model, paths with observationally constrained damage length and width metrics by the Enhanced Fujita scale magnitude. Results from the climatology and collection of synthetic paths are compared to previous observed, empirical and theoretical assessments, revealing differences in the spatial scale of the overall tornado footprint, as well as percentage contribution of swaths by Enhanced Fujita scale magnitude. The range of synthetic paths produced may be used to assess potential tornado damages to the population, the built environment and insurance portfolios.

A Monte Carlo model for estimating tornado impacts

“…The 10 000 year Oklahoma simulation generated mean significant tornado length and width of 17.1 km and 170.6 m, respectively (Table 1). Compared to the observed data, and as illustrated in Brooks (2004) and Strader et al (2015a), tornado length and width typically increase as EF magnitude escalates. Mean tornado lengths for significant tornadoes ranged from 12 km (EF2) to 63.9 km (EF5), while mean tornado widths varied from 122.4 m (EF2) to 551.5 m (EF5).…”

“…generated length multiplied by width). Obviously, this is not the most accurate depiction of actual tornado coverage as tornado intensity, width and azimuth vary greatly as it traverses a landscape (Strader et al , ). Daneshvaran and Morden () use a formula acquired from Twisdale et al () to determine how tornado wind speed and the inferred damage intensity fluctuate throughout its life cycle.…”

“…Daneshvaran and Morden (2007) use a formula acquired from Twisdale et al (1981) to determine how tornado wind speed and the inferred damage intensity fluctuate throughout its life cycle. Similarly, future TorMC model iterations will integrate tornado intensity distributions (TID) (Strader et al, 2015a) in conjunction with a weighted 'random walk' method (Weisstein, 2002b) to capture better how tornado intensity, width and azimuth change as the tornado navigates a setting. Future TorMC versions will be able to ingest vector cost surfaces, which will permit the implementation of the areal weighting tornado cost-extraction method.…”

“…Although there are many issues with the observed tornado data (e.g. width (Brooks, ; Strader et al , ); reporting bias (Brooks et al , ; Doswell et al , ; Anderson et al , ); counts (Brooks et al , ; Verbout et al , ; Tippett et al , )), these data are the only accessible source of extensive tornado event information. The SVRGIS tornado shapefile, which contains the observed tornado record, is integrated into the TorMC model.…”

“…Given the distribution of tornadic winds within a footprint, only a small percentage of the total HUs affected by the tornado footprints are subject to significant or violent tornado wind speeds (e.g. Strader et al , ).…”