A study reports observations of tornado wind speed and size that show stronger and wider tornadoes than previous damage-based estimates indicated. Ratings of tornado intensity and estimates of wind speed come from reports of tornado damage, which are biased partly due to the rural locations of most tornadoes and their minimal damage to well-engineered structures. Thus, the true distribution of tornado wind speeds and sizes is unclear. Joshua Wurman and colleagues analyzed wind speed measurement data from 120 tornadoes, collected by Doppler on Wheels mobile Doppler radar instruments. These direct measurements of tornado characteristics suggest that the median peak wind speeds are around 60 m/s, which is sufficient to merit Enhanced Fujita scale (EF) scores of 2 to 3. Comparison to National Weather Service ratings showed that the previous EF/wind speed estimates are 1.2 to 1.5 categories lower than those observed by Doppler on Wheels instruments. The authors further found that around 20% of tornadoes are capable of the most destructive EF scores of 4-5. The authors found that the median tornado diameter is around 250-500 m, which is wider than that indicated by damage-based surveys alone. According to the authors, the results suggest that tornado risk assessments, as well as building wind resistance standards, may need to be upgraded to reflect the observed strength and size of tornadoes.
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Article #20-21535: "Supercell Tornadoes are Much Stronger and Wider than Damage-Based Ratings Indicate," by Joshua Wurman, Karen Kosiba, Trevor White, and Paul Robinson.
MEDIA CONTACT: Joshua Wurman, University of Illinois Urbana-Champaign, IL; tel: 303-330-4444; email: < jwurman@illinois.edu >
Proceedings of the National Academy of Sciences