Supercell tornadoes are much stronger and wider than damage-based ratings indicate

Jeff Duda

EF6+, PhD
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Oct 7, 2008
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Came across a press release on this recently published paper today.

Apparently our friends at CSWR collected enough data with DOWs on tornadoes since the late 90s to determine that NWS official ratings for tornado intensities and widths were statistically significantly underestimated compared to DOW measurements. Some of the figures within (namely, Fig. 3) are pretty telling of the discrepancy between NWS estimated and DOW measured ratings.

Also substantial is that they found essentially zero correlation between tornado width and maximum ground-relative wind speed; that said - wider tornadoes are not statistically stronger!

paper link (I think it's free): Supercell tornadoes are much stronger and wider than damage-based ratings indicate

Abstract said:
Tornadoes cause damage, injury, and death when intense winds impact structures. Quantifying the strength and extent of such winds is critical to characterizing tornado hazards. Ratings of intensity and size are based nearly entirely on postevent damage surveys [R. Edwards et al., Bull. Am. Meteorol. Soc. 94, 641–653 (2013)]. It has long been suspected that these suffer low bias [C. A. Doswell, D. W. Burgess, Mon. Weather Rev. 116, 495–501 (1988)]. Here, using mapping of low-level tornado winds in 120 tornadoes, we prove that supercell tornadoes are typically much stronger and wider than damage surveys indicate. Our results permit an accurate assessment of the distribution of tornado intensities and sizes and tornado wind hazards, based on actual wind-speed observations, and meaningful comparisons of the distribution of tornado intensities and sizes with theoretical predictions. We analyze data from Doppler On Wheels (DOW) radar measurements of 120 tornadoes at the time of peak measured intensity. In striking contrast to conventional damage-based climatologies, median tornado peak wind speeds are ∼60 m⋅s−1, capable of causing significant, Enhanced Fujita Scale (EF)-2 to -3, damage, and 20% are capable of the most intense EF-4/EF-5 damage. National Weather Service (NWS) EF/wind speed ratings are 1.2 to 1.5 categories (∼20 m⋅s−1) lower than DOW observations for tornadoes documented by both the NWS and DOWs. Median tornado diameter is 250 to 500 m, with 10 to 15% >1 km. Wind engineering tornado-hazard-model predictions and building wind resistance standards may require upward adjustment due to the increased wind-damage risk documented here.
 
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