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Relationships between Tornado Intensity and Various Wind and Thermodynamic Variables

John R. ColquhounBureau of Meteorology. Sydney, Australia

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Philip A. RileyBureau of Meteorology Research Centre, Melbourne, Australia

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Abstract

Statistical relationships between tornado intensity and various stability and wind-related parameters are determined from a dataset of more than 200 tornado proximity soundings. Soundings were obtained from two sources: the University of Missouri and from analyses. The surface to 600 hPa wind shear, streamwise vorticity, storm velocity, and storm-relative environmental helicity are shown to be best correlated with tornado intensity. A multiple regression analysis produced an equation relating tornado intensity to the lifted index and the surface to 600 hPa wind shear. This relationship could be used operationally to predict tornado intensity. Mean temperature, dewpoint temperature, and wind profiles are presented for each tornado intensity category and these may be useful as input to numerical thunderstorm simulations. Progressively cooler temperatures and increasing wind speed and vertical wind shear are evident with increasing tornado intensity. A modified form of the bulk Richardson number is derived to assist the forecasting of isolated supercell thunderstorm occurrence. The modified form uses parameters that are readily available to the operational forecaster.

Abstract

Statistical relationships between tornado intensity and various stability and wind-related parameters are determined from a dataset of more than 200 tornado proximity soundings. Soundings were obtained from two sources: the University of Missouri and from analyses. The surface to 600 hPa wind shear, streamwise vorticity, storm velocity, and storm-relative environmental helicity are shown to be best correlated with tornado intensity. A multiple regression analysis produced an equation relating tornado intensity to the lifted index and the surface to 600 hPa wind shear. This relationship could be used operationally to predict tornado intensity. Mean temperature, dewpoint temperature, and wind profiles are presented for each tornado intensity category and these may be useful as input to numerical thunderstorm simulations. Progressively cooler temperatures and increasing wind speed and vertical wind shear are evident with increasing tornado intensity. A modified form of the bulk Richardson number is derived to assist the forecasting of isolated supercell thunderstorm occurrence. The modified form uses parameters that are readily available to the operational forecaster.

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