An Objective Basis for Forecasting Tornado Intensity

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  • 1 NOAA, Environmental Research Laboratories, Weather Research Program, Boulder, Colorado
  • | 2 Bureau of Meteorology, Hobart, Australia
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Abstract

Although violent tornadoes comprise only 2.3% of tornado occurrences in the United States, they cause 68% of the fatalities attributed to tornadoes and severe thunderstorms. Despite these statistics, no attempt is made to forecast or warn of tornado intensity. A basis for this is provided in a study of more than 200 tornado events. Tornado intensity is best related to the magnitude of the vertical wind shear in the layer between the ground and 600 hPa. The results for this and other shear parameters are statistically highly significant when the data are grouped into two or three intensity classifications. Stability, as indicated by the “lifted index,” and midtropospheric relative humidity, correlate poorly with tornado intensity. The relationships established have application to tornado forecasting and nowcasting.

Abstract

Although violent tornadoes comprise only 2.3% of tornado occurrences in the United States, they cause 68% of the fatalities attributed to tornadoes and severe thunderstorms. Despite these statistics, no attempt is made to forecast or warn of tornado intensity. A basis for this is provided in a study of more than 200 tornado events. Tornado intensity is best related to the magnitude of the vertical wind shear in the layer between the ground and 600 hPa. The results for this and other shear parameters are statistically highly significant when the data are grouped into two or three intensity classifications. Stability, as indicated by the “lifted index,” and midtropospheric relative humidity, correlate poorly with tornado intensity. The relationships established have application to tornado forecasting and nowcasting.

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