TORNADO PROBABILITIES

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  • 1 Office of Climatology, U.S. Weather Bureau, Washington D.C.
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Abstract

The frequency distributions of tornado path width and length are developed using data series from Iowa and Kansas. From these, the distribution of path area is derived. Direction of path and annual frequency are discussed. It is found that all but about 1 percent of Iowa tornadoes had path directions toward the northeast and southeast quadrants. The annual frequency for a group of Iowa counties is found to have a negative binomial distribution indicating that the climatological series is formed from a Polya stochastic process. This resembles the situation for other types of storms where the events tend to cluster. A new map of annual frequency for the United States is presented for the period 1953–62, during which it is believed tornado observation was fairly stable. The expected value of tornado area is derived from the area distribution. From this and the annual frequency, the probability of a tornado striking a point is found.

Abstract

The frequency distributions of tornado path width and length are developed using data series from Iowa and Kansas. From these, the distribution of path area is derived. Direction of path and annual frequency are discussed. It is found that all but about 1 percent of Iowa tornadoes had path directions toward the northeast and southeast quadrants. The annual frequency for a group of Iowa counties is found to have a negative binomial distribution indicating that the climatological series is formed from a Polya stochastic process. This resembles the situation for other types of storms where the events tend to cluster. A new map of annual frequency for the United States is presented for the period 1953–62, during which it is believed tornado observation was fairly stable. The expected value of tornado area is derived from the area distribution. From this and the annual frequency, the probability of a tornado striking a point is found.

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