Relationship of Tornado Deaths to Severe Weather Watch Areas

Abstract

The National Severe Storm Forecast Center (NSSFC) has complied statistics on tornado occurrences for the period 1950?1973 which not only include date, time, and location, but a variety of information such as deaths, injuries, damage class, and other descriptive features on each event. This study relates tornado deaths to the severe weather watches issued by the Severe Local Storms Forecast Unit (SELS) from the inception of the Unit in March 1952 through 1973. Some 14 600 tornadoes occurred during this period, but only 497 of the total caused fatalities. The total tornado-related deaths were 2575. The percentage of the tornadoes which caused deaths within the time and space of a watch is presented by year, as is the overall correctness (56%) for the entire period. Of the total tornado deaths, the percentage within valid watch areas is shown for each year together with the overall percentage for the period (66%). Statistics were computed on two lead times. One starts with the issuance time of a watch and the other starts with the valid time of the watch (both of which are indicated on the watch message), while both lead times end with the occurrence of a tornado producing death(s). The average lead times in hours and minutes were 3:16 and 2:33 respectively. Likewise, an investigation was made as to tornado deaths outside watch areas with respect to time of day and geographical location. While there appeared to be no relationship between these deaths and time of day, six southeastern states accounted for 48% of the total. An interesting corollary presented reveals that 235 of the 497 death producing tornadoes caused only a single fatality, while 26 tornadoes accounted for 1180 deaths. The statistics presented on tornado deaths and severe weather watches imply a comparatively high skill in forecasting severe weather. This is true in the area of major tornado outbreaks as compared to the isolated tornado occurrence. Two-thirds of all deaths from tornadoes in the period of study occurred with major outbreaks and 77% of these deaths were within watch areas.