Tornado Documentation

Tornadoes in northeast Iowa, southeast Minnesota, and southwest and central Wisconsin
Background Information	Statistics (1850-Present)	Records (1850-Present)

Tornado Documentation History

The following information came from Thomas P. Grazulis's Significant Tornadoes 1680-1991 (page 6):

1) Historic Period (pre-1880: A few researchers in the 19th Century did create short lists of tornadoes, notably Elias Loomis in 1842. The work of early meteorologists, along with descriptions of pre-1871 tornadoes, was documented by David Ludlum (1970) in Early American Tornadoes, 1586-1870. In 1884, John Park Finley published a list of 600 tornadoes, most of them during the 1877-1882 time span.
2) Early Period (1880-1915): This period was documented irregularly and with almost no consistency in several different government and meteorological publications.

3) Middle Period (1916-1949): The official counting of tornadoes began in 1916, as part of the Report of the Chief of the Weather Bureau. The evolution of the present day documentation in Storm Data can be traced back to a format change in 1930, when tabular data replaced a paragraph format. The location of the tornado list changed to the United States Meteorological Yearbook in 1935, but the format was unchanged. The annual number of tornadoes gradually increased from 90 in 1916 to 249 in 1949 about one-fourth of current totals. Most of those recorded tornadoes were very destructive and/or widely visible. The seriousness of the documentation effort varied from state to state. It was adequate, for significant tornadoes, in Kansas and Iowa. It was almost non-existent for many years in Nebraska and the Dakotas.

4) NSSFC Data Base Period (1950-present): As listed on the computerized data base at the National Severe Storms Forecast Center (NSSFC) in Kansas City, Missouri. The year 1950 marked a format change and a listing of tornadoes in Climatological Data National Summary. This evolved, by 1959, into the present day Storm Data format.

5) Modern Period (1953-present): Serious efforts to count all tornadoes did not begin until the first full year of Weather Bureau (became the National Weather Service in the 1980s) tornado watches in 1953. The subsequent verification efforts boosted the number of tornadoes from an average of 227 (1948-1952) to 585 (1953-1957). The 1953-1991 average has risen to 768 tornadoes per year .