The Storm Prediction Center (SPC) maintains a database containing information about every tornado reported in the United States. Data goes back through 1950. During the 51 years of record, there have been many changes in tornado reporting efficiency. These have resulted in an increase of approximately 23 storms each year (Fig. 1). While the year-to-year changes are small, when they are integrated over a half-century their effect is marked! Further, the changes are not linear; rather, there are marked discontinuities in the time trend. These changes are more likely a product of changes in American society than in the actual tornado climatology (Schaefer and Brooks, 2000). For instance, cellular phones, which are now common place but unknown in the 1950's, make it much more likely that people will report a tornado that they observe while they are traveling.
[1]
James R. McDonald,et al.
Tornado: an engineering-oriented perspective
,
1977
.
[2]
Charles A. Doswell,et al.
On Some Issues of United States Tornado Climatology
,
1988
.
[3]
Tetsuya Theodore. Fujita,et al.
"Use of Tornado Path Lengths and Gradations of Drainage to Assess Tornado Intensity Probabilities," by Abbey, Robert and Fujita, T. Theodore, Preprints, 9th Conference on Severe Local Storms, Norman, American Meteorological Society, Boston, p. 286-293, 1975.
,
1975
.
[4]
Joseph T. Schaefer,et al.
A Minimum Assumption Tornado-Hazard Probability Model
,
1986
.