An Augmented Tornado Climatology

Abstract

Careful screening of the National Severe Storms Forecast Center's tornado log eliminated almost 20% of the reports as doubtful, leaving 17 659 tornadoes during 27 years, 1950?76 (654 annually). Newspaper accounts and other local information provided intensifies (Fujita wale) for all but 2346 tornadoes and path lengths for all but 2011 tornadoes. There were 14 409 tornadoes for which both intensity and path length estimates were made. Of these, 61.7% were weak (<112 mph), 36% strong (113?206 mph), and only 2.3% violent (207?318 mph). However, the 340 violent tornadoes caused 68% of the 3070 fatalities attributed to tornadoes for which force estimates could he made (113.7 annually). Most violent tornadoes came in swarms except in southeastern United States, where no day had mart than one. Some 61% of the violent tornadoes had intermediate paths (3.2?31 mi), while 73% of weak and strong tornadoes had short paths. Violent tornadoes occurred at all times of day and night, while weak and strong tornadoes showed diurnal trends. May and June accounted for 40.8% of all tornadoes. Other aspects of tornado climatology are shown in tables, diagrams and maps of average annual incidence normalized to 10 000 mi2 area per year.