Using the National Weather Service Southern Region Headquarters web site, you can view information on tornadoes have occured in Tulsa County between the years 1875 - 2010.
Between the years 1953 - 2004, an average of 57 struck Oklahoma each year.
The Tulsa Area Management Agency's emergency operations center controls 75 sirens to warn people about tornadoes, flash flood and attacks during war. All are three minutes long. A tornado warning is a steady, high pitched tone; flash flood is an alternating high-low signal; the attack is an unbroken, wavering signal.
The Fujita, or F-Scale, was developed in 1971 by T. Theodore Fujita of the University of Chicago. The original scale was updated in 2007. The updated scale, known as the Enhanced F-Scale, is set of wind-speed estimates - not measurements - based on damage surveys. Its estimates at the point of damage are based on a judgement of eight levels of damage indicators.
The Enhanced F-Scale:
The original F-Scale: