You may be aware of these, but they were new to me ...
NWS publishes a series of small books in pdf format for school age children. Download them at http://www.nws.noaa.gov/om/brochures.shtml
The one about Tornadoes, although it uses language suitable for young folks, has some fascinating facts:
"Most tornadoes happen in April, May, and June in the Central and Southeast United States. But they have occurred in every month and in every state."
"Oklahoma City has been struck by tornadoes about 32 times in the past 90 years."
"One town, Codell, Kansas, was struck threes times: In 1916, 1917 and 1918-each time on May 20."