National Climatic Data Center. NOAA Severe Weather Data Inventory. Storm Events Database. Tornado Climatology. Monthly Tornado Occurrence Maps January | February | March | April | May | June | July | August | September | October | November | December Because a tornado is part of a severe convective storm, and these storms occur all over the Earth, tornadoes are not limited to any specific geographic location.
In fact, tornadoes have been documented in every state of the United States, and on every continent, with the exception of Antarctica (even there, a tornado occurrence is not impossible). In fact, wherever the atmospheric conditions are exactly right, the occurrence of a tornadic storm is possible. See NOAA's National Severe Storms Laboratory (NSSL) Severe Weather 101 information for more on the conditions necessary for tornado formation.