Tornadoes form in regions of the atmosphere that have abundant warm and moist air near the surface with drier air above, a change in wind speed and direction with height, and weather systems such as fronts that force air upward. The United States provides these three ingredients in abundance, so it is not surprising that the majority of the world’s reported tornadoes occur in the USA. Within the United States, tornadoes can occur in nearly every state and in every month of the year. Wisconsin has experienced tornadoes in every month except February. It is generally accepted that tornado season begins in the springtime— and that is now.
Tornado season is based on when the ingredients for severe weather come together in a particular place. Because a change in wind with height is closely related to the presence of a jet stream, tornado season moves north and south during the year with a jet stream. Tornado season peaks in March and April in the Southeast but not until July in the upper Midwest and Northeast. The deep South has a secondary peak in tornado occurrence in November.
Tornadoes can also happen at any time of day or night. However, they thrive on solar heating and in some cases the ability of warm, moist air at the surface to penetrate the capping inversion. Therefore, the most likely times for tornadoes are late afternoon or early evening. More than half of all U.S. tornadoes occur during the hours of 3:00 PM to 7:00 PM local time.