Answer:
Tornadoes can occur in any place that thunderstorms occur. The most active region for tornadoes is in in Kansas, Oklahoma, Texas, and Nebraska. Other hot spots for tornadoes are in Florida, Australia, South Africa, India, Bangladesh,and Argentina.
Most of the time in the Midwest is where air masses mostly meet. Although, they can form in other places too. In places like Massachusetts tornadoes are usually small.
As to when, tornadoes can form at any time of day or year, but are most common in late spring and early summer in the late afternoon and early evening.
In terms of conditions, tornadoes need thunderstorms to form in the presence of a variation of wind speed and direction with altitude (called wind shear). These thunderstorms typically form along a cold front (where cold air pushes into warm air) or dry line (where dry air pushes into moist air). However, they can form under other conditions such as in the outer bands of landfalling hurricanes.