"1. moisture (water vapor) in the air near the surface 2. instability - relatively large decrease of air temperature with height 3. lift - some process (such as a front) that forces air to rise"
The air is dry during the summer and any moisture amount is increased in the afternoon as the temperature cools.
The tornadoes in the USA occur mainly during the summer afternoons because the excess warming of ocean water in summer afternoons warms up the air right above the water and stimulates a cycle of vertical circulation of air resulting in the generation of a tornado.
<u>Explanation:</u>
When the air near the ocean surface warms up, it becomes light and rises above the heavier packet of air.
This action happens in a continuous loop and eventually results in the generation of a tornado.
