Final answer:
The correct answer is option a) Touch the ground.
Step-by-step explanation:
To be classified as a tornado by the U.S. National Weather Service, a funnel cloud must touch the ground. This is because a tornado is defined as a violent rotating column of air extending from a thunderstorm to the ground, which can cause damage to structures, vehicles, and vegetation.
Tornadoes typically form from severe thunderstorms called supercells, which contain a rotating column of air. When the rotating air column shifts to spin around a vertical axis due to differences in wind speeds at different altitudes, a tornado can develop. The most intense tornadoes can produce wind speeds as high as 500 km/h, and they are notorious for their ability to lift and tear apart structures, even driving straw through tree trunks.
Meteorologists use changes in wind velocity and atmospheric pressure to predict tornadoes, as conditions with greater atmospheric rotation are more likely to produce these powerful storms. The barometric pressure is a key factor in storm formation, with a large pressure difference between two areas being a critical criterion for tornado potential.