A funnel cloud of a tornado contains of moist air. As it descends, the water vapor in it forms water droplets. The water droplets are not considered part of the cloud since they form within the funnel. The tornado is visible because of these droplets. The funnel is white because the droplets are white. The air on the ground is already moving because it's being pulled into the up current of the tornado. The winds are so strong that dust and debris start rotating with the tornado. Since the winds are so strong, it creates a great deal of noise almost like the engine of a freight train.
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