[Ref Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-23]
What’s funnel cloud, tornado and waterspout ?
All this three weather phenomena are high-speed vortex extending downward from the cumulonimbus base, and the difference is that:
- Funnel cloud does not reach the surface;
- Tornado touches a land surface;
- Waterspout touches a water surface
Formation of funnel cloud
Should the air being drawn into the cloud base of thunderstorms has any initial rotating motion, an extremely concentrated vortex could form and the wind in such a vortex can exceed 200 knots with pressure inside the vortex quite low. The strong winds gather dust and debris and the low pressure extending downward from the cumulonimbus base.