A Tornado may or may not have a clearly defined funnel cloud. Smoke will rise vertically 1 - 3 Smoke will show slight direction but there is not enough wind to move a wind vane. You will feel a breeze on your face, smoke has definite direction, leaves move a bit and a wind vane will move. 8 - 12 Leaves will be in constant motion, small twig branches move, flags extend. 32 - 38 Large, whole trees in motion, becomes hard to walk totally upright against the wind.
Shingles begin to lift.
39 - 46 Green twigs begin to break off. You have to lean into the wind to walk. Shingles flap violently. TV antenna masts bend and antennas are destroyed. Structural damage starts getting serious.