General Guidelines for Estimating Wind Speeds
Calm Bft 0 |
Calm wind. Smoke rises vertically with little if any drift. |
1-3 mph 1-5 km/h Bft 1 |
Direction of wind shown by smoke drift, not by wind vanes. Little if any movement with flags. Wind barely moves tree leaves. |
4-7 mph 6-11 km/h Bft 2 |
Wind felt on face. Leaves rustle and small twigs move. Ordinary wind vanes move. |
8-12 mph 12-20 km/h Bft 3 |
Leaves and small twigs in constant motion. Wind blows up dry leaves from the ground. Flags are extended out. |
13-18 mph 21-29 km/h Bft 4 |
Wind moves small branches. Wind raises dust and loose paper from the ground and drives them along. |
19-24 mph 30-39 km/h Bft 5 |
Large branches and small trees in leaf begin to sway. Crested wavelets form on inland lakes and large rivers. |
25-31 mph 40-50 km/h Bft 6 |
Large brances in continous motion. Whistling sounds heard in overhead or nearby power and telephone lines. Umbrellas used with difficulty. |
32-38 mph 51-61 km/h Bft 7 |
Whole trees in motion. Inconvenience walking against the wind. |
39-46 mph 62-74 km/h Bft 8 |
Wind breaks twigs and small branches. Wind generally impedes walking. |
47-54 mph 75-87 km/h Bft 9 |
Structural damage occurs, such as chimney covers, roofing tiles blown off, and television antennas damaged. Ground is littered with many small twigs and broken branches. |
55-63 mph 88-101 km/h Bft 10 |
Considerable structural damage occurs, especially on roofs. Small trees may be blown over and uprooted. |
64-75 mph 102-120 km/h Bft 11 |
Widespread damage occurs. Larger trees blown over and uprooted. |
75+ mph >120 km/h Bft 12 |
Severe and extensive damage. Roofs can be peeled off. Windows broken. Trees uprooted. RVs and small mobile homes overturned. Moving automobiles can be pushed off the roadways. |