Beaufort scale

1. n. [Geophysics]
The 0 to 12 scale for measurement of wind strength according to its effect on objects such as trees, flags and water established by Admiral Francis Beaufort (1774 to 1857). According to the Beaufort scale, at wind speeds below 1 knot or 1 km/hr, seas are calm. Whitecaps on water and blowing dust and leaves correspond to a Beaufort number of 4, with winds of 11 to 16 knots [20 to 28 km/hr]. Hurricane-force winds, greater than 64 knots [> 118 km/hr], have a Beaufort number of 12.