Beaufort Wind Scale

The Beaufort scale /ˈboʊfərt/ is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort wind force scale. The scale was devised in 1805 by Francis Beaufort (later Rear Admiral Sir Francis Beaufort), an Irish Royal Navy officer, while serving in HMS Woolwich.

 

ForceWind (Knots)WMO ClassificationAppearance of Wind on WaterAppearance of Wind on Land
0<1CalmSea surface smooth and mirror-likeCalm, smoke rises vertically
11-3Light AirScaly ripples, no foam crestsSmoke drift indicates wind direction, still wind vanes
24-6Light BreezeSmall wavelets, crests glassy, no breakingWind felt on face, leaves rustle, vanes begin to move
37-10Gentle BreezeLarge wavelets, crests begin to break, scattered whitecapsLeaves and small twigs constantly moving, light flags extended
411-16Moderate BreezeSmall waves 1-4 ft. becoming larger, numerous whitecapsDust, leaves and loose paper lifted, small tree branches move
517-21Fresh BreezeModerate waves 4-8 ft. taking longer form, many whitecaps, some spraySmall trees in leaf begin to sway
622-27Strong BreezeLarger waves 8-13 ft. whitecaps common, more sprayLarger tree branches moving, whistling in wires
728-33Near GaleSea heaps up, waves 13-20 ft. white foam streaks off breakersWhole trees moving, resistance felt walking against wind
834-4-GaleModerately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaksWhole trees in motion, resistance felt walking against wind
941-47Strong GaleHigh waves (20 ft.), sea begins to roll, dense streaks of foam, spray may reduce visibilitySlight structural damage occurs, slate blows of roofs
1048-55StormVery high waves (20-30 ft.), with overhanging crests, sea white with densely blown foam, heaving rolling, lowered visibilitySeldom experienced on land, trees broken or uprooted, "considerable structural damage"
1156-63Violent StormExceptionally high (30-45 ft.) waves, foam patches cover sea, visibility more reduced
1264+HurricaneAir filled with foam, waves over 45 ft., sea completely white with driving spray, visibility greatly reduced