Beaufort Scale (Wind Speed)

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Etymology: Sir Francis Beaufort: a scale in which the force of the wind is indicated by numbers from 0 to 12.

BEAUFORT
NUMBER
NAME WIND SPEED
MPH
WIND SPEED
KPH
DESCRIPTION
0 calm <1 <1 calm; smoke rises vertically
1 light air 1-3 1-5 direction of wind shown by smoke but not by wind vanes
2 light breeze 4-7 6-11 wind felt on face; leaves rustle; wind vane moves
3 gentle breeze 8-12 12-19 leaves and small twigs in constant motion; wind extends light flag
4 moderate breeze 13-18 20-28 wind raises dust and loose paper; small branches move
5 fresh breeze 19-24 29-38 small-leaved trees begin to sway; crested wavelets form on inland waters
6 strong breeze 25-31 39-49 large branches move; overhead wires whistle; umbrellas difficult to control
7 moderate gale or near gale 32-38 50-61 whole trees sway; walking against wind is difficult
8 fresh gale or gale 39-46 62-74 twigs break off trees; moving cars veer
9 strong gale 47-54 75-88 slight structural damage occurs; shingles may blow away
10 whole gale or storm 55-63 89-102 trees uprooted; considerable structural damage occurs
11 storm or violent storm 64-72 103-117 widespread damage occurs
12 hurricane* 72> 117> widespread damage occurs

*The U.S. uses 74 statute mph as the speed criterion for a hurricane.

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