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Beaufort Wind Scale
Wind speed is measured by using a scale of 0-12 based on visual clues originally developed in 1806 by Sir Francis Beaufort. He developed a rating system to make accurate recording of wind speed. This system was developed for sailors, but has since been modified by the National Weather Service for use on land.

Beaufort
Force
Wind Speed
(KmPH)
Wind Speed
(MPH)
Indicators Terms Used in NWS Forecasts
0 0-2 0-1 Calm; smoke rises vertically. Calm
1 2-5 1-3 Shown by direction of wind smoke drift, but not by wind vanes. Light
2 6-12 4-7 Wind felt on face, leaves rustle; ordinary vanes moved by wind. Light
3 13-20 8-12 Leaves and small twigs in constant motion; wind extends light flag. Gentle
4 21-29 13-18 Raises dust and loose paper; small branches are moved. Moderate
5 30-39 19-24 Small trees in leaf begin to sway; crested wavelets form on inland waters. Fresh
6 40-50 25-31 Large branches in motion; whistling heard in telephone wires; umbrellas used with difficulty. Strong
7 51-61 32-38 Whole trees in motion; inconvenience felt walking against the wind. Strong
8 62-74 39-46 Breaks twigs off trees; generally impedes progress. Gale
9 75-87 47-54 Slight structural damage. Gale
10 88-101 55-63 Seldom experienced inland; trees uprooted; considerable structural damage occurs. Whole gale
11 102-116 64-72 Very rarely experienced inland; accompanied by widespread damage. Whole gale
12 117 or more 73 or more Very rarely experienced; accompanied by widespread damage. Hurricane

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