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Beaufort Scale

The Beaufort Scale was originally developed as a system for estimating wind strengths without the use of instruments. It was introduced in 1806 by Admiral Sir Francis Beaufort (1774-1857) of the British navy to describe wind effects on a fully rigged man-of-war sailing vessel, and it was later extended to include descriptions of effects on land features as well. It is currently still in use for this same purpose as well as to tie together various components of weather (wind strength, sea state, observable effects) into a unified picture.

The Beaufort scale is divided into a series of values, from 0 for calm winds to 12 and above for hurricanes. Each value represents a specific range and classification of wind speeds with accompanying descriptions of the effects on surface features.

Force

Description

Conditions

Wind speed (mph)

0

Calm

Smoke rises vertically

0

1

Light air

Smoke drifts

1-3

2

Light breeze

Leaves rustle; vane moved by wind

4-7

3

Gentle breeze

Leaves in constant motion; light flag extend

8-12

4

Moderate breeze

Raises duct and loose paper; small branches move

13-18

5

Fresh breeze

Small trees sway; crested wavelets on inland water

19-24

6

Strong breeze

Large branches in motion; whistling in telegraph

25-31

7

Moderate gale

Whole trees in motion

32-38

8

Fresh gale

Breaks twigs off trees; impedes walking

39-46

9

Strong gale

Slight structural damage to buildings

47-54

10

Whole gale

Large branches broken; some trees uprooted

55-63

11

Storm

Large trees uprooted

64-72

12

Hurricane

Widespread damage occurs

73+