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 |
Widespread damage occurs |
73+ |
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