Beaufort's Wind Scale
The Beaufort wind scale, which is used to describe the force of the wind, was invented by Admiral Beaufort in 1805. With some experience with the use of the scale the wind force can be estimated with reasonable accuracy.
The Beaufort wind scale is divided into series of values, from zero for calm winds, up to twelve and above for hurricanes. Each value represents a specific range and a classification of wind velocity with an accompanying descriptions of the effects on surface features.
| Beaufort No. | Description of wind | Observation | Mean Wind Speed (knots) |
|---|---|---|---|
| 0 | Calm | Smoke rises vertically. The sea is mirror smooth. | 0 - 1 |
| 1 | Light Air | Direction of wind shown by smoke drift but not by vanes. Scale-like ripples on sea, no foam on wave crests. | 1 - 3 |
| 2 | Light Breeze | Wind felt on face, leaves rustle, ordinary vanes moved by wind. Short wavelets, glassy wave crests. | 4 - 6 |
| 3 | Gentle Breeze | Leaves and small twigs in constant motion, wind extends light flag | 7 - 10 |
| 4 | Moderate Breeze | Raises dust and loose paper, small branches moved. Fairy frequent whitecaps occur. | 11 - 16 |
| 5 | Fresh Breeze | Small trees in leaf begin to sway. Moderate waves, many white foam crests. | 17 - 21 |
| 6 | Strong Breeze | Large branches in motion, whistling heard in telegraph wires. Some spray on the sea surface. | 22 - 27 |
| 7 | Moderate (Near) gale | Whole trees in motion, inconvenience felt when walking into wind. Foam on waves blows on streaks. | 28 - 33 |
| 8 | Gale | Twigs broken of trees, generally impeded progress. Long streaks on foam appear on sea. | 34 - 40 |
| 9 | Strong gale | Straight structural damage, e.g. slates and chimney pots removed from the roofs. High waves, crest start to roll over. | 41 - 47 |
| 10 | Storm | Trees uprooted, considerable structural damage. Exceptionally high waves, visibility affected. | 48 - 55 |
| 11 | Violent Storm | Widespread damage | 56 - 63 |
| 12 | Hurricane | Air is filled with spray and foam. | > 64 |
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