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Beaufort Wind 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.

Force Description Conditions Ashore Conditions Afloat Wind speed (knots)
0 Calm Smoke rises vertically Sea like a mirror 0
1 Light air Smoke drifts Ripples Only 1-3
2 Light breeze Leaves rustle; vane moved by wind Small wavelets not breaking 4-6
3 Gentle breeze Leaves in constant motion; light flag extend Large wavelets, crests begin to break 7-10
4 Moderate breeze Raises dust and loose paper; small branches move Small waves growing longer, fairly frequent white horses 11-16
5 Fresh breeze Small trees sway; crested wavelets on inland water Moderate waves taking more pronounced form; many white horses, perhaps some spray 17-21
6 Strong breeze Large branches in motion; whistling in telegraph Large waves forming; white foam crests more extensive, probably some spray 22-27
7 Near gale Whole trees in motion Sea heaps up; white foam streaks begin blowing from crests; very rough 28-33
8 Gale Breaks twigs off trees; impedes walking Moderatly high waves of greater length;crests break into spindrift with foamy streaks 34-40
9 Severe gale Slight structural damage to buildings High waves with tumbling crests; dense streaks of foam; spray may affect visibility 41-47
10 Storm Large branches broken; some trees uprooted Very high waves with long overhanging crests and dense streaks of foam making surface of the sea white; heavy tumbling sea 48-55
11 Violent Storm Very rarely experienced inland, widespread damage caused Exceptionally high waves; sea completly covered with long white patches of foam along direction of wind 56-63
12 Hurricane Very widespread damage Air filled with foam and spray; sea white with driving spray; visibility very seriously affected 64+