Beaufort Wind Force Scale

Developed in 1805 by Sir Francis Beaufort of England

Rear-Admiral, Sir Francis Beaufort, was born in Ireland in 1774. He entered the Royal Navy at the age of 13 and was a midshipman aboard the Aquilon.
By 1800 he had risen to the rank of Commander. In the summer of 1805 Beaufort was appointed to the command of the Woolwich, a 44 gun man-of-war.

In 1806 he wrote in his log book a wind force scale. The scale was simple and very similar to one that Alexander Dalrymple had written in a book in 1789.
A year later he added some criteria to the 0-12 scale that indicated how much of a ship's sails would be employed by a British man-of-war under each condition.
It was not related to the speed of the wind.

Over the following years he continued to use his scale in his logs. It was finally adopted in December 1838 by the British Admiralty for use in all Royal Navy logbooks.
However, as ship design and the introduction of steam power became widespread even that scale had to be modified.

In 1912 the International Commission for Weather Telegraphy sought some agreement on velocity equivalents for the Beaufort scale. A uniform set of equivalents was accepted in 1926
and revised slightly in 1946, extending the scale to 17 values (the added five values further refining the hurricane-force winds). By 1955, wind velocities in knots replaced Beaufort numbers on weather maps.

Today's Beaufort Scale including the observed land conditions...



Force Wind
(Knots)
Wind
(MPH)
Appearance of Wind Effects
On the Water On Land
0 Calm Less than 1 Calm Sea surface smooth and mirror-like Calm, smoke rises vertically
1 Light Air 1-3 1.2 - 3.0 Scaly ripples, no foam crests Smoke drift indicates wind direction, still wind vanes
2 Light Breeze 4-6 3.7 - 7.5 Small wavelets, crests glassy, no breaking Wind felt on face, leaves rustle, ordinary vane moved by wind.
3 Gentle Breeze 7-10 8.0 - 12.5 Large wavelets, crests begin to break, scattered whitecaps Leaves and small twigs constantly moving, light flags extended
4 Moderate Breeze 11-16 13.0 - 18.6 Small waves 1-4 ft. becoming longer, numerous whitecaps Dust, leaves, and loose paper lifted, small tree branches move
5 Fresh Breeze 17-21 19.3 - 25.0 Moderate waves 4-8 ft taking longer form, many whitecaps, some spray Small trees in leaf begin to sway
6 Strong Breeze 22-27 25.5 - 31.0 Larger waves 8-13 ft, whitecaps common, more spray Larger tree branches moving, whistling in wires
7 Near Gale 28-33 32.0 - 38.0 Sea heaps up, waves 13-20 ft, white foam streaks off breakers Whole trees moving, resistance felt walking against wind
8 Gale 34-40 39.0 - 46.0 Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks Whole trees in motion, generally impedes progress walking against wind
9 Strong Gale 41-47 47.0 - 55.0 High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility Slight structural damage occurs, slate blows off roofs
10 Storm 48-55 56.0 - 64.0 Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility Seldom experienced on land, trees broken or uprooted, "considerable structural damage"
11 Violent Storm 56-63 65.0 - 74.0 Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced Widespread damage, very rarely experienced.
12 Hurricane 64+ 75+ Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced  


Back to Station Info