Beaufort Scale (for wind speed)

The Beaufort scale is a standard scale to communicate wind force.  The scale starts at traditionally ranges from 0 to 12, with zero been no wind and 12 been a hurricane force wind of over 120km/h.  The scale has since grown to 17, to describe more severe hurricane winds.  For the sake of this article I have just included the 0-12.  The scale include descriptions of the what to expect to see from such a force. 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 relate 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…

Beaufort	Wind speed		Description	Land conditions
	kt	km/h
0	0	0	Calm	Calm. Smoke rises vertically.
1	1-3	1-6	Light air	Wind motion visible in smoke.
2	4-6	7-11	Light breeze	Wind felt on exposed skin. Leaves rustle.
3	1-10	12-19	Gentle breeze	Leaves and smaller twigs in constant motion.
4	11-15	20-29	Moderate breeze	Dust and loose paper raised. Small branches begin to move.
5	16-21	30-39	Fresh breeze	Smaller trees sway.
6	22-27	40-50	Strong breeze	Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult.
7	28-33	51-62	Near gale	Whole trees in motion. Effort needed to walk against the wind.
8	34-40	63-75	Gale	Twigs broken from trees. Cars veer on road.
9	41-47	76-87	Strong gale	Light structure damage.
10	48-55	88-102	Storm	Trees uprooted. Considerable structural damage.
11	56-63	103-119	Violent storm	Widespread structural damage.
12	64-80	>120	Hurricane	Considerable and widespread damage to structures.