Beaufort Wind Scale

Developed in 1805 by Sir Francis Beaufort of England, the Beaufort Scale is an empirical measure for describing wind speed based mainly on observed sea conditions (on land it is categorised by the physical effects it has on vegetation and structures). Its full name is the Beaufort Wind Force Scale.
The scale was created in 1806 by Sir Francis Beaufort, an Irish-born British admiral and hydrographer. The scale that carries Beaufort's name had a long and complex evolution, from the previous work of others, to when Beaufort was a top administrator in the Royal Navy in the 1830s. In the early 19th Century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective - one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in standardizing the scale.

Force Wind
Appearance of Wind Effects
0 < 1 Calm Calm, smoke rises vertically
1 1-3 Light Air Direction of wind shown by smoke drift, but not by wind vanes.
2 4-7 Light Breeze Wind felt on exposed skin. Leaves rustle, vanes begin to move.
3 8-12 Gentle Breeze Leaves and small twigs in constant motion, light flags extended.
4 13-18 Moderate Breeze Dust and loose paper raised. Small branches begin to move.
5 19-24 Fresh Breeze Branches of a moderate size move. Small trees in leaf begin to sway.
6 25-31 Strong Breeze Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.
7 32-38 Near Gale Whole trees in motion. Effort needed to walk against the wind.
8 39-46 Gale Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
9 47-54 Strong Gale Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.
10 55-63 Storm Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.
11 64-72 Violent Storm Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.
12 72-83 Hurricane Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.