Wind Force Scale

In 1806, Sir Francis Beaufort developed a rating system for accurate recording of wind speed. This system was developed for sailors, but has since been modified by the National Weather Service for use on land.
 
Wind Speed (MPH)
Indicators
Terms Used in NWS Forecasts
0-1
 Calm; smoke rises vertically.
 Calm
1-3
Shown by direction of wind smoke drift, but not by wind vanes. 
Light
4-7 
Wind felt on face, leaves rustle; ordinary vanes moved by wind.
Light
8-12
Leaves and small twigs in constant motion; wind extends light flag.
Gentle
13-18
Raises dust and loose paper; small branches are moved.
Moderate
19-24
 Small trees in leaf begin to sway; crested wavelets form on inland waters.
 Fresh
25-31 
 Large branches in motion; whistling heard in telephone wires; umbrellas used with difficulty.
Strong
32-38
 Whole trees in motion; inconvenience felt walking against the wind.
Strong
39-46
 Breaks twigs off trees; generally impedes progress.
 Gale
47-54
Slight structural damage.
 Gale
55-63
 Seldom experienced inland; trees 
 uprooted; considerable structural damage occurs.
Whole gale
64-72
 Very rarely experienced inland; 
 accompanied by widespread damage.
Whole gale
73 or more
Very rarely experienced; accompanied by widespread damage.
Hurricane