National Weather Service United States Department of Commerce



Pictures from around western Colorado and eastern Utah



(Red indicates Severe Weather Criteria)

1/4" Pea Size
3/4" Penny Size
7/8" Nickel Size
1" Quarter Size
1 1/4" Half Dollar Size
1 1/2" Walnut or Ping Pong Ball Size
1 3/4" Golf Ball Size
2" Hen Egg Size
2 1/2" Tennis Ball Size
2 3/4" Baseball Size
3" Teacup Size
4" Grapefruit Size
4 1/2" Softball Size

Beaufort Wind Scale


Force Wind
Appearance of Wind Effects
On the Water On Land
0 < 1 Calm Sea surface smooth and mirror-like Calm, smoke rises vertically
1 1-3 Light Air Scaly ripples, no foam crests Smoke drift indicates wind direction, still wind vanes
2 4-6 Light Breeze Small wavelets, crests glassy, no breaking Wind felt on face, leaves rustle, vanes begin to move
3 7-10 Gentle Breeze Large wavelets, crests begin to break, scattered whitecaps Leaves and small twigs constantly moving, light flags extended
4 11-16 Moderate Breeze Small waves 1-4 ft. becoming longer, numerous whitecaps Dust, leaves, and loose paper lifted, small tree branches move
5 17-21 Fresh Breeze Moderate waves 4-8 ft taking longer form, many whitecaps, some spray Small trees in leaf begin to sway
6 22-27 Strong Breeze Larger waves 8-13 ft, whitecaps common, more spray Larger tree branches moving, whistling in wires
7 28-33 Near Gale Sea heaps up, waves 13-20 ft, white foam streaks off breakers Whole trees moving, resistance felt walking against wind
8 34-40 Gale 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, resistance felt walking against wind
9 41-47 Strong Gale 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 48-55 Storm 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 56-63 Violent Storm Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced  
12 64+ Hurricane Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced  
  * World Meteorological Organization

Rear-Admiral, Sir Francis Beaufort, Knight Commander of the Bath, was born in Ireland in 1774. He entered the Royal Navy at the age of 13 as a midshipman aboard the Aquilon. Beaufort had an illustrious career on the seas and by 1800 had risen to the rank of Commander. In the summer of 1805 Commander Beaufort was appointed to the command of the Woolwich, a 44 cannon man-of-war. It was at this time that he devised his wind force scale.

Cartooon image of a red flag

In examining Beaufort's original scale, it is a force scale with no mention of wind speed. Beaufort's original specification is essentially an association of a set of values (0 to 12) with a description of the state and behavior of a "well-conditioned man-of-war."

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. By 1955, wind velocities in knots replaced Beaufort numbers on weather maps. But there was still a need for eyeball estimates by seamen to fill the gaps in the global observing network. Thus it became imperative to relate the seaman's observations logged in Beaufort numbers to the wind speed in knots. And so Beaufort's scale had transformed itself from a tool of the mariner to a means for the meteorologist.