The Beaufort Wind Scale

The Beaufort Wind Scale was invented in 1805 by Rear-Admiral Sir Francis Beaufort of the British Royal Navy. Back then it referred to the amount of sail a ship could carry in specific wind conditions. During a light breeze, only one sail would be taken in, in a moderate gale seven would come down, and so on. Although the scale has been updated and modified several times, it's still widely used today to describe the wind's strength and speed.

It is very important to understand that wave heights listed here are for winds blowing across an unlimited fetch over open water.  This is often not the case on the Great Lakes, therefore wave heights on the Great Lakes may not be as high as listed in the Beaufort Scale and I have indicated that in the table below.  However, the state of the sea would match the given wind conditions well.

Meteorologists generally agree that in most cases, average waves reach an upper limit around 20 to 25 feet on the Great Lakes, though rogue waves can be higher.  Reporting these conditions will not likely come into play in spotters situations, because nobody should be out on the lake in conditions that produce those types of waves.  I have asterisked (***) the description of wave heights on the Beaufort scale  for those high wind conditions to limit the waves to "greater than 19 feet".  The Beaufort Scale for ocean conditions with unlimited fetch lists much higher waves. 


Beaufort scale

Description and
Speed ( knots)

Effects seen at sea or large lake.
Very dependent on fetch
for the Great Lakes

Effects seen on land

0 calm, less than 1 water is flat, like a mirror. smoke rises vertically
1 light air, 1-3 water is slightly rippled. smoke drifts, weather vanes are motionless
2 light breeze, 4-6 very small waves. breeze can be felt on face, weather vanes move a little, leaves rustle
3 gentle breeze, 7-10 waves larger, wave crests begin to break, occasional whitecaps possible. leaves are in motion constantly, light flags extend
4 moderate breeze, 11-16 waves roughly 1.5 - 4 feet, a lot of whitecaps. small branches begin to move, loose paper and dust can be raised
5 fresh breeze, 17-21 waves roughly 4 - 8 feet, many whitecaps, some spray. 4 foot waves more likely on the Great Lakes. tops of all trees are in motion, small trees are swayed
6 strong breeze, 22-27 waves roughly 8 - 13 feet, whitecaps everywhere, more spray. 8 foot waves are more likely on the Great Lakes. large tree branches begin to move, whistling is heard through wires
7 near gale, 28-33 waves roughly 13 - 19 feet, white foam from breaking waves blown along the line of the wind direction. 10 to 12 feet more likely on the Great Lakes. even large trees are in motion
8 gale, 34-40 waves still roughly 13 - 19 feet, but longer than at 7, wave crests begin to break into spin-drift, streaks of foam are seen everywhere. twigs can be broken off trees, walking is more difficult
9 strong gale, 41-47 *** waves are high, ~ 19 feet, water starts to roll, visibility affected by spray fences can be blown down, shingles can be blown from the roofs
10 storm, 48-55 *** very high waves, greater than 19 feet, heavily rolling water, overhanging crests, visibility strongly affected. not often experienced on land, trees will be broken or uprooted, damage in structures will be considerable
11 violent storm, 56-63 *** waves extremely high, water has  white appearance from foam patches. not experienced on land
12 hurricane, 64 and up *** waves are extremely high, air is filled with foam, water has a white appearance, visibility greatly reduced. not experienced on land

National Weather Service
Weather Forecast Office Buffalo
587 Aero Drive
Buffalo, N.Y. 14225-1405
(716) 565-0204 or (716) 565-0802

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Page last modified: June 13, 2006 at 1:25:00 AM
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