THE BEAUFORT WIND SCALE

One of the first scales to estimate wind speeds and the effects was
created by Britain's Admiral Sir Francis Beaufort (1774-1857).  He
developed the scale in 1805 to help sailors estimate the winds via
visual observations. The scale starts with 0 and goes to a force of 12.
The Beaufort scale is still used today to estimate wind strengths.

The Beaufort scale:
    For use on land
    For use at sea

BEAUFORT SCALE: Specifications and equivalent speeds for use on land

FORCE  EQUIVALENT SPEED   DESCRIPTION      SPECIFICATIONS FOR USE ON LAND
     10 m above ground
     miles/hour  knots
0       0-1      0-1      Calm             Calm; smoke rises verticall.
1       1-3      1-3      Light air        Direction of wind shown by
                                           smoke drift, but not by wind
                                           vanes.
2       4-7      4-6      Light Breeze     Wind felt on face; leaves
                                           rustle; ordinary vanes moved
                                           by wind.
3       8-12     7-10     Gentle Breeze    Leaves and small twigs in
                                           constant motion; wind extends
                                           light flag.
4      13-18    11-16     Moderate Breeze  Raises dust and loose paper;
                                           small branches are moved.
5      19-24    17-21     Fresh Breeze     Small trees in leaf begin to
                                           sway; crested wavelets form on
                                           inland waters.
6      25-31    22-27     Strong Breeze    Large branches in motion;
                                           whistling heard in telegraph
                                           wires; umbrellas used with
                                           difficulty.
7      32-38    28-33     Near Gale        Whole trees in motion;
                                           inconvenience felt when walking
                                           against the wind.
8      39-46    34-40     Gale             Breaks twigs off trees;
                                           generally impedes progress.
9      47-54    41-47     Severe Gale      Slight structural damage occurs
                                           (chimney-pots and slates removed).
10     55-63    48-55     Storm            Seldom experienced inland; trees
                                           uprooted; considerable structural
                                           damage occurs.
11    64-72     56-63     Violent Storm    Very rarely experienced;
                                           accompanied by wide-spread damage.
12    73-83     64-71     Hurricane                        --
    For use on land
    For use at sea
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BEAUFORT SCALE: Specifications and equivalent speeds for use at sea

FORCE  EQUIVALENT SPEED   DESCRIPTION      SPECIFICATIONS FOR USE AT SEA
     10 m above ground
     miles/hour  knots
0       0-1      0-1      Calm             Sea like a mirror
1       1-3      1-3      Light air        Ripples with the appearance of
                                           scales are formed, but without
                                           foam crests.
2       4-7      4-6      Light Breeze     Small wavelets, still short,
                                           but more pronounced. Crests
                                           have a glassy appearance and
                                           do not break.
3       8-12     7-10     Gentle Breeze    Large wavelets. Crests begin
                                           to break. Foam of glassy
                                           appearance. Perhaps scattered
                                           white horses.
4      13-18    11-16     Moderate Breeze  Small waves, becoming larger;
                                           fairly frequent white horses.
5      19-24    17-21     Fresh Breeze     Moderate waves, taking a more
                                           pronounced long form; many
                                           white horses are formed.
                                           Chance of some spray.
6      25-31    22-27     Strong Breeze    Large waves begin to form; the
                                           white foam crests are more
                                           extensive everywhere.
                                           Probably some spray.
7      32-38    28-33     Near Gale        Sea heaps up and white foam
                                           from breaking waves begins to
                                           be blown in streaks along the
                                           direction of the wind.
8      39-46    34-40     Gale             Moderately high waves of greater
                                           length; edges of crests begin to
                                           breakinto spindrift. The foam is
                                           blown in well-marked streaks
                                           along the direction of the wind.
9      47-54    41-47     Severe Gale      High waves. Dense streaks of
                                           foam along the direction of the
                                           wind. Crests of waves begin to
                                           topple, tumble and roll over.
                                           Spray may affect visibility.
10     55-63    48-55     Storm            Very high waves with long over-
                                           hanging crests. The resulting
                                           foam, in great patches, is blown
                                           in dense white streaks along the
                                           direction of the wind.  On the
                                           whole the surface of the sea
                                           takes on a white appearance.
                                           The 'tumbling' of the sea becomes
                                           heavy and shock-like. Visibility
                                           affected.
11    64-72     56-63     Violent Storm    Exceptionally high waves (small
                                           and medium-size ships might be for
                                           a time lost to view behind the
                                           waves).  The sea is completely
                                           covered with long white patches
                                           of foam lying along the direction
                                           of the wind. Everywhere the edges
                                           of the wave crests are blown into
                                           froth. Visibility affected.
12    73-83     64-71     Hurricane        The air is filled with foam and
                                           spray. Sea completely white with
                                           driving spray; visibility very
                                           seriously affected.
    For use on land
    For use at sea
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Extracted from the Observers Handbook, Met Office


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Last Updated: 7th November 1997

Dave Wheeler weatherman@zetnet.co.uk

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