Page 37 - CCPS Monograph - Natural Hazards

APPENDIX G: EXPLANATION OF TERMS

The Beaufort wind scale is a system used to estimate and report wind speeds when no measuring
apparatus is available. It was invented in the early 19th Century by Admiral Sir Francis Beaufort of the
British Navy as a way to interpret winds from conditions at sea. Since that time, the scale has been
modernized for effects on land. (Weather 2019)

Table G.1 Beaufort Wind Scale (adapted from Weather 2019a)

Force Speed Description Specifications for use at sea
kph (mph) knots Specifications for use on land
0 0-1.6 0-1 Calm Sea like a mirror.
(0-1) Calm; smoke rises vertically.
1 1.6-4.8 1-3 Light Air Ripples with the appearance of scales are formed,
(1-3) but without foam crests.
Direction of wind shown by smoke drift, but not by
wind vanes.
2 6.4-11.3 4-6 Light Small wavelets, still short, but more pronounced.
(4-7) Breeze Crests have a glassy appearance and do not break.
Wind felt on face; leaves rustle; ordinary vanes
moved by wind.
3 12.9-19.3 7-10 Gentle Large wavelets. Crests begin to break. Foam of
(8-12) Breeze glassy appearance. Perhaps scattered white
horses.
Leaves and small twigs in constant motion; wind
extends light flag.
4 20.9-29.0 11-16 Moderate Small waves, becoming larger; fairly frequent white
(13-18) Breeze horses.
Raises dust and loose paper; small branches are
moved.
5 30.6-38.6 17-21 Fresh Moderate waves, taking a more pronounced long
(19-24) Breeze form; many white horses are formed.
Small trees in leaf begin to sway; crested wavelets
form on inland waters.
6 40.2-49.9 22-27 Strong Large waves begin to form; the white foam crests
(25-31) Breeze are more extensive everywhere.
Large branches in motion; whistling heard in
telegraph wires; umbrellas used with difficulty.
7 51.5-61.2 28-33 Near Gale Sea heaps up and white foam from breaking
(32-38) waves begins to be blown in streaks along the
direction of the wind.
Whole trees in motion; inconvenience felt when
walking against the wind.
8 62.8-74.0 34-40 Gale Moderately high waves of greater length; edges of
(39-46) crests begin to break into spindrift. The foam is
blown in well-marked streaks along the direction
of the wind.
Breaks twigs off trees; generally impedes progress.

Assessment of and planning for natural hazards 34

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