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Beaufort Scale

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Beaufort Scale

Your weather station may measure wind speed, and if it does it will tell you quite precisely how fast the wind is blowing in km/h or knots or whatever your favourite measure is.. But how fast is that? What does that feel like?

Originating in 1805 the Beaufort scale puts a description to a speed, starting with calm, through breezes to gales and up to hurricanes by way of a number between 0 and 12.

Whilst 40km/h may sound pretty strong, it measures up as 6 on the Beaufort scale - large branches will move, but you may still be able to use your umbrella. Here is a table of what it feels like:

Beaufort number Description Wind speed Wave height Sea conditions Land conditions
0 Calm < 1 knot
< 2 km/h
0 m Sea like a mirror Smoke rises vertically.
1 Light air 1–3 knots
2–5 km/h
0-0.3m Ripples with appearance of scales are formed, without foam crests Direction shown by smoke drift but not by wind vanes.
2 Light breeze 4–6 knots
6–11 km/h
0.3–0.6 m Small wavelets still short but more pronounced; crests have a glassy appearance but do not break Wind felt on face; leaves rustle; wind vane moved by wind.
3 Gentle breeze 7–10 knots
12–19 km/h
0.6–1.2 m Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses Leaves and small twigs in constant motion; light flags extended.
4 Moderate breeze 11–16 knots
20–28 km/h
1–2 m Small waves becoming longer; fairly frequent white horses Raises dust and loose paper; small branches moved.
5 Fresh breeze 17–21 knots
29–38 km/h
2–3 m Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray Small trees in leaf begin to sway; crested wavelets form on inland waters.
6 Strong breeze 22–27 knots
39–49 km/h
3–4 m Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
7 High wind,
moderate gale,
near gale
28–33 knots
50–61 km/h
4–5.5 m Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen Whole trees in motion; inconvenience felt when walking against the wind.
8 Gale,
fresh gale
34–40 knots
62–74 km/h
5.5–7.5 m Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind Twigs break off trees; generally impedes progress.
9 Strong/severe gale 41–47 knots
5–88 km/h
7–10 m High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility Slight structural damage (chimney pots and slates removed).
10 Storm,
whole gale
48–55 knots
89–102 km/h
9–12.5 m Very high waves with long overhanging crests; 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; rolling of the sea becomes heavy; visibility affected Seldom experienced inland; trees uprooted; considerable structural damage.
11 Violent storm 56–63 knots
103–117 km/h
11.5–16 m Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected Very rarely experienced; accompanied by widespread damage.
12 Hurricane force ≥ 64 knots
≥ 117km/h
≥ 16m The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected Devastation.

Wind Chill and Heat Index

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