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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

Wind Chill and Heat IndexMany Weather Stations show values for Wind Chill and Heat Index, but more often that not, these are not different from the current temperature. Why?This is because Wind Chill only applies when the average wind speed is above 4.8 kph and the temperature is below 10 degrees Celsius.Heat index only applies when the temperature is above 27 [...]

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