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Beaufort Wind Scales for Land.

Beaufort Wind Scales for Sea.

Beaufort Weather Notation.

Windchill Equivalent Temperature.

Beaufort Wind Scale (Land)

Beaufort

Number

Wind

Effect on land

Speed

(Knots)

Speed

(mph)

0

Calm

Smoke Rises Vertically

Less than 1

Less than

1

1

Light Air

Direction shown by smoke but not wind vanes

1-3

1-3

2

Light breeze

Wind felt on face; leaves rustle; wind vanes

move.

4-6

4-7

3

Gentle

breeze

Leaves & twigs in motion; wind extends light

flag

7-10

8-12

4

Moderate

breeze

Raises dust & loose paper; moves small

branches.

11-16

13-18

5

Fresh breeze

Small trees in leaf begin to sway.

17-21

19-24

6

Strong
breeze

Large branches in motion; whistling in

telegraph wires; difficulty with umbrellas.

22-27

25-31

7

Moderate

gale

Whole trees in motion; difficult to walk against

wind.

28-33

32-38

8

Fresh gale

Twigs break off trees; progress impeded.

34-40

39-46

9

Strong gale

Slight structural damage occurs; chimney pots

& slates blown off.

41-47

47-54

10

Whole gale

Trees uprooted and considerable structural

damage.

48-56

55-63

11

Storm

Widespread damage; seldom experienced in

UK.

57-65

64-75

12

Hurricane

Winds of this force rarely encountered outside

tropical revolving storms.

Over 65

Over 75

Beaufort Wind Scale (Sea)

Beaufort

Number

Wind

Effect on land

Speed

(Knots)

Wave

Height

(m)

0

Calm

Sea like a mirror.

Less than

1

0

1

Light Air

Ripples formed but without foam crests.

1-3

0.1

2

Light

breeze

Small wavelets; crests have glassy appearance but

do not break.

4-6

0.2

3

Gentle

breeze

Large wavelets. Crests begin to break. Perhaps

scattered white horses.

7-10

0.6

4

Moderate

breeze

Small waves becoming longer; fairly frequent white

horses.

11-16

1.0

5

Fresh

breeze

Moderate waves, taking more pronounced long form;

many white horses.

17-21

2.0

6

Strong
breeze

Large waves begin to form; the foam crests are more

extensive everywhere. (Probably some spray.)

22-27

3.0

7

Moderate

gale

Sea heaps up and white foam from breaking waves
begins to be blown in streaks along the direction of

wind.

28-33

4.0

8

Fresh gale

Moderately high waves of greater length; The foam is

blown into well marked streaks along direction of

wind.

34-40

5.5

9

Strong

gale

High waves. Crests begin to topple, tumble and roll

over. Spray may affect visibility.

41-47

7.0

10

Whole gale

Very high waves with long overhanging crests. The

sea takes on a white appearance. Visibility affected.

48-56

9.0

11

Storm

Exceptionally high waves. (Small & medium sized

ships may be lost to view behind waves.) Everywhere

the edges of wave crests are blown into froth.

Visibility affected.

57-65

11.5

12

Hurricane

The air is filled with foam & spray. Sea completely

white with driving spray; visibility seriously affected.

Over 65

>14

Beaufort Weather Notation

Weather

Beaufort
Notation

Weather

Beaufort
Notation

Blue Sky (0-2/8 cloud)

b

Snow

s

Overcast (Whole sky covered with
Unbroken cloud)

o

Fog

f

Partly Clouded (3/8 to 5/8 cloud)

bc

Thunder

t

Squally weather

q

Gale

g

Cloudy (6/8 to 8/8 cloud)

c

Thunderstorm with rain
or snow

tlr or tls

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Rain

r

Hail

h

Drizzle

d

Precipitation in sight

jp

Sleet

rs

Ugly threatening sky

u

Wet Air (no Precipitation)

e

Dust Haze

z

Unusual Visibility

v

Hoar Frost

x

Line squall

kq

Lightning

l

Dew

w

Dry air

y

Storm of drifting Snow

ks

Mist

m

Windchill Equivalent Temperature.

Beaufort

Force

Wind Speed
at 10 metre

height

Air Temperature °C

Knots

ms-1

-40

-35 -30 -25 -20 -15 -10

-5

0

5

10

15

1

2

0.8

-41

-36 -31 -26 -21 -15 -10

-5

0

+5

+10 +15

2

5

2.4

-43

-38 -32 -27 -22 -17 -12

-7

-1

+4

+9 +14

3

8.5

4.3

-47

-42 -37 -31 -26 -20 -15

-9

-4

+2

+7 +13

4

13.5

6.7

-52

-47 -41 -35 -30 -24 -18 -12

-7

-1

+5 +11

5

19

9.3

-57

-51 -45 -39 -33 -27 -21 -15

-9

-3

+3

+9

6

24.5

12.3

-61

-55 -49 -43 -37 -31 -24 -18 -11

-5

+2

+8

7

30.5

15.5

-65

-59 -52 -46 -40 -33 -27 -20 -13

-6

+0

+7

8

37

18.9

-68

-62 -55 -49 -42 -36 -29 -22 -15

-8

-1

+6

9

44

22.6

-72

-64 -59 -52 -45 -38 -31 -24 -17 -10

-2

+5

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"Windchill" is a term normally used to express the combined effect of low air temperature and of
wind on a standing or walking human. It can be measured by the rate of heat loss per unit area,

the "windchill factor" or more commonly by the "windchill equivalent temperature" (WET). No

allowance is made for precipitation or sea spray. Windchill does not apply to inanimate objects,

even heat producing engines. In "full" sunshine, a correction of about +7°C at low wind speeds and

+3°C at gale force should be made.

The concept is useful in countries which experience cold winters to distinguish the difference in

human comfort and risk of exposure between light and strong winds.

::Copyright J. Cranston::

2000 - 2006

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