Surface Wind

Question 1

How is wind direction (direction from which the wind is blowing) reported?

Answer 1

Usually taken as the mean surface wind direction over the previous 10 minutes (Except when a marked discontinuity occurs), measured in tens of degrees (Between 010 and 360) from True North.

N.B.

• Rounded to nearest 10 degrees.
• Directions of 005, 015, etc should be rounded down.

Question 2

What is a marked discontinuity?

Answer 2

A change in the mean surface wind direction of 30 degrees or more with a mean speed of 10 knots or more before or after the change.

or

An increase or decrease in the wind speed of 10 knots or more sustained for at least 2 minutes.

In either of these cases, the mean direction or speed over the previous 2 minutes should be reported instead of the usual 10 minutes.

Question 3

How is wind speed reported?

Answer 3

Usually taken as the mean surface wind speed over the previous 10 minutes (Except when a marked discontinuity occurs), measured in Knots.

N.B.

• Rounded to the nearest Know between 01 and 99 Knots)
• If the speed is 100 Knots or more, the wind speed should be encoded as P99 e.g. 27070GP99KT

Question 4

What equipment is used to measure surface wind speed and direction.

Answer 4

Anemometer (Cup and vane or ultrasonic)

N.B.
- The standard height of an anemometer is 10m

Question 5

What is wind gust and how is it reported?

Answer 5

The maximum wind speed over the previous 10 minutes (or since the marked discontinuity). It is measured in Knots and only reported if it exceeds the mean wind speed by 10 knots or more.

Question 6

When are variations in wind direction reported?

Answer 6

When the total variation in wind direction over the previous 10 minutes (or since the marked discontinuity) is 60 degrees or more, but less than 180 degrees.

And

The average wind speed is greater than 3 knots

N.B.

• Variations are reported in clockwise order.
• If the first condition is met but the wind speed is 3 knots or less, the wind direction shall be reported as variable (VRB).
• If the total variation in wind direction over the previous 10 minutes (or since the marked discontinuity) is 180 degrees or more or where it not possible to report a mean direction e.g. when a thunderstorm passes over the aerodrome, The wind should be reported as variable (VRB) with no reference made to the 2 extremes in wind direction.

Question 7

How is wind reported when the wind speed is less than 1 Knot?

Answer 7

It is reported as calm - 00000KT.