Direction and speed of movement

(Section 2.7.5)

By convention, the direction of movement of a cloud is the direction from which the cloud moves. For example, if a cloud moves from south-west to north-east, the recorded direction of movement is “south-west”. The speed of a cloud is the speed of its horizontal movement.

An observation of the sky should report the direction and, whenever possible, the speed of movement of the clouds or their macroscopic elements. In most cases, this is also a good approximation of the direction and speed of the wind at cloud level. It is possible for the movement of a cloud as a whole to be very different from the movement of its macroscopic elements, particularly in the case of orographic clouds. When such a difference is observed, it should be reported.