Accurate wind measurements hard to obtain

The graphic below illustrates one of the many ways forecasters measure wind speed and direction. Both the wind vane and the cup anemometer are mounted on vertical poles that can rotate. In this example, electrical switches mounted on both the rotating disc and the non-moving cylinder around the rotating disc are used to determine both wind speed and direction. Wind measurements have always been one of the more difficult observations for forecasters to take. One of the main reasons is how quickly wind speed and direction can vary over short distances, especially in cities and other areas with a lot of obstructions. Buildings and other obstructions create eddies which make it difficult to determine the true direction and speed of the prevailing wind. Wind directions are always reported as the direction winds are coming from. In other words, a northerly wind pushes air from the north to the south.

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