Measuring weather

Surface observations - wind

Whenever there is a difference in pressure across some horizontal distance (across land) or a difference vertically (between air near the ground and that high in the sky), the air must move to equalize the difference. When the air moves, you get wind. Air moves in three dimensions, but when observing the wind, meteorologists often separate the motion into the horizontal wind and the vertical wind.

For the horizontal wind, meteorologists like to know the direction the wind is coming from and the speed at which the air is moving. Direction is reported with a meteorological angle, for example, a wind from the North is called a "northerly" wind and is denoted as N or 0 degrees. Similarily, a wind from the south-southeast is denoted as SSE or 157.5 degrees.

Wind observations are also frequently represented in a graphical form called a wind barb. Think of the wind barb as an arrow that has a head pointing in the direction of the wind. The half line, full line, and triangular flag barbs on the arrow denote the approximate wind speed within 5 knots (just over 5 mph). A set of concentric circles without an arrow shaft represents calm conditions.

 

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