Windrose

http://www.climate.washington.edu/climate.html

 
     Windrose maps represent the direction in vector form of the wind at certain speeds. The frequency of the winds at that speed and direction can be determined based on the length of the vector. This example shows the data collected in Seattle, Washington where the most common wind direction appears to be almost due south. The colors in the vector indicate wind speeds in knots, and the legend is also shown to depict the colors.