A weather vane is one of the oldest weather prediction tools still in use today. Using shapes such as a rooster, ship or arrow, weather vanes were originally designed to rotate freely on an axis to display the direction of the wind. Prior to the development of modern meteorology, information such as a change in the wind was used in conjunction with other easily obtainable data to derive a short-term weather forecast.
Choose an appropriate site for your weather vane. In order for a weather vane to function properly, it must be placed high above the ground and well away from any large items that may obstruct or temporarily influence the direction of the wind. In general, weather vanes are placed at the highest point of a structure in a clear and easily visible location.
Use a compass to derive the four main directions of the wind (North, South, East and West). Most weather vanes are designed with stationary directional indicators. By using the compass when installing the weather vane, you can ensure that each marker is set in the proper direction. Make a notation of each direction so you can reference it later.
Observe the weather vane during the approach of inclement weather and record any movements in your notebook. Also, make note of the visible environment--the color of the sky, the size and shape of the clouds, the time of day, temperature etc. Remember, the weather vane points in the opposite direction of the way the wind is blowing. For example, if the vane is pointing south, you're experiencing a northern wind.
Review your log every few months and take notice of any patterns that become evident. Over time, you will begin to observe regional trends which will allow you to predict the weather in your area with a fair amount of accuracy.