A problem we have in tracking clouds is that we do not know the path they take (there are no roads in the sky for us to follow!). In fact, if we can determine the path they take we can determine the wind direction. Watch the image of the car on the previous page and imagine that you did not have the roadway to help determine the car's path. So without a roadway, how can we determine the path? A good way to determine the path of the car is to track two images of the car that are close in time.

The same thinking applies to clouds. Because we do not have a road to help us determine the cloud's path, we view two images of a cloud that are close in time. Long time intervals are not good for tracking clouds that are changing rapidly. Short time intervals (1 to 15 minutes) are best when clouds are moving quickly.

In tracking clouds we have additional problems besides not knowing the actual path. View the following animation of a cloud and come up with a list of additional problems we might encounter when tracking clouds to determine wind speed and direction.