Weather prediction is based on various pieces of technology and what we know about physics and trends. We don't know nearly as much as we could know which is why the weatherman is often wrong. All we can do is see what's happening now and assume it will continue along that path, we can also see it begin to change, but we can't always explain why and we often miss the signs.
First data is collected from trained observations, temperature, wind speed and direction, humidity, and so on. Various devices are used to collect all this data; weather balloons are used to find the measurements for the above list higher in the sky. We now have weather satellites to give us a bird's eye view. These measurements are taken at various times to see how they are changing.
A model is created on a computer that uses what we know about physics and fluid dynamics and the measurements taken over time to solve complicated equations. The air around us is much like water in how the physics of it works, but it is not nearly as dense as water, nor can we easily see wind and air pressure. The math involved due to this is arduous.
The results of the super computer are then presented to the public in an understandable format. We hear a high-pressure system is moving from the north instead of the math that would explain that to a trained professional.
Shifts in weather often go undetected. Some types of weather are completely unpredictable, such as tornados. We do not understand enough about physics and fluid dynamics to be able to predict a tornado, yet.
www.theweatherchannel.ca
http://asp.usatoday.com/weather/weatherfront.aspx
