Forecasting is impossible
Just in case anyone is interested, weather forecasting by computer modelling is impossible. The reason for this is that the equations which describe how atmospheric components interact are “Chaos” or “Sensitive Dependence on initial conditions” equations.
Very roughly, the way the modelling works is that you plug all your current weather data in to the Equations, do the sums and the answer is a new set of weather data. This data is used as input to the next iteration. This is repeated until you have rolled forward to the required point in time.
Implications of Chaos
The behaviour of Chaos equations varies depending on the input data. For some input values the equations will be stable. That means that if you run it multiple times with slightly different starting data, the results will be roughly the same. Running the equations with a different set of data will result in answers which significantly diverge.
The only way round this is for the input data to be 100% accurate for an infinite number of points on the Earth’s surface. This is impossible.
This means that if you run the model several times with different data and the answers are similar, you can be confident of you forecast. If the results differ, all you know is that you don’t know.
In conclusion
If you look synoptic charts in the run up to the period you want to forecast and they are dominated by a single weather system, you can believe the forecast. If there are lots of different systems interacting, then you may as well revert to seaweed.
Regards
Techno Freak