The atmosphere is a chaotic system, and even negligible initial errors will give rise to gradual deviation of the forecast state from the true path, eventually resulting in chaos. This means that the weather has a predictability limit beyond which forecasts will lose all accuracy. Based on this, any single forecast is simply an estimate of the future state of the atmosphere within a stochastic framework, but provides no information regarding its reliability. Ensemble prediction offers one approach to generate probabilistic forecasts of the future state of the system based on a statistical sampling approach.