Revisiting the Question of Atmospheric Predictability

This study seeks to demystify the claim that the ‘atmospheric chaos’ imposes a two-week limit on reliable weather forecasts. ‘Deterministic chaos’ indeed occurs due to the use of nonlinear numerical models for these forecasts. This ‘deterministic chaos’ does impose time limits on valid predictions, but it also facilitates, through the ensemble forecasting technique, the use of interesting statistical indicators that define regions and the duration these predictions are more or less reliable. Recently published articles show that the ‘uncertainties’ in the initial conditions are an inherent difficulty in meteorological observations and have nothing to do with the atmospheric behavior. These studies demonstrate two important aspects regarding ‘uncertainties’ in data used to initialize models. First, to achieve improvements in numerical weather forecasts, these ‘uncertainties’ must be skillfully introduced in the large scale and not in the small scale. Secondly, the numerical models must include equations or parameterizations that reproduce nature’s ways that let different scales ‘interact’, that is, the models should reproduce how the energy of different atmospheric modes ‘travels’.