Qualitative use of the EPS If forecasts starting from these perturbed analyses agree more or less with the forecast from the non-perturbed analysis (the EPS Control forecast), then the atmosphere can be considered to be in a predictable state and any unknown analysis errors would not have a significant impact. In such a case, it would be possible to issue a categorical forecast with great certainty. If, on the other hand, the perturbed forecasts deviate significantly from the Control forecast and from each other, it can be concluded that the atmosphere is in a rather unpredictable state. In this case, it would not be possible to issue a categorical forecast with great certainty. However, the way in which the perturbed forecasts differ from each other may provide valuable indications of which weather patterns are likely to develop or, often equally importantly, not develop.