Abstract
An objective and practical limit of predictability for NWP models is proposed. The time T0 is said to be the limit of predictability if model forecast beyond T0 has no extra skill over persisting the T0 forecast. The “skill” is measured here in terms of standard rms and anomaly correlation scores. For the NMC medium-range forecast model, T0 is found to be 5–6 days for 250, 500 and 1000 mb height forecasts for the period 5 May–25 July 1987. The T0 can also be interpreted as the time at which them is no longer skill in the prediction of the time derivative of the quantity under consideration.
