
A measure of the accuracy of a forecast compared to a reference, such as climatology or persistence.Forecast skill is a way to score how much better a prediction is than a simple, cheap baseline. The baseline is often 'climatology' — just predicting the long-term average weather for that date — or 'persistence' — predicting that tomorrow will be like today. A forecast with high skill beats these naive guesses by a meaningful margin; a forecast with zero skill is no better than the baseline, and negative skill means it is worse.
Skill is usually expressed as a ratio or percentage comparing the forecast's error to the baseline's error. For example, the Brier skill score for probabilities or the mean squared error skill score for continuous values. If the forecast error is half the baseline error, the skill is 50%. This normalizes accuracy so you can compare forecasts across different places, seasons, or variables, where raw error alone would be misleading.
Meteorologists use skill scores to decide whether a new weather model is worth adopting, and climate scientists use them to validate seasonal predictions against a simple 'average year' forecast.
A forecast can be perfectly calibrated — meaning it is correct on average — yet have zero skill if it never beats the climatological baseline.











