A tool for assessing the quality of the Mediterranean cyclone forecast: a numerical index

Abstract. Cyclones affecting the Mediterranean region, sometimes related to severe weather events, are often not well represented enough in numerical model predictions.

Assessing the quality of the forecast of these cyclonic structures would be a significant advance in better knowing the goodness of the weather forecast in this region, and particularly the quality of predictions of high impact phenomena.

In order to estimate the cyclone forecast uncertainty in operational models, in this work we compare two cyclone databases for the period 2006–2007: one from the operational analyses of the T799 ECMWF deterministic model; and the other from the forecasts provided by the same model in three ranges, H+12, H+24, and H+48. The skill of the model to detect cyclones and its accuracy in describing their features are assessed.

An index is presented as an indicator of the quality of the prediction, derived from the frequency distribution of errors in the prediction of four characteristics of the cyclone: position, central pressure value, geostrophic circulation, and domain. Some sub-indexes are derived to verify each of the variables separately in order to analyse the most frequent sources of error. Other sub-indexes are also defined to indicate possible biases in the numerical prediction model.