Probabilistic forecasts of winter thunderstorms around Schiphol Airport using Model Output Statistics

The development and verification of a probabilistic forecast system for winter thunderstorms in the Netherlands is presented in this report. We have used Model Output Statistics (MOS) to develop the probabilistic forecast equations. The MOS system consists of 32 logistic regression equations for two forecast periods (0-6 hours and 6-12 hours), four 90x80 km2 regions around Schiphol Airport, and four 6-h time periods. For the predictand validated Surveillance et d’Alerte Foudre par Interférométrie Radioélectrique (SAFIR) total lightning data was used. The potential predictors were calculated from postprocessed output of two numerical weather prediction (NWP) models – i.e. the High-Resolution Limited-Area Model (HIRLAM) and the European Centre for Medium-Range Weather Forecasts (ECMWF) model - and from an ensemble of advected lightning and radar data (0-6 h projections only). The predictors that are selected most often are the HIRLAM Boyden Index, the ECMWF 6-h convective precipitation sum, the HIRLAM CAPE and two radar advection predictors. A verification was done using independent data from the winter season 2007-2008, from which it can be concluded that the MOS system is skilful. The forecast system runs at the Royal Netherlands Meteorological Institute (KNMI) on an experimental basis, with the primary objective to warn aircraft pilots for potential aircraft induced lightning (AIL) risk during winter.