A new parameterization of single scattering properties has been developed for mid latitude cirrus clouds for application to weather prediction and global circulation models. Ice clouds are treated as a mixture of ice crystals with various habits. The bulk optical properties of ice crystals are parameterized as functions of the effective dimension ( De) of measured particle size distributions that are representative of mid latitude cirrus clouds. De is itself parameterized as a function of temperature and ice water content. The paper describes the results obtained with a stand-alone version of the radiation routine of the COSMO model and preliminary tests with the full forecast model in various meteorological situations characterized by extended high cirrus clouds over Europe.