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.