A new model for turbulent flows with stable stratification is presented. This model belongs in the class of the quasi-Gaussian closures; its parameters are calculated based upon a self-consistent recursive procedure of small-scale modes elimination starting at the Kolmogorov scale kd. The model includes both vertical and horizontal eddy viscosities and diffusivities thus explicitly recognizing the anisotropy induced by stable stratification. There are significant differences in the behavior of these turbulent exchange coefficients with increasing stratification. Generally, the vertical coefficients are suppressed while their horizontal counterparts are enhanced. The model accounts for the combined effect of turbulence and internal waves on the exchange coefficients. A dispersion relation for internal waves in the presence of turbulence is derived. A threshold criterion for the wave generation in the presence of turbulent scrambling is obtained. The new model can be used to derive subgrid-scale parameterizations for LES and eddy viscosities and diffusivities for RANS models. The latter approach is used to develop a new K -? model which is tested in simulations of the atmospheric stable boundary layer (SBL) over sea ice. The new model performs well in both moderately and strongly stratified SBLs.