The model is based on the closure of spectral turbulent equations using a semiempirical hypothesis for the spectral characteristics of turbulence. Expressions are obtained for the mean values of coefficients of turbulent viscosity and heat conduction, evaluated over one period of the internal gravity wave (IGW). Evaluations are made of typical effective turbulent Prandtl numbers for the inhomogeneous turbulence which is produced by breaking saturated and nonsaturated IGW in the middle and upper atmosphere. -from Authors