We present a numerical formulation to compute optical parameters in a turbulent air flow. The
basic numerical formulation is a large eddy simulation (LES) of the incompressible Navier-Stokes
equations, which are approximated using a finite element method. From the time evolution of the
flow parameters we describe how to compute statistics of the flow variables and, from them, the
parameters that determine the quality of the visibility. The methodology is applied to estimate the
optical quality around telescope enclosures.