Optical wireless communication has the tremendous potential to support high data rate demanding future communication applications. However, the weather influenced reduced availability has been the hindrance for widespread growth of optical wireless communication technology. Among different attenuating factors, fog is the most critical that causes significant attenuation for non negligible time. In this paper, the best fit distribution for measured dense fog visibility has been found. The availability estimation has been performed using best fit measured visibility distribution. Monte Carlo simulation has been used to for availability estimation.