This paper presents the effect of atmosphere attenuation during serve weather conditions such as clear, fog and rain weathers. The usage of FSO is still rare in all the world due to environmental factors but it can be use in EGYPT because it has a good weather most of days and high visibility. FSO links are depends on the weather conditions and attenuation factor like temperature, height, visibility and the operating wavelength. In this paper, the attenuation of different wavelengths of the FSO links has been analyzed.The main aim is to examine the vulnerability of FSO against severe weather conditions. Models have been designed to simulate most of the weather conditions in Egypt by using MATLAB software and Application designer interface. Also, optimization has been done for the parameters to improve the FSO link capability to detect the weak signal at the maximum range.