In this study, the performance of different wind turbines located in 2 mountainous regions in Switzerland, the Lukmanier Pass and the Gotthard Pass, are assessed with respect to different parameters. For both sites, a thorough wind assessment is firstly done, showing that the wind generally follows the main axes of the passes. It is notably found that turbulence intensity is different depending on the wind direction, and is also strongly affected by terrain for winds close to the ground. The impacts of air density, varying with altitude notably, on wind turbine efficiency are analysed first. These are clear, as the output power of a wind turbine is directly proportional to the air density. Then, the effects of turbulence intensity are examined. It is found that a high turbulence intensity allows for a better wind turbine performance at low wind speed. On the contrary, a low turbulence intensity at high wind speeds leads to a better performance. OpenFAST is used to verify these results. Temperature is the next variable studied, and it is shown that a lower temperature generally leads to a higher power output. Finally, the presence of snow at the wind turbine site and its impacts on the wind turbine performance are also analysed. It is found that the wind turbines generally perform best if a snow cover is present. This layer of snow moreover allows for a generally higher wind speed, potentially leading to a higher energy production. For the Gotthard Pass, the effects of these parameters are different for each wind turbine, highlighting the complexity of assessing the wind potential when planning a wind energy installation in a precise area. For the Lukmanier Pass, further developments and annual energy production are discussed.