So why do planes fly so high? Because planes fly higher than the clouds to avoid harsh weather. The usual weather we know of, rain, snow and thunderstorms, all occurs in the troposphere, which is at the average of 36,000 feet, the closest atmosphere layer to the Earth surface. This is where all the clouds are, essentially the thickest layer of the air concentrated with water vapor. Planes fly above the layer at 37,000 feet, so we avoid facing the danger of weather. When your planes are having turbulences, it is often caused by the airplane slicing through this troposphere layer, which rich is water vapor and ice. In addition, the clouds and water droplets might reduce the visibility of the pilots. Hence, the flight at the high altitude is some much safer.