However, global mean precipitation is controlled not by the availability of water vapour, but by a balance between the latent heat of condensation and radiative cooling in the troposphere. (ipcc.ch)
When it reaches a level high enough to cool it to it's «dew point» the water vapour condenses out in the form of clouds and rainfall and the Latent Heat of Condensation is released into the upper part of the atmosphere to accelerate the escape of radiant energy to space. (newclimatemodel.com)