Air is a mixture of many gasses including nitrogen, oxygen, carbon dioxide, ozone, argon and water vapor just to name a few. While oxygen and nitrogen generally exist in the same proportion regardless of altitude or location over the earth, the amount of water vapor in this mixture varies greatly with location and altitude. Knowing the relative humidity doesn’t specifically identify exactly how much water vapor is in the air, but it does tell you if the air is saturated or how close the air is to becoming saturated. High values of relative humidity can lead to the formation of clouds and precipitation which can lower the visibility or lead to structural icing given the right range of temperatures. In this workshop we will explore how to calculate the relative humidity on a Skew-T log (p) diagram.