Lines on the skew-T Saturation Mixing Ratio Lines

Saturation mixing ratio lines, also known as humidity mixing ratio lines, represent constant values of water vapor capacity—specifically, the number of grams of water required to saturate one kilogram of dry air at a particular temperature and pressure. On the skew-T diagram, the saturation mixing ratio (ws lines are the slightly-curved, dashed lines sloping from the lower left to upper right. They are labeled at the bottom of the diagram for a range of 0.1 to 40.0 grams per kilogram; i.e., in parts of water vapor per 1000 parts of dry air. Note that since the vapor capacity of air varies non-linearly with temperature, the labeling interval for ws lines is not uniform.