Sounding Data » Temperature/Dewpoint Description

To create temperature and dewpoint curves on a skew-T, first plot the temperature and dewpoint at each individual pressure level in the sounding. All mandatory and significant level sounding data should be plotted. Then, connect the temperature points with straight lines between successive pressure levels, often using red. Similarly, connect the dewpoints with straight lines, often using green or blue.
The dewpoint is the temperature to which a parcel of air at a constant pressure becomes saturated without any addition of water vapor. For instance, at ground level this is the temperature at which dew would be expected to form.