An aerological diagram with the x, y coordinates temperature (T) and Entropy (phi). The lines of equal entropy are also the dry adiabatics. It is used for plotting temperature and humidity at specified pressure levels. Stability can be worked out by comparing the plotted lapse rate with the lines representing dry and wet adiabatics.

See thermodynamic diagram.

A tephigram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. The name evolved from the original name "T-\phi-gram" to describe the axes of temperature (T) and entropy (\phi) used to create the plot. Usually, temperature and dew point data from radiosondes are plotted on these diagrams to allow calculations of convective stability or Convective Available Potential Energy.