Since the advent of rawinsonde observations, thermodynamic diagrams have been used by meteorologists to analyze sounding data in the course of preparing their weather forecasts. This module comprehensively examines the use of the tephigram, widely used for over 60 years by meteorologists in the United Kingdom, Canada, and other countries throughout the world particularly in Europe and Africa. It explores thermodynamic properties, convective parameters, stability assessment, and several forecast applications. The module is designed for both instruction and reference. It also comes with an interactive Web-based tephigram that calculates several common forecast parameters.