This Web-based learning module is the second title in a series of modules about the use of diagnostic tools to evaluate icing type and severity. Marcia Politovich of the NCAR Research Applications Program (RAP) is the principle subject matter expert. The module teaches how to assess surface observations, upper-air charts, and pilot reports (PIREPs) in order to diagnose the aviation icing environment. Topics include strengths, weaknesses, and appropriate uses of these data, data assessment methods, interpretation and evaluation of PIREPs, and a bottom-up procedure for integrated icing diagnosis at a particular location. This module includes numerous practice exercises allowing learners to improve their skills in icing assessment using these basic observational tools.