Ever been curious how those weather forecasts you get on your phone and on the news are created? Welcome to the wonderful world of chemical transport models (CTMs), the largely open source software behind modern weather and air-quality prediction. Modeling agencies and numerous state and local environmental offices rely on systems like the Weather Research and Forecasting model with Chemistry (WRF-Chem) and the Unified Forecast System (UFS) to simulate how gases, particles, and meteorological conditions evolve in the atmosphere. UFS provides large-scale, global weather analyses and forecasts that supply essential boundary and initial conditions, while WRF-Chem couples weather dynamics with detailed chemical processes to resolve regional air quality with high spatial precision. Together, these models allow weather agencies, and now you, to translate complex atmospheric science into the clear, timely information that allows us to anticipate rain, model winds, or predict pollution events using our trusty Linux machines. Come learn how WRF-Chem works: how to customize it to run over your area, the kinds of openly available inputs it uses to establish initial and boundary conditions, and examples of how the generated predictions compare to real-world outcomes.