We provide a forum for European collaboration on modeling atmospheric discharges, specifically Transient Luminous Events and High Energy Emissions from Thunderstorms like TGFs, as well as the impact of particle showers created by high energy cosmic particles. We will discuss physical concepts and results as well as input data, numerical methods, approximations and model reduction and possibilities of sharing code. The workshop is supported by the ESF research networking program Thunderstorm Effects on the Atmosphere-Ionosphere System (TEA-IS).