Midlatitude weather systems, such as extratropical cyclones, fronts, and their embedded thunderstorms are vital for the day-to-day variability of precipitation and winds. We have used a number of objective techniques to identify these weather system types, in order to understand the links between the weather systems and hazards in observations. We have then used this understanding to evaluate climate models and to better understand the response of the weather systems and the high impact hazards to a warmer climate.