Operational flexibility is an integral part of the design of power systems with a high share of renewable energy sources. Resilience against severe weather is also becoming an important concern. In this paper, we propose a comprehensive framework for power systems planning which considers both flexibility and resilience against extreme weather events. A set of piece-wise linear models are developed to calculate the impact of extreme heat waves and drought events on the performance of the power generation units and on the system load. We analyze the results obtained on a case study under real future climate projections from the Coupled Model Intercomparison Project phase 5 and compare them to those from conventional planning methods.