To design a weather app, I would focus on a user-centric approach, prioritizing clarity, accuracy, and ease of use. Key features would include current weather conditions, hourly and daily forecasts, severe weather alerts, and customizable location settings. For advanced functionality, I'd consider integrating features like radar maps, air quality index, and historical weather data. The design would emphasize a clean, intuitive interface with visually appealing data representation. Scalability and performance would be critical, ensuring the app can handle large amounts of data and provide real-time updates efficiently. Error handling and offline capabilities would also be important considerations.