Although it looks a bit tacky, the Weather Tower by Belgian design studio lab[au] is a rather cool concept. The architects transformed Dexia Tower in Brussels into a light-based weather forecasting installation equipped with 72,000 LED lights across 6,000 windows. It's all controlled by a system that changes the color and geometric pattern to describe the next day's temperature, cloudiness, precipitation, and windiness.
A color-code corresponds to the upcoming day's temperature in comparison with the monthly average. The scale of color/temperatures range from violet (-6 or colder), blue (-4), cyan (-2), green (monthly average), to yellow (+2), orange (+4), and red (+6 or warmer).