Condensation forms when warm, humid air contacts a cold surface. Moisture is in the air all around us and warmer air can hold more moisture. As air cools, it contracts and its moisture condenses. When the temperature drops, the first place you will see any condensation is on the windows. Your windows are the coldest surfaces indoors. During colder months, indoor air is much warmer and holds more moisture than outdoor air, which is colder and dry. Warm, humid indoor air cools and contracts; as it contacts the cooler windows, the moisture condenses on the glass.