Chris Plastow
Without getting too complicated.... There is this thing called Relative Humidity (RH) . Air can hold more water at high temperatures than low and the humidity is measured relative to the temperature . So, one cunic metre can hold , let's say , 50ml of water at 25C but at 13C it can only hold 12ml . As the temperature drops from 25c the water must be lost , outside it's called rain, snow etc. inside it's called condensation . Your windows are cold and so the moisture is lost to the glass , being the lowest temperature surface .
