Precipitation is formed and changes between a solid, liquid and gas because of three factors: temperature, pressure and humidity. Humidity is an important effect on the formation of snow because humidity is the measure of the amount of water air can hold. The amount of water the air can hold is dependent on the temperature. The higher the temperature, the move water the air molecules can bond with. When the humidity is high then there is enough water in the air to make precipitation. When the humidity is high there is a large amount of water in the air, if the temperature drops then the pressure also decreases. A drop in temperature squeezes the air molecules close together and squeezes out the water which makes rain or snow. Humanity affects snow in an interesting way because according to the temperature and pressure different snow shapes are formed. At low temperatures dendrites and sector plates are formed and at higher temperatures hollow columns, needles and thin plates are formed. Humidity not only affects snow formation but it also affects how and when snow melts. When the air is humid it is easier to transfer heat to ice from the air. Since the pressure is constant when snow is on the ground, the temperature of melting ice is at a fixed level according to Gibbs phase rule. If the air is more humid then more heat is being transferred to ice from the air and the snow melts. Humidity is affected by temperature and pressure and according to these three factors precipitation can be altered into different phases. In relation to snow, when the humidity is high pressure is high and temperature is low snow is formed. When the humidity is high, pressure is constant and temperature is high the snow melts.