Adiabatic compression occurs when air sinking down the hill in Duluth experiences increasing pressure from the air above. The increased pressure warms the air. Since the spread between the temperature and dew point increases, the air also dries. When snow is falling, the drying of the air erodes some of the snow due to sublimation. Sublimation is the process by which water changes phase from ice to water vapor. If the temperature at the top of the hill is around 32 degrees Fahrenheit (^oF), the air will warm above freezing as it sinks. The warmer temperatures melt some of the snow and retard accumulation. Some warming is balanced by the sublimation and melting since both processes remove heat from the air. When conditions are drier, air can warm 4 degrees or even a little more. Heavier snow means increased sublimation or melting and greater odds that snow will accumulate at the bottom of the hill.