The exchange of energy between the snowpack and its environment ultimately determines the rate of snowpack water losses due to melting and evaporation/sublimation. Energy exchange primarily occurs at the snowpack surface through exchange of shortwave and longwave radiation and turbulent or convective transfer of latent heat due to vapor exchange and sensible heat due to differences in temperature between the air and snow. Relatively small amounts of energy can also be added due to warm rainfall on the snowpack surface and soil heat conduction to the snowpack base. Changes in snowpack temperature and meltwater content also constitute a form of internal energy exchange. Melting usually represents the major pathway for dissipation of excess energy when the snowpack ripens and becomes isothermal at 0'C (see Chapter 3).