Heat Deficits

The heat deficit is defined as the amount of heat that must be added to return the snow pack from below 0 ºC to an isothermal state (0 °C) (Anderson 1973; Anderson 1976; Melloh 1999). The equations to calculate the heat deficit within this report are based on the National Weather Service River Forecasting System (NWSRFS) SNOW-17 model (Anderson 1973). There are two types of heat defi-cit, one caused by temperature and one caused by precipitation. It is important to include the heat deficit because melt and rain continue to refreeze within the snow cover until the heat deficit reaches zero (Melloh 1999). The heat deficit described below is in units of mm of SWE, making it easily incorporated into most snow melt routines by simply reducing the amount of melt (in mm of SWE) calculated in the melt routine by the heat deficit.