The 'Snow Cover' tool uses a simple model to estimate snow cover statistics from climate data. When temperature falls below zero any precipitation is accumulated as snow. Temperatures above zero will diminish accumulated snow successively until it is gone completely. Simulation is done on a daily basis. If you supply the tool with monthly averages, temperatures will be interpolated using a spline and precipitation will be splitted into separate events. The latter is done with respect to the monthly mean temperature, i.e. the higher the temperature the more concentrated are precipitation events and vice versa.