Analytic methods are useful for lake ice climatology investigations that account for ice phenology, thickness, and extent. Ice climatology depends on the local climate and lake characteristics, which can be compressed into a few forcing factors for analytic modelling. The internal factors are lake depth, size, and water quality, while the external factors are solar radiation, air–lake interaction, and heat flux from bottom sediment. A two-layer temperature structure with a sharp thermocline in-between is employed for the water body and a non-inert conduction law for the ice cover. A thermal equilibrium approach results in temperature and ice thickness solutions, and a time scale analysis provides the applicability of the equilibrium method for lake ice climatology. A non-steady solution is needed for ice melting.