The aim is to develop a physically based theory for heat and mass fluxes (diffusive and convective) in snow. The absence of a reliable mathematical model is a crucial problem in understanding snow cover evolution and snow crystal metamorphism. Snow cover models are important for hydrology and climate models, since the difference between the heat fluxes beneath and above a snow cover greatly affect the energy balance of soil and of the atmospheric boundary layer. The heat and mass transfer in snow determine the activity of snow recrystallization (the time evolution of snow micro-structure described by snow crystals' shape and their relative positioning). The latter is of great importance for snow avalanches forecast, because different micro-structure corresponds to different mechanical properties. In addition, shape and dimensions of snow crystals forming snow layers in natural snow cover are responsible for the optical properties of snow cover, such as snow albedo and microwave emissivity, the first one being one of the main parameters for the bottom boundary condition in atmospheric models, while the second one, affected by temperature, is the parameter observed by remote sensing techniques. Despite reported success of a number of snow cover models (SNOWTERM, CROCUS, SNOWPACK) in prediction of some of snow cover properties, the accuracy of the modeling results is known to be limited by a number of assumptions: local thermophysical steady state, saturation of the water vapor in the pore space of snow, equality of temperatures of the pore air and of the ice matrix. As the result of these assumptions, a model validated in certain landscape/climate conditions requires new adjustment coefficients for reasonable result in any other geographical region. The only way to avoid that is developing of a more accurate physical/mathematical description of the heat and mass transfer processes, and this is not an easy task: The heat transfer in snow is not purely conductive mechanism. The flux related to the phase transitions at the ice matrix surface release/gain of the latent heat was estimated to be 15-30% (in dependence on the internal geometry of snow and the environmental conditions) addition to the effective heat conductivity of snow. Evidently, the heat transfer in such a complex system as snow cannot be accurately described by a mechanical addition of this term to the combination of the presently used in published models Fourier and Fick's Laws. The aim of the proposed project is to analyze the interplay between all the known heat transfer processes in snow theoretically and to find a proper way for mathematical description of the simultaneous heat and mass transfer. Finally, a mathematical model of the heat and mass fluxes without fitting parameters, but instead based on independently measured physically-meaningful coefficients will be developed. The model will be verified by data Dr. Sokratov has collected from the cold laboratories of the Swiss Federal Institute of Snow and Avalanches Research (both the participants are related to) and of the Laboratory of Modeling of the Cryospheric Processes of the Faculty of Geography, Moscow State University.