A simulation model of soil moisture and heat flux, FroST (frozen soil temperatures) was developed and applied to field data for the BOREAS northern and southern study areas (NSA, SSA). FroST is a modification of another soil physics model (Residue) <Bidlake et al., 1982> to which simple representations of snow dynamics and transpiration, canopy, and litter properties were added. Simulations were run for the old jack pine and black spruce sites at the SSA and NSA. Predicted results showed good fit to measured data for snow depth and soil temperature at various depths at the old jack pine sites for which measured data were available for 1994. The presence of ice through the soil profile was also predicted, indicating a longer and deeper frozen period in the NSA and the development of permafrost at the NSA black spruce site. The model was sensitive to initial conditions of soil moisture and temperature and soil profile characteristics. With the availability of these data, estimates of temperature and moisture flux in soils over time can be predicted. Because the model relies on soil characterization data and yet represents fundamental physical processes, it can be readily extended to new conditions or a wider range of sites. ¿ 1997 American Geophysical Union