A two-dimensional finite difference diffusion model was developed to analyze the effects of a propagating ice front on the continuous wave intensity transmission across a tissue sample. The calculated diffusion model transmissions for a transilluminating emitter/detector fiber configuration were compared to experimentally obtained transmissions for consecutive ice front positions within the tissue sample. The diffusion model was able to predict the transmission behavior for this fiber configuration given the absorption and scattering coefficients of the frozen and unfrozen tissue. Calibration algorithms for similar fiber probe placements based on this model may eventually be used with real-time transmission measurements to allow visible light monitoring of ice front position in tissue. This demonstration has potentially important medical applications in cryopreservation (freezing of biological materials for preservation) and cryosurgery (destruction of tissue by freezing).