Great Lakes hydrologic research requires the use of continuous-simulation daily ice cover models over long time periods in the absence of field observations. They must be physically based, rather than statistically based, for use under conditions different than those under which they were derived. But they also must match existing conditions for which data exist. A review discloses that existing ice dynamics models do not meet all of these criteria; a new one that does is based here on a prismatic ice pack heat balance, ice growth and temperature constraints, and thermodynamic flux terms from companion water heat balance and storage equations. The prismatic ice model is a good first step to understanding complex geometries and is supportable through the use of lake-averaged energy fluxes. The ice model is integrated into an existing lake thermodynamics and one-dimensional heat storage model, and the resulting combination is calibrated for Laurentian Great Lakes applications. Simulation experiments are used to analyze the model's strengths and limitations and to explore its relevance. Comparisons between model output and existing data allow consideration of the ice climatology of the Great Lakes; the climatology description is extended through use of the new model. Promising potential model extensions include spatial extension, additional parameterizations for wind-ice movement, snow, and albedo, and inclusions of remotely sensed data.