Practical estimation of long‐term daily Great Lakes evaporation requires one‐dimensional (depth) models of heat storage and mixing. Conceptual models are preferable to physical models for small‐computer simulations that are multiple, continuous, and long. This paper describes a new conceptual superposition model of heat storage to extend an existing evaporation model along the lake depth. The resulting daily model is recalibrated to remotely sensed surface water temperatures and is used to illustrate anew seasonal heating and cooling cycles, heat‐temperature hysteresis, water column turnovers, and mixed‐layer developments. It is used as well to compare the vertical distribution of temperatures with independent bathythermograph data. The time occurrence structure of evaporation on the Great Lakes is investigated, and the effects of summertime initial conditions on subsequent wintertime behavior of evaporation are simulated. Impacts of perceived large‐lake thermodynamic behavior are analyzed, and suggestions are made for furth