The survival and beta models forecasting ice cover around the Apostle Island National Lakeshore use Lake Superior surface water temperature data collected from the Great Lakes Environmental Research Laboratory (GLERL). GLERL hosts Lake Superior surface water temperature data pre-1995 from the Large Lake Thermodynamics Model (LLTM) and post-1995 from the Great Lakes Surface Environmental Analysis (GLSEA). The pre-1995 data is currently being moved and is unavailable from GLERL, and therefore, the (entire) surface water temperature record used by the models is hosted here. Please see the methods for direct data access links.
The LLTM, the source of the pre-1995 data, is described in Croley II, T. E., & Assel, R. A. (1994). A one-dimensional ice thermodynamics model for the Laurentian Great Lakes. Water Resources Research, 30(3), 625–639. Documentation on GLSEA can be found on their website.