Complex sentence: Variables used in models include properties of the ice such as thickness, density, temperature, c-axis fabric, impurity loading, though'ice front normal spreading stress', is likely the most important variable, however it is usually not measured.
Split into simpler sentences: Variables used in models include properties of the ice such as thickness, density, temperature, c-axis fabric, and impurity loading. The ice front normal spreading stress, is likely the most important variable, although it is usually not measured.