In Chapter 5 of this book, it is shown that the formation of ice on the surface of a lake (‘ice-on’) and its thawing and ultimate disappearance (‘ice-off’) are complex phenomena governed by mechanisms that involve many interacting meteorological (and some non-meteorological) forcing factors. Linking ice phenology – the timing of ice-on and ice-off – to climatic forcing might therefore be expected to be a difficult task. This task, however, is simplified considerably by the fact that air temperature is the dominant variable driving ice phenology (Williams, 1971; Ruosteenoja, 1986; Vavrus et al., 1996; Williams and Stefan, 2006), and is also correlated to some extent with other relevant meteorological driving variables such as solar radiation, relative humidity and snowfall.