If you look at Snow depth forecast by the default model (ECMWF), it is obviously wrong at Lago di Resia level which is surrounded by 3000m mountain tops. This model has a resolution of 9km and a coarse topography model. It is like using a camera with a low resolution: you would not get precise details of photos.
Try to use the ICON-D2 with a 2km resolution. It forecasts only 0,5cm at lake level, which is closer to the reality !