Icy designs on window

When temperatures dip down to 0°F (-18°C), we get interesting patterns of frozen crystals on the single pane glass of the storm door. These doors are designed to form a barrier between the cold outside and the main door.

It has done its job, but it also gets exposed to the moisture from inside so when we open the door to let our dog go outside, it frosts up. At night the lights form beautiful patterns.