Strange Windshield Frost

April 13, 2017

April 2017 Viewers' Choice
: Ralph Winrich
Summary Authors: Ralph Winrich; Jim Foster

The photo above may look like an image from a flyby of Pluto, but instead is a strange diamond or cubic-shaped frost pattern on my car windshield, as observed at my home near Stoughton, Wisconsin, on the morning of February 27, 2017. It's a standard windshield, made of laminated glass like nearly all windshields today, and as far as I could tell, it wasn't pitted or defective in any way.

The temperature at the time the image was taken was 26 F (-3.2 C). The previous day's maximum at nearby Stoughton, was 41 F (5 C) and the minimum on the 27th was 21 F (-6 C). The sky was clear and the winds very light, from the south at less than 5 mph (8 km/h). A similar pattern was photographed on a windshield in Birch Bay, Washington (November 22, 2013), with temperature, wind and sky conditions nearly the same as for the Wisconsin case.

Frost crystals are affected by surface imperfections (scratches, cracks, concavity, etc.) as well as the temperature and cleanliness of the glass, the presence of moisture and even the presence of chemical residues on the glass surface. For instance, pollen or dust particles may act as nucleation points for crystalline formation. Ice crystals can grow quickly and take on bizarre patterns when both atmospheric and glass conditions are favorable. How these crystals formed as they did is hard to fathom, but perhaps the windshield being warmed in the previous afternoon's sunshine together with sufficient water vapor near the ground (during the overnight hours) and chemical residues on the glass surface all contributed to this strange pattern.

Photo Details: Nikon D 80 camera; lens 35 mm; ISO 800. Top - Close up of windshield showing strange frost pattern. Bottom - Full image showing entire windshield.