Frost forming a broken glass pattern

[bbgunberrill]

During the winter, my windshield frosts a lot. But the frost forms in a broken glass pattern. It's only on the windshield that it does this. But my windshield is not cracked. Does anyone know the cause of this

[lannvouivre]

Perhaps a temperature difference caused by sun warming the inside of the car causes the ice to thaw just enough to move a little and crack?

[Derf]

Do you use additives in your windshield washer fluid, something like Rainx, park under a tree, or have a flock of birds nearby? Have spiderwebs mostly when the car is around freezing while the outside is much colder. As the water gets cold it nucleates around dirt and micro scratches on the windshield, the "cracks" you are seeing, are not from real cracks in the glass but likely the gunk that is stuck to your windshield. Took a clay bar to my "clean" glass, amazing what is lifted off. Reading your post got me to thinking, the frost on my window seems different after the clay bar treatment.

Link to an interesting video on ice formation. You can chill pure water below 20*F without it Freezing:
http://youtu.be/HatLN_C6V4k" onclick="window.open(this.href);return false;