Hoarfrost coats every surface - branches, fences, grass blades - in intricate white ice crystals. It forms when temperatures are below freezing, humidity is high, and wind is light enough that the delicate crystals aren't blown away. Colder temperatures (below -5 degrees C) produce thicker, more dramatic frosting.
Inverza checks temperature, humidity, and wind speed, weighting colder temperatures and higher humidity more heavily. The condition targets the early morning hours before the sun melts the frost.