GRAND RAPIDS – I’ll bet that’s a term most people haven’t heard before…hoar frost! With the clear skies and very cold temps Friday night into Saturday morning, we saw some pretty thick frost across the area. That may not be unusual in and of itself, but hoar frost isn’t something we see all the time.
Hoar frost is easy to understand. We all know there’s water vapor everywhere. It’s inside and outside all the time. Hoar frost occurs when water vapor outside comes in contact with something below freezing (like vegetation) and freezes instantly on contact. Another definition is a direct deposit of ice crystals on objects in air and is formed by direct condensation of water vapor to ice. The technical meteorological term is called deposition and is considered a phase change. It is the opposite of sublimation.
Without trying to get too technical, remember every time there is a phase change of water, energy is either taken from or released into the atmosphere…depending on what that change is. In the case of deposition, heat is being released into the atmosphere. Click here for an easy to understand diagram. Hoar frost tends to occur during the winter on clear, cold nights where everything outside is well below freezing. Again, this allows the invisible water vapor floating in the air to change phases (or go from a gas to a solid) and condense on the frozen surface immediately as ice.
Sometimes hoar frost can be so thick people mistake it for snow. The attached photo was submitted to our FOX 17 Facebook page by Peg Gornick. It’s clear to see why some would mistake this for snow as widespread hoar frost can turn an average cold winter morning into a beautiful winter wonderland.