A white deposit of ice crystals on the windward side of objects, rime forms during foggy weather on cold days and creates a fragile beauty. It’s not to be confused with frost or glaze.
Rime is light, flaky and often thick. It is easily shattered. Examined up close, these white crystals on crabapples, twigs, grasses, wires or any object can be spectacular.
Fog is a cloud on the ground. It, too, is made up of tiny water droplets. These droplets change into rime when they hit cold objects. In our area, rime can be especially thick along rivers or open lakes. That is where steam fog is able to feed off warm waters. Rime is thicker on hilltop trees as opposed to valley areas. This happens because air is slightly chilled as it rises and expands.
Rime is not the same as an icy coating of glaze, which forms on trees and other objects when drizzle or rain falls. It is also not the same as white frost, aka hoarfrost, which is formed when water in its vaporous, invisible form clings to objects colder than the dew point. Rime is more dense and harder than frost.
White frost is the result of water vapor passing from a gas to a solid form. The solid ice crystals form on objects exposed to the air such as tree branches, plant stems, wires and poles. White frost forms when nights are clear and calm, and air next to the surface is relatively moist. The white frost, with its interlocking crystals, can transform a landscape of trees, shrubs, fences and utility wires into a splendid winter scene. The clear-blue morning sky and hoarfrost-covered countryside or cityscape really bring out the photographers and others who appreciate nature’s beauty.
Jim Gilbert’s observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.