Dear Tom,
What is the difference between rime ice and hoarfrost?
John Toles
Dear John,
A casual observer will notice little difference between the two, but the meteorological dissimilarities are considerable.
Hoarfrost is the technical name for ordinary frost, the fuzzy layer of ice crystals that forms on grass and objects, usually near the ground, when airborne water vapor condenses (technically, sublimes) at subfreezing temperatures directly onto their surfaces without passing through the liquid phase.
Rime ice forms in below-freezing air when supercooled fog droplets strike and immediately freeze on exposed objects like grass, trees, buildings, etc. The result is a milky white, granular deposit of ice that is spectacularly beautiful when it transforms a landscape of trees into a white wilderness.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
