Published: 2009-01-04 10:35:52
Updated: 2009-01-04 10:35:52
Posted January 4, 2009
MIKE MOSS SAYS: Lewis, What you described does happen from time to time here in our area when the vertical profile of temperature and humidity vary in such a way as to support changing precipitation types. If the air is sufficiently cold over a sufficient depth to produce a layer of snow on the ground, and later the air aloft warms up enough to produce rain instead, but a subfreezing layer of air near the surface cools the raindrops below 32 degrees before they reach the surface, they may freeze upon contact into a glaze of clear ice atop the snow. This is the process we call "freezing rain," which can occur under the right circumstances regardless of the presence or absence of snow on the ground. In addition, it is possible for warmer, non-freezing rain to fall on the snow and begin to melt it, then have the temperature turn colder and cause the entire slushy mixture to freeze into hardened ice.
Since it isn't all that rare to have some of these transitions from one precipitation type to another in our wintry weather episodes, sometimes in the end you can slice down through the accumulated precipitation and clearly see layers of powdery snow, pellets of sleet, clear ice, and occasionally hardened slush stacked one atop the other, in varying orders depending on how the winter storm evolved over time.