WINTER PRECIPITATION

A wide variety of precipitation from snow and rain, to sleet and freezing rain occur in the winter months. Temperatures at the ground and up to about 5 thousand feet in the atmosphere determine precipitation type. Sharply varying temperatures over just a few miles, both aloft and near the ground, can produce quick changes in the type and amount of precipitation.

In the diagram below, snow is produced when temperatures are uniformly cold both aloft and at the ground. The snow does not melt as it falls, and temperatures at or below 32 degrees near the ground allows it to accumulate.

However, sleet is formed when temperatures at or slightly above freezing aloft produce rain that freezes to ice pellets, as it falls into a cold layer of air. Sleet usually bounces when hitting a surface and does not stick to objects. However, it can produce a “sandlike” accumulation like snow.

Freezing rain forms when warm temperatures aloft, generally several degrees above freezing, produces rain that falls onto a surface with temperatures below 32 degrees. This causes the liquid rain to freeze on impact to objects such as trees, power lines, cars, and roads forming a coating or glaze of ice. Even a small amount of freezing rain on roads can create a significant travel hazard.


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