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How could sleet happen at 16 degrees?

Dear Tom,

My sister in Boston told me it was 16 degrees and sleeting. How could sleet happen at such a low temp?

Waterford, Wisconsin

Dear Shari,

Sleet and freezing rain can fall with very low surface temperatures. It’s the temperature profile in the layer from the clouds to the surface that determines what type of precipitation reaches the ground. Though sleet and freezing rain are quite different, the atmospheric conditions that produce them are identical: rain, originating in warmer air aloft, falling into subfreezing air at ground level. If the depth of subfreezing air is great enough and if its temperature is low enough, the raindrops will freeze before reaching the surface, and the result is sleet or ice pellets. If the raindrops don’t freeze on the way down but freeze on impact to glaze the ground and exposed objects, the result is freezing rain.

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