Why not snow?

Our forecasts for this weekend were calling for some light additional snowfall. So, what happened? On the backside of the low pressure system that brought snow (some heavy) to our area on Friday, we’ve got some cold air in place. However, not all layers of the atmosphere have mixed – meaning that it may be cold at the surface of the earth, but there is a layer (or layers) a few thousand feet up that may be just above freezing. Without all of that cold air mixing through, that allows the snow (which falls from thousands of feet higher) to melt through that above-32° layer and then hit the surface as a raindrop. But, with surface temps below freezing, the raindrop freezes on contact. That’s why we had freezing drizzle yesterday and exactly why we had freezing rain and sleet this morning, leaving roads, sidewalks, and cars with a dangerous glazing of ice. The good news is that the bulk of the precipitation is now over, and most forecast models suggest those layers in the atmosphere will mix by this afternoon, allowing any remaining precipitation to stay frozen as light snow.

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