WRAL WeatherCenter Blog

How is it possible that the snow we had this morning changed to rain so rapidly?

Posted February 3, 2007

MIKE MOSS SAYS:     Jeff,    On Thursday we had precipitation begin at a time when the atmosphere was just a little below freezing through a sizable depth from just above the surface to around 6-7,000 feet up, and then considerably colder above 10,000 feet or so. As the moisture that helped feed the precipitation flowed into the region from the southwest, it was followed closely by air that was warmer than the freezing point, especially in a layer from around 1-5,000 feet above the ground. For a short time, the effects of evaporative cooling and melting within this layer held the temperature close to the freezing mark and allowed snow to reach the ground. However, with continued warm air advection, together with a reduction in evaporative cooling once the lower atmosphere became nearly saturated, the temperatures in that layer steadily rose into the mid 30s and eventually to 40 degrees or more over much of the area, resulting in first a very brief transition to sleet  and freezing rain, and then rain as surface temperatures edged back up to 33 or 34 degrees.

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