Little known facts about ice storms
Unlike snow, which is frozen water vapor, ice is all water, making it much more difficult to melt. And 1.67 inches of liquid precipitation (sleet) would have made about 15 inches of snow had it fallen in that form. AND, the higher the water content, the more heat energy is required to melt it.
Which is to say that you can have an ice storm on, oh...say, Wednesday and still have ice on the roads by, say...the following TUESDAY.