I've thought about doing some research on black ice. It has seemed to me for years that black ice forms or doesn't form in response to what the weather has been over the previous 24-48 hours. I recall some mornings when the air temp was 34-35 and yet there was nasty black ice due to how cold the ground was from a recent cold snap. Conversely, if the weather has been warm, an air temp of 32 might not have led to black ice since the ground temp would have been warmer.
It's one of the those little weather phenomena's that I think about each winter when we have a black ice issue. This is the first winter that I can recall without a single instance of black ice.