Since today we have the possibility of experiencing some freezing rain later this evening and into the overnight hours, I felt that today would be a good day to cover how freezing rain occurs and what conditions are necessary in order to get freezing rain.
In the case of freezing rain, its all about the temperature at ground level and above the ground level. There must be a specific pattern of temps above ground level in order to get freezing rain. If not, you’ll receive just snow or just rain. The diagram below shows the temperature in relation to the height above the ground. Temperature is on the x axis, and height on the y axis. image from NOAA
In the above image, it shows the temperatures here in State College this morning. The black line represents the 0* C line and the red line is the actual temp. In this case all of the red line is to the left of the 0 C line, so in this case we would get just snow.
If we look farther to the west however in Dubois PA, we see something different. If you follow the red line down, just above the ground, it crosses the 0 C line, then back to its left. This means, as a snow flake falls from the upper atmosphere just above the ground it melts, but at the ground surface it freezes again, so hence the term freezing rain.