What causes freezing rain to occur?

Question

Yes, I know that freezing rain is rain that freezes when it comes in contact with a sub-freezing surface.

But my question, why does this happen? In other words, why is temperature warm enough at cloud level and cold enough at ground level?

Could it be because of weather fronts?

Answer 1

Freezing rain is a type of precipitation that begins as snow at higher altitude, falling from a cloud towards earth, melts completely on its way down while passing through a layer of air above freezing temperature, and then encounters a layer below freezing at a lower level to become supercooled. This water will then freeze upon impact with any object it encounters.

Answer 2

In wintry conditions, when temperatures at cloud level are below zero, any water droplets that fall from clouds will be supercooled. This means that they are likely to freeze as soon as they encounter a colder layer of air or a surface whose temperature is below 32° F (0° C). Precipitation that freezes in either of these ways is known as freezing rain.  

Answer 3

The usual setup that leads to freezing rain is simply a layer of above freezing air above a sub freezing layer.  This is not unusual during very cold arctic air outbreaks, where the very cold and heavy arctic air slips under a warmer airmass.  Precipitation is produced and falls through the warmer air aloft and melts (if it was frozen to begin), then as it falls through the sub-freezing layer at and just above the surface, the rain is chilled and freezes on impact with the sub-freezing surfaces.  The cold surface airmass must not be too deep, otherwise the chilled raindrops can freeze before reaching the surface, resulting in sleet.