In the image (left) the green dashed line is the temperature in respect to elevation. The surface temperature is 25°F (-4°C), and it increases with height before decreasing near the middle of the troposphere. However, since the temperature remains below freezing throughout, any precipitation that falls will remain as snow.

In this image the surface temperature is higher, 27°F (-3°C). Also as elevation increases, the temperature increases to a point where some of the atmosphere is above freezing before the temperature lowers again to below freezing.

As snow falls into the layer of air where the temperature is above freezing, the snow flakes partially melt. As the precipitation reenters the air that is below freezing, the precipitation will re-freeze into ice pellets that bounce off the ground, commonly called sleet. The most likely place for freezing rain and sleet is to the north of warm fronts. The cause of the wintertime mess is a layer of air aloft that is above freezing.

Freezing rain will occur if the warm layer in the atmosphere is deep with only a shallow layer of air at the surface that is below freezing. The precipitation can begin as either rain and/or snow, but it all melts into rain in the warm layer. The rain falls back into air that is below freezing, but since the depth is shallow, the rain does not have time to freeze into sleet.

The rain freezes on contact when it hits the ground or objects such as bridges and vehicles that are at temperatures below 32 degrees Fahrenheit. Some of the most disastrous winter weather storms are due primarily to freezing rain.