Freezing Rain: Is It Rain, or Ice?

Freezing Rain Forms Glaze Ice and Ice Storms

freezing rain icicles
Accumulating freezing rain is a major cause of ice storms. Joanna Cepuchowicz/EyeEm/Getty Images

While beautiful to look at, freezing rain is one of the most hazardous types of winter precipitation. Accumulations of just several tenths of an inch of freezing rain may not sound significant, but are more than enough to break tree limbs, down power lines (and cause power outages), and coat and cause slick roadways.

The Midwest often gets devastating storms of this nature.

Rain that Freezes "On Contact"

Freezing rain is a bit of a contradiction.

The freezing part of its name implies frozen (solid) precipitation, but the rain implies it's a liquid. So, which is it? Well, it's kind of both.

Freezing rain happens when precipitation falls as liquid raindrops, then freezes as it hits individual objects on the ground whose temperatures are below 32 degrees Fahrenheit. The ice that results is called glaze ice because it covers the objects in a smooth coating. This happens in winter whenever temperatures at ground-level are below freezing but the layer of air overhead is warm at mid- and high levels of the atmosphere. So it is the temperature of objects at the earth's surface, not the rain itself, that determines if the precipitation will freeze.

It's important to note that freezing rain is in liquid form until it strikes a cold surface. Oftentimes, the water droplets are supercooled (their temperature is below freezing, yet they remain liquid) and freeze on contact.

How Fast Does Freezing Rain Freeze?

While we say that freezing rain freezes "on impact" when it strikes a surface, in reality, it takes a little time for the water to turn to ice. (How long depends on the temperature of the water drop, the temperature of the object the drop strikes, and the size of the drop.

The quickest drops to freeze will be small, supercooled drops that hit objects whose temperatures are well below 32 degrees.) Because freezing rain doesn't necessarily freeze right away, icicles and dripping icicles will sometimes develop.  

Freezing Rain vs. Sleet

Freezing rain and sleet are similar in a lot of ways. They both start out high in the atmosphere as snow, then melt as they fall into a "warm" (above freezing) layer of air. But while the partially melted snowflakes that eventually turn into sleet will fall through a brief warm layer, then re-enter a deep enough cold layer to turn back into ice (sleet), in a freezing rain setup, the melted snowflakes don't have enough time to freeze (into sleet) before reaching the ground since the layer of cold air is too thin.  

Sleet not only differs from freezing rain in how it forms, but what it looks like. Whereas sleet appears as tiny clear ice pellets that bounce when they hit the ground, freezing rain coats the surfaces it strikes with a layer of smooth ice. 

Why Doesn't It Just Snow?

In order to get snow, temperatures throughout the atmosphere would need to remain below-freezing with no warm layer to be found.

Remember, if you want to know the type of precipitation you'll get at the surface in wintertime, you'll want to look at what the temperatures are (and how they're changing) from high up in the atmosphere all the way down to the surface.

Here's the bottom line:

  • Snow forms if the entire layer of air -- aloft and near the ground -- is sub-freezing.
  • Sleet forms if the layer of sub-freezing air is fairly deep (approx. 3,000 to 4,000 feet thick).
  • Freezing rain forms if the sub-freezing layer is very shallow, with cold temperatures at the surface only.
  • Rain forms if the cold layer is too shallow.

The METAR code for freezing rain is FZRA.

Edited by Tiffany Means