Freezing rain is a meterological phenomenon that causes rain to freeze upon impact.

Freezing rain happens when frozen water (in the form of hail or snowflakes) enters a warm pocket of air at around 10,000ft and changes state into a supercooled liquid. As the rain approaches the surface it enters a pocket of cold air, where the temperature drops to just below freezing. When the water hits the earth's surface, it freezes instantly.

In graph form1, the process looks like this:

            _______________________________
           |          Temperature          |
           | Below         |         Above |
           | Freezing      |      Freezing |
            _______________________________
           |               |               |
           |          \    |               |
           |           \   |               |
           |            \  |               |
           |             \ |               |
           |              \|               |
           |               |    - 10,000ft |
           |               |\              |
           |               | \             |
           |               | /             |
           |               |/              |
           |               |     - 2,000ft |
           |              /|               |
           |             / |     - Surface |
            _______________________________

In order for freezing rain to occur, the surface temperature must be below freezing point. This encourages the rapidly cooling liquid to freeze at the moment that it strikes the ground. The impact helps perturb a phase transition; ice crystals form rapidly on the surface. The chilled, shallow air keeps the ice frozen.

Freezing rain plunders everything in its path. The rain moulds itself to every surface as it freezes, which creates a blanket of ice across roads and footpaths. The "glaze" of ice is more condensed and tightly-packed than usual, which makes it harder to break and melt. Telegraph wires, power lines and tree branches often snap under its weight.

If freezing rain is predicted for your area, move all of your possessions inside, clear away any dead or dying branches from nearby trees, stock up on candles and good books, and stay inside during the storm. Apparently the formation of freezing rain is beautiful to watch; they say that it is pretty, in a deadly sort of way.

The most notorious case of freezing rain occured in Canada in 1998 and is often known as the Great Ice Storm.


1. This chart was kindly provided in graphic form by the Shreveport Weather Service and can be viewed at http://www.srh.noaa.gov/shv/FzRain.htm

When flying an aircraft through an inversion (where most supercooled water can be found) or any other low-temperature conditions, one must be very wary of freezing rain and aircraft icing. The ice coats the wings of the aircraft, adding so much weight and ruining the aerodynamics of the aircraft to such an extent that flying can become impossible. In extreme circumstances the controls can freeze over, but this doesn't usually occur (as the aircraft is most often already in serious trouble before that could happen).

There are two types of ice that result from freezing rain and aircraft icing; Rime Ice and Clear Ice (sometimes referred to as Sheet Ice). Rime ice is easier to remove if the aircraft is equipped with the necessary tools, and it also is more aerodynamically effecient. Clear ice is more difficult to remove and can bring an aircraft down in a matter of minutes.

Freezing rain most often occurs in an inversion (where the air is warmer higher up, but is colder closer to the ground). As the fancy graph in the writeup above shows, a water droplet formed in the "above freezing" section will travel into the cold air mass and become supercooled. An inversion can occur for many reasons, but the most common is when a warm front collides with a cold front. Because warm air rises, a warm front will "ride up" over the cold front (or an approaching cold front will "wedge under" a warm front). As the warm air rises, it begins to cool and cannot contain as much moisture, and it then rains.

 (CLOUD)
\ .  . .           WARM AIRMASS
 \. ..
  \.
   \              (= Warm air travelling this way
   ~\
     \
  ~ ~ \  
     ~ \ 
COLD    \
AIRMASS  \
          \
           \
---------------------------- (ground)
In my fancy-wancy diagram, you can see the rain (.) starting in the warm airmass, passing through the temperature layer (\) and entering the cold airmass. As it does so, it becomes supercooled water (~).

Freezing rain, simply put, is rain that freezes shortly after making contact with a surface, whether it be the pavement, your roof, or your glasses. The temperature of the rain clouds from which the devilish droplets fall is not low enough to cause the water to crystallize, creating snow, but the temperature closer to the ground is cold enough to freeze it there. This ensures that everything, and I mean everything, is covered in a medium to thick layer of ice, making travel increasingly difficult as the ice stacks upon itself. Want to go get a coffee at lunch? Not without falling on your ass and breaking your tailbone. Is your bus supposed to come after a designated wait time? Substitute that value into f(x)=3x^2 to get your actual wait time. Nothing moves. Except for your legs, uncontrollably and a little too fast, as you slip around helplessly like a greased bowling ball. The world is trapped in a hard, hard shell of motherfucking ice, man. Motherfucking ice.

I look to the sky, see the shrapnel of a frozen hell raining down upon me with nothing but my thin glasses to protect my fragile eyeballs. And i wonder why the fuck i live in a place where the abomination that is freezing rain is allowed to exist.

Freezing rain, man. God can be so cruel sometimes.

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