Ice storm

Ice storms are weather phenomena caused by freezing rain. The falling rain comes into contact with surfaces and turns into a thin sheet of ice. Ice storms cause accidents, take power lines down and cause serious damage.

 Formation 

It starts with a layer of warmer (not freezing) air above a layer of huge-freezing temperatures lower down. Frozen precipitation melts to rain while falling into the warm air layer, and then begins to refreeze in the cold layer below. 
If the precipitate refreezes while still in the air, it will land on the ground as sleet. 
Or, the liquid droplets continue to fall without freezing. They pass through the cold air just above the surface. This thin layer of air cools the rain to a temperature below freezing (), but the drops themselves do not freeze. This is a phenomenon called supercooling. When the supercooled drops strike ground or anything else below  (e.g. power lines, tree branches, aircraft), a layer of ice builds up, hence "freezing rain".

 Reeferences 

Category:Severe weather
Category:Ice