What causing an ice?

Answer 1

Ice storms are basically a big freezing rain storm. As freezing rain begins to fall it forms coats of ice on the objects that it falls upon. The ice starts to accumulate and soon the weight of the ice upon tree branches, power lines, etc., becomes too much and they start to break.

But how come the precipitation isn't just snow, or just rain? Freezing rain only occurs in certain weather conditions. For freezing rain to occur there must be close to 100% humidity, with upward moving air to keep it that way. Also there must be three layers of air: one cold layer, near the surface of the Earth. One warm layer just above that. And one more cold layer, at the top, where the precipitation starts. It starts out as snow in the first cold layer, as it falls it hits the warm layer and melts into rain. It continues to fall and when it reaches the 2nd cold layer it starts to cool off again. It probably won't have time to freeze again before it hits the ground or an object, so when it hits an something that is 32°F or less, it freezes instantly. That is how freezing rain is formed.