An ice storm is a dangerous weather event that occurs when snow melts in a warm layer in the atmosphere before freezing as it reaches the ground. Ice storms cause build-up of ice on roads, buildings, cars and trees. Driving conditions are often poor during and after an ice storm.
The phrase "ice storm" is a bit of a misnomer, as it is actually falling precipitation that freezes when it contacts ground-level. Public trucks often lay down salt or sand after an ice storm to melt the sheet of ice on the roads. Layers of ice also weigh on trees, contributing to branch decay.