Management plans for urban trees should incorporate information on the ice storm susceptibility of trees to limit potential ice damage, to reduce hazards resulting from ice damage, and to restore urban tree populations following ice storms. Susceptibility ratings of species commonly planted in urban areas are presented for use in developing and maintaining healthy urban tree populations. They vary considerably in their severity and frequency. Ice storms are result of the ice formation process, which is influenced by general weather patterns. This generally occurs when a winter warm front passes through an area after the ground-level temperature reaches or falls below freezing.
Rain falls through layers of cooler air without freezing, becoming supercooled.
Periodically, other climatic events, including stationary, occluded, and cold fronts, also result in ice storms. Conditions that result in ice storms are most prevalent in the midwestern and eastern parts of the United States. Accumulations of ice can increase the branch weight of trees by 30 times or more. Ice formation generally ranges from a trace to 1 inch in additional stem diameter. Branch failure occurs when loading from the weight of ice exceeds wood resistance or when constant loading further stresses a weakened area in a branch.