An ice storm is a type of winter storm characterized by freezing rain, also known as a glaze event The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least 0.25-inch (6.4 mm) of ice on exposed surfaces. From 1982 to 1994, ice storms were more common than blizzards in the U.S., averaging 16 per year.
Ice Storms are generally not violent storms but instead are commonly perceived as gentle rains occurring at temperatures just below freezing.
Effects of Ice Storms
The freezing rain from an ice storm covers everything with heavy, smooth glaze ice. In addition to hazardous driving or walking conditions, the weight of ice on branches or even whole trees may cause trees and branches to break from the weight of ice. Falling branches can block roads, tear down power and telephone lines, and cause other damage.
Falling trees and tree branches can break power lines and can also break and bring down power/utility poles; even electricity pylons with steel frames.
The weight of ice can also cause sagging power lines, which can also break power lines.
Severe ice storms with many damage incidents can cause power outages to last from several days to a month. According to most meteorologists, just one quarter of an inch of ice accumulation can add about 500 pounds (230 kg) of weight per line span. Damage from ice storms is easily capable of shutting down entire metropolitan areas.
Ice accretion is the process by which a layer of ice (icing) builds up on solid objects that are exposed to freezing precipitation or to supercooled fog or cloud droplets.
According to the American Meteorological Society, ice accretion on the earth’s surface usually refers to glaze formation, and the amount of ice can be roughly measured by an ice-accretion indicator. For airborne objects, ice accretion refers to any type of aircraft icing. See accretion.
Ice-accretion indicator
An instrument used to detect the occurrence of freezing precipitation. An Ice Accretion Indicator usually consists of a strip of sheet aluminum about 4 cm (1.5 in.) wide and is exposed horizontally, faceup, in the free air about 1 m above the ground.
In some parts of the United States, Ice Storms are known as silver frost or silver thaw — named after a deposit of glaze that builds up on trees, shrubs, and other exposed objects during a fall of freezing precipitation; the product of an ice storm.