Ice storm facts for kids

Kids Encyclopedia Facts
Ice Storm 2013, Guelph 08
After 2013 Ice Storm in Guelph, Ontario, Canada

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.

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 and averaged 16 per year. They are generally not violent storms but instead are commonly perceived as gentle rains occurring at temperatures just below freezing.

Formation

Precipitation by type
A graph showing the formation of different kinds of precipitation.

It starts with a layer of warmer (not freezing) air above a layer of sub-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.

  1. If the precipitate refreezes while still in the air, it will land on the ground as sleet.
  2. 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 (0 °C or 32 °F), but the drops themselves do not freeze. This is a phenomenon called supercooling.
    When the supercooled drops strike ground or anything else below 0 °C (32 °F) (e.g. power lines, tree branches, aircraft), a layer of ice builds up, hence "freezing rain".

Effect

Ice storm
Power lines sagging after an ice storm. Besides disrupting transportation, ice storms can disrupt utilities by snapping lines and poles
Ice Storm by NOAA
Devastation caused by an ice storm

The freezing rain from an ice storm covers everything with heavy, smooth glaze ice. In addition to hazardous driving or walking conditions, branches or even whole trees may break from the weight of ice. Falling branches can block roads, tear down power and telephone lines, and cause other damage. Even without falling trees and tree branches, the weight of the ice itself can easily snap power lines and also break and bring down power/utility poles; even electricity pylons with steel frames. This can leave people without power for anywhere 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.

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Ice storm Facts for Kids. Kiddle Encyclopedia.