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An ice storm, also known as a glaze event or a silver storm is a type of winter storm characterized by freezing rain. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least of
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
on exposed surfaces. They are generally not violent storms but instead are commonly perceived as gentle rains occurring at temperatures just below freezing.


Formation

The formation of ice begins with a layer of above-freezing air above a layer of sub-freezing temperatures closer to the surface. Frozen precipitation melts to rain while falling into the warm air layer, and then begins to refreeze in the cold layer below. If the precipitate refreezes while still in the air, it will land on the ground as sleet. Alternatively, the liquid droplets can continue to fall without freezing, passing through the cold air just above the surface. This thin layer of air then cools the rain to a temperature below freezing (). However, the drops themselves do not freeze, a phenomenon called
supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...
(or forming " supercooled drops"). When the supercooled drops strike ground or anything else below (e.g. power lines, tree branches, aircraft), a layer of ice accumulates as the cold water drips off, forming a slowly thickening film of ice, hence freezing rain. While meteorologists can predict when and where an ice storm will occur, some storms still occur with little or no warning. In the United States, most ice storms occur in the northeastern region, but damaging storms have occurred farther south; an ice storm in February 1994 resulted in tremendous ice accumulation as far south as Mississippi, and caused reported damage in nine states.


Effect

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 of ice accumulation can add about of weight per line span. Damage from ice storms is easily capable of shutting down entire metropolitan areas. Additionally, the loss of power during ice storms has indirectly caused numerous illnesses and deaths due to unintentional carbon monoxide (CO) poisoning. At lower levels, CO poisoning causes symptoms such as nausea, dizziness, fatigue, and headache, but high levels can cause unconsciousness, heart failure, and death. The relatively high incidence of CO poisoning during ice storms occurs due to the use of alternative methods of heating and cooking during prolonged power outages, common after severe ice storms. Gas generators, charcoal and propane barbecues, and
kerosene heater A kerosene heater, also known as a paraffin heater, is typically a portable, unvented, kerosene-fueled, space (i.e., convectional) heating device. In Japan and other countries, they are a primary source of home heat. In the United States and ...
s contribute to CO poisoning when they operate in confined locations. CO is produced when appliances burn fuel without enough oxygen present, such as basements and other indoor locations. Loss of electricity during ice storms can indirectly lead to hypothermia and result in death. It can also lead to ruptured pipes due to water freezing inside the pipes.


Gallery

File:Trees with Ice.JPG, A tree covered in ice File:Frozen pinecone.JPG, Detail of a
pinecone A conifer cone (in formal botanical usage: strobilus, plural strobili) is a seed-bearing organ on gymnosperm plants. It is usually woody, ovoid to globular, including scales and bracts arranged around a central axis, especially in conifers an ...
covered in ice File:Tree branch after ice storm.JPG, A buildup of ice on a branch after an ice storm File:Car Ice Storm.jpg, Car after an ice storm File:Freezing Willow.JPG, A weeping willow tree damaged by an ice storm


See also

* Freezing rain *
Ice pruning Ice pruning is the natural process of selective vegetative pruning on the windward side of a plant, executed by the impact of ice and snow particles driven by wind.William M. Marsh (1978) ''Environmental Analysis: For Land Use and Site Planning'', ...
*
List of ice storms This is a list of notable ice storms. 1940s *Great Ice Storm of November 23–25, 1940. 1970s *Twin North Carolina Ice Storms of January 12–13 and 19-20, 1978 1990s *Western and Northern NY Ice Storm of March 3–4, 1991 *January 1998 Nort ...
* Power outage * Sperry–Piltz Ice Accumulation Index


References


External links


Ice Storms
at The Weather Channel
U.S. Billion-dollar Weather and Climate Events
{{DEFAULTSORT:Ice Storm Road hazards Snow or ice weather phenomena