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An ice storm is a type of winter storm characterized by freezing rain, also known as a glaze event or in some parts of the United States as a silver thaw[1]. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least 0.25-inch (0.64 cm) of ice on exposed surfaces.[2] From 1982 to 1994, ice storms were more common than blizzards and averaged 16 per year.[3]



A graph showing the formation of different kinds of precipitate as a function of height and temperature.

Ice storms occur when a layer of warm air is between two layers of cold air. Frozen precipitation melts while falling into the warm air layer, and then proceeds to refreeze in the cold layer above the ground. If the precipitate is partially melted, it will land on the ground as sleet. However, if the warm layer completely melts the precipitate, becoming rain, the liquid droplets will continue to fall, and pass through a thin layer of cold air just above the surface. This thin layer of air then cools the rain to a temperature below freezing (0 °C). However, the drops themselves do not freeze, a phenomenon called supercooling (or forming "supercooled drops"). When the supercooled drops strike ground below 0 °C or anything else below 0 °C (power lines, tree branches, aircraft), they instantly freeze, forming a thin film of ice, hence freezing rain.[4][5][6]

While meteorologists can predict when and where an ice storm will occur, some storms still occur with little or no warning.[5] Most ice storms are thought to form primarily in the north-eastern US, 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. More timber was damaged than that caused by Hurricane Camille. An ice storm in eastern Washington in November 1996 directly followed heavy snowfall. The combined weight of the snow and 25 millimetres (0.98 in) to 37 millimetres (1.5 in) of ice caused considerable widespread damage. This was considered to be the most severe ice storm in the Spokane area since 1940.[3]


Wires sagging after an ice storm. Besides disrupting transportation, ice storms can disrupt utilities by snapping power lines and power poles.

The freezing rain from an ice storm covers everything with heavy, smooth glaze ice. Ice-covered roads become slippery and hazardous, as the ice causes vehicles to skid out of control, which can cause devastating car crashes as well as pile-ups. Pedestrians are severely affected as sidewalks become slippery, causing people to slip and fall, and outside stairs can become an extreme injury hazard.

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 steel frame electricity pylons have been sent crashing to the ground by the weight of the ice. 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 of weight per line span. Damage from ice storms is highly 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[7]. 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 during severe ice storms[8]. Gas generators, charcoal and propane barbecues, and kerosene heaters contribute to CO poisoning when they operate in confined locations[7]. CO is produced when appliances burn fuel without enough oxygen present [9], such as basements and other indoor locations. Loss of electricity during ice storms can also easily lead to hypothermia and even death from hypothermia. It can also lead to ruptured pipes due to water freezing inside the pipes.

Tree sensitivity to sap coloration and resistance to crown damage from an ice storm.[3]
Sensitivity to sap coloration Resistance to ice damage to crown
Low or average Average or strong Strong



Notable ice storms

An ice storm which struck northern Idaho in January 1961 set a record for thickest recorded ice accumulation from a single storm in the United States, at 8 inches.[10][11]

The North American ice storm of 1998 occurred during January 5–9, 1998. It was one of the most damaging and costly ice storms in North American history. The storm caused massive power failures in several large cities on the East Coast of the United States. The most affected area was extreme eastern Ontario and southwestern Quebec in Canada, where over 3 million people were without power for up to a month and a half. Whole trees snapped and electrical pylons were completely flattened under the weight of the accumulated ice.[citation needed]

The Northeastern United States was impacted by a major ice storm on December 11–12, 2008, which left about 1.25 million homes and businesses without power. Areas impacted with 3/4" to 1" of ice accumulation included eastern New York in the Albany area, central and western Massachusetts, southern New Hampshire, coastal and south-central Maine, Pennsylvania in the Pocono Mountains region, northwestern Connecticut, and southern Vermont.[citation needed]

In late January, 2009, ice storms covered several U.S. states, including Arkansas and Kentucky. Most areas affected saw over 2" of ice accumulation, and between 1"–5" of snow on top of the ice. This ice storm left well over 2 million people without power at its peak and killed 55 people, 24 in Kentucky.[12] Rural Water Associations in Arkansas and Kentucky activated emergency response plans to deal with power loss to small water utilities across their states. Neighboring state Rural Water Associations, including experienced emergency responders from Louisiana and Florida, loaned equipment and manpower to assist the hardest-hit areas.[13][14]



  1. ^ "Glossary of Meteorology, Section S". AMS Glossary. Retrieved 2009-01-09. 
  2. ^ Hauer, Richard J.; Dawson, Jeffrey O.; Werner, Les P. (2006). Trees and Ice Storms - The Development of Ice Storm-Resistant Urban Tree Populations (2 ed.). College of Natural Resources, University of Wisconsin–Stevens Point, and the Department of Natural Resources and Environmental Sciences and the Office of Continuing Education, University of Illinois at Urbana-Champaign. 
  3. ^ a b c Irland, Lloyd C. (2000-11-15). "Ice Storms and forest impacts". The Science of the Total Environment 262 (1): 231–242. doi:10.1016/S0048-9697(00)00525-8. ISSN 00489697. 
  4. ^ Gay, David A.; Robert E. Davis (1993-12-30). "Freezing rain and sleet climatology of the southeastern USA". Climate Research 3 (1): 209–220. doi:10.3354/cr003209. 
  5. ^ a b "Ice Storms". City of Savannah, Georgia. Retrieved 2009-01-08. 
  6. ^ University of Illinois. "Cyclones and Fronts: the definition of freezing rain". Retrieved 2009-01-09. 
  7. ^ a b Hartling, L.; Brison, R.J.; Pickett, W. (1998-11). "Cluster of Unintentional Carbon Monoxide Poisonings Presenting to the Emergency Departments of Kingston, Ontario during 'Ice Storm 98'". Canadian Journal of Public Health 89 (3): 388–390. 
  8. ^ Wrenn, K.; Conners, G.P. (1997). Carbon monoxide poisoning during ice storms: A tale of two cities (4 ed.). Journal of Emergency Medicine. 
  9. ^ Griefe, A.L.; Goldenhar, L.M.; Freund, E. (1997). Carbon monoxide poisoning from gasoline-powered engines: Risk perception among midwest flood victims (3 ed.). American Journal of Public Health. 
  10. ^ National Weather Service — January 3, 2010. Accessed 1-3-2010.
  11. ^ - On this day in weather history ...
  12. ^ "National Death Toll Hits 55 in Ice Storm, 24 in KY". ABC News. 2009. Retrieved 2009-02-02. 
  13. ^ Jan. 29 2009 "Arkansas Rural Water fighting ice to bring generators to powerless utilities". National Rural Water Association. 2009. Jan. 29 2009. Retrieved 2009-01-29. 
  14. ^ "700,000 without power - Kentucky Rural Water Association helps with recovery from ice storm". National Rural Water Association. 2009. Retrieved 2009-02-02. 

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