Ice storm

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Devastation caused by an ice storm Ice Storm by NOAA.jpg
Devastation caused by an ice storm

An ice storm, also known as a glaze event or a silver storm is a type of winter storm characterized by freezing rain. [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 (6.4 mm) of ice on exposed surfaces. [2] [3] They are generally not violent storms but instead are commonly perceived as gentle rains occurring at temperatures just below freezing.



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

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 (0 °C or 32 °F). However, the drops themselves do not freeze, a phenomenon called supercooling (or forming "supercooled drops"). 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 accumulates as the cold water drips off, forming a slowly thickening 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] 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. [7] [8]


Power lines and poles pulled down after an ice storm. Besides disrupting transportation, ice storms can disrupt utilities by snapping lines and poles. A street in Elora, Ontario, after an ice storm, early 1900s.jpg
Power lines and poles pulled down after an ice storm. Besides disrupting transportation, ice storms can disrupt utilities by snapping lines and poles.

The freezing rain from an ice storm covers everything with heavy, smooth glaze ice. [9] 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 0.25-inch (6.4 mm) 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.

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. [10] 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. [11] Gas generators, charcoal and propane barbecues, and kerosene heaters contribute to CO poisoning when they operate in confined locations. [10] CO is produced when appliances burn fuel without enough oxygen present, [12] 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.

See also

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<span class="mw-page-title-main">Frost</span> Coating or deposit of ice

Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor to ice as the water vapor reaches the freezing point. In temperate climates, it most commonly appears on surfaces near the ground as fragile white crystals; in cold climates, it occurs in a greater variety of forms. The propagation of crystal formation occurs by the process of nucleation.

<span class="mw-page-title-main">Hail</span> Form of solid precipitation

Hail is a form of solid precipitation. It is distinct from ice pellets, though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fall in cold weather, while hail growth is greatly inhibited during low surface temperatures.

<span class="mw-page-title-main">Ice</span> Frozen water: the solid state of water

Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 °F Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

<span class="mw-page-title-main">Freezing rain</span> Rain maintained at temperatures below freezing

Freezing rain is rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow or ice pellets, freezing rain is made entirely of liquid droplets. The raindrops become supercooled while passing through a sub-freezing layer of air hundreds of meters above the ground, and then freeze upon impact with any surface they encounter, including the ground, trees, electrical wires, aircraft, and automobiles. The resulting ice, called glaze ice, can accumulate to a thickness of several centimeters and cover all exposed surfaces. The METAR code for freezing rain is FZRA.

<span class="mw-page-title-main">Winter storm</span> Event in which the varieties of precipitation are formed that only occur at low temperatures

A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, mixed snow and rain, or freezing rain. In temperate continental climates, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. A snowstorm with strong winds and other conditions meeting certain criteria is called a blizzard.

<span class="mw-page-title-main">Black ice</span> Thin coating of glazed ice on a surface

Black ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. The typically low levels of noticeable ice pellets, snow, or sleet surrounding black ice means that areas of the ice are often practically invisible to drivers or people stepping on it. There is, thus, a risk of slippage and subsequent accident due to the unexpected loss of traction.

<span class="mw-page-title-main">Frazil ice</span> Collections of ice crystals in open water

Frazil ice is a collection of loose, randomly oriented ice crystals millimeter and sub-millimeter in size, with various shapes, e.g. elliptical disks, dendrites, needles and of an irregular nature. Frazil ice forms during the winter in open-water reaches of rivers as well as in lakes and reservoirs, where and when the water is in a turbulent state, which is, in turn, induced by the action of waves and currents. Turbulence causes the water column to become supercooled, as the heat exchange between the air and the water is such that the water temperature drops below its freezing point. The vertical mixing associated with that turbulence provides enough energy to overcome the crystals' buoyancy, thus keeping them from floating at the surface. Frazil ice also forms in oceans, where windy conditions, wave regimes and cold air also favor the establishment of a supercooled layer. Frazil ice can be found on the downwind side of leads, and in polynyas. In these environments, that ice can eventually accumulate at the water surface into what is referred to as grease ice.

<span class="mw-page-title-main">January 1998 North American ice storm</span> January 1998 ice storm in North America

The North American Ice Storm of 1998 was a massive combination of five smaller successive ice storms in January 1998 that struck a relatively narrow swath of land from eastern Ontario to southern Quebec, New Brunswick and Nova Scotia in Canada, and bordering areas from northern New York to central Maine in the United States. It caused massive damage to trees and electrical infrastructure throughout the area, leading to widespread long-term power outages. Millions were left in the dark for periods varying from days to several weeks, and in some instances, months. It led to 34 fatalities, a shutdown of activities in large cities like Montreal and Ottawa, and an unprecedented effort in reconstruction of the power grid. The ice storm led to the largest deployment of Canadian military personnel since the Korean War, with over 16,000 Canadian Forces personnel deployed, 12,000 in Quebec and 4,000 in Ontario at the height of the crisis.

<span class="mw-page-title-main">Rime ice</span>

Rime ice forms when supercooled water liquid droplets freeze onto surfaces. Meteorologists distinguish between three basic types of ice forming on vertical and horizontal surfaces by deposition of supercooled water droplets. There are also intermediate formations.

A winter storm warning is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the National Weather Service (NWS) in the United States to alert the public that a winter storm is occurring or is about to occur in the area, usually within 36 hours of the storm's onset.

The Wegener–Bergeron–Findeisen process, is a process of ice crystal growth that occurs in mixed phase clouds in regions where the ambient vapor pressure falls between the saturation vapor pressure over water and the lower saturation vapor pressure over ice. This is a subsaturated environment for liquid water but a supersaturated environment for ice resulting in rapid evaporation of liquid water and rapid ice crystal growth through vapor deposition. If the number density of ice is small compared to liquid water, the ice crystals can grow large enough to fall out of the cloud, melting into rain drops if lower level temperatures are warm enough.

<span class="mw-page-title-main">Ice pellets</span> Precipitation consisting of small, translucent balls of ice

Ice pellets are a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel which is made of frosty white opaque rime, and from a mixture of rain and snow which is a slushy liquid or semisolid. Ice pellets often bounce when they hit the ground or other solid objects, and make a higher-pitched "tap" when striking objects like jackets, windshields, and dried leaves, compared to the dull splat of liquid raindrops. Pellets generally do not freeze into other solid masses unless mixed with freezing rain. The METAR code for ice pellets is PL.

<span class="mw-page-title-main">Freezing drizzle</span> Light liquid precipitation that freezes on or near a cold surface

Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ.

<span class="mw-page-title-main">Snow in Florida</span> Snow events in Florida, USA

It is very rare for snow to fall in the U.S. state of Florida, especially in the central and southern portions of the state. With the exception of the far northern areas of the state, most of the major cities in Florida have never recorded measurable snowfall, though trace amounts have been recorded, or flurries in the air observed few times each century. According to the National Weather Service, in the Florida Keys and Key West there is no known occurrence of snow flurries since the European colonization of the region more than 300 years ago. In Miami, Fort Lauderdale, and Palm Beach there has been only one known report of snow flurries observed in the air in more than 200 years; this occurred in January 1977. In any event, Miami, Fort Lauderdale, and Palm Beach have not seen snow flurries before or since this 1977 event.

<span class="mw-page-title-main">February 2007 North American blizzard</span>

The February 2007 North American blizzard was a massive winter storm that affected most of the eastern half of North America, starting on February 12, 2007 and peaking on Valentine's Day, February 14. The storm produced heavy snowfalls across the midwestern United States from Nebraska to Ohio and produced similar conditions across parts of the northeastern United States, and into Canada in Ontario, Quebec and New Brunswick. Significant sleet and freezing rain fell across the southern Ohio Valley and affected portions of the east coast of the United States, including the cities of Boston, Baltimore, Washington, D.C., New York City and Philadelphia.

<span class="mw-page-title-main">Glaze (ice)</span> Coating of ice on objects

Glaze or glaze ice, also called glazed frost, is a smooth, transparent and homogeneous ice coating occurring when freezing rain or drizzle hits a surface. It is similar in appearance to clear ice, which forms from supercooled water droplets. It is a relatively common occurrence in temperate climates in the winter when precipitation forms in warm air aloft and falls into below-freezing temperature at the surface.

<span class="mw-page-title-main">Rain and snow mixed</span> Form of precipitation consisting of rain and melting snow

Rain and snow mixed is precipitation composed of a mixture of rain and partially melted snow. Unlike ice pellets, which are hard, and freezing rain, which is fluid until striking an object where it fully freezes, this precipitation is soft and translucent, but it contains some traces of ice crystals from partially fused snowflakes, also called slush. In any one location, it usually occurs briefly as a transition phase from rain to snow or vice versa, but hits the surface before fully transforming. Its METAR code is RASN or SNRA.

<span class="mw-page-title-main">December 1969 nor'easter</span> Strong winter storm that affected the northeastern US

The December 1969 nor'easter was a strong winter storm that mainly affected the Northeastern United States and southern Quebec between December 25 and December 28, 1969. The multi-faceted storm system included a tornado outbreak, record snow accumulations, a damaging ice storm, and flooding rains.

<span class="mw-page-title-main">2011 Groundhog Day blizzard</span> 2011 blizzard affecting the U.S. and Canada

The 2011 Groundhog Day blizzard was a powerful and historic winter storm that affected large swaths of the United States and Canada from January 31 to February 2, 2011, especially on Groundhog Day. During the initial stages of the storm, some meteorologists predicted that the system would affect over 100 million people in the United States. The storm brought cold air, heavy snowfall, blowing snow, and mixed precipitation on a path from New Mexico and northern Texas to New England and Eastern Canada. The Chicago area saw 21.2 inches (54 cm) of snow and blizzard conditions, with winds of over 60 mph (100 km/h). With such continuous winds, the blizzard continued to the north and affected Eastern and Atlantic Canada. Blizzard conditions affected many other large cities along the storm's path, including Tulsa, Oklahoma City, Kansas City, St. Louis, Springfield, El Paso, Las Cruces, Des Moines, Milwaukee, Detroit, Chicago, Indianapolis, Dayton, Cleveland, New York City, New York's Capital District, and Boston. Many other areas not normally used to extreme winter conditions, including Albuquerque, Dallas and Houston, experienced significant snowfall or ice accumulation. The central Illinois National Weather Service in Lincoln, Illinois, issued only their fourth blizzard warning in the forecast office's 16-year history. Snowfall amounts of 20 to 28 inches were forecast for much of Northern and Western Illinois.

<span class="mw-page-title-main">February 15–20, 2021 North American winter storm</span> Category 3 winter storm and ice storm in the United States

The February 15–20, 2021 North American winter storm, also unofficially referred to as Winter Storm Viola, was a significant and widespread snow and ice storm across much of the United States, Northern Mexico, and Southern Canada. The system started out as a winter storm on the West Coast of the United States on February 15, later moving southeast into the Southern Plains and Deep South from February 16–17. It then moved into the Appalachian Mountains and Northeastern United States, before finally moving out to sea on February 20. The storm subsequently became a powerful low pressure system over the North Atlantic, before eventually dissipating on February 26.


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