Freezing rain is
rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
maintained at temperatures below
freezing
Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...
by the ambient
air mass
In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to la ...
that causes
freezing
Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...
on contact with surfaces. Unlike
a mixture of rain and snow or
ice pellets
Ice pellets are a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel ("soft hail") which is made of frosty white opaque rime, and from a mixture of rain and snow which is a slushy ...
, freezing rain is made entirely of
liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
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
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 ...
, can accumulate to a thickness of several centimeters and cover all exposed surfaces. The
METAR
METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.
Raw METAR is the most common form ...
code for freezing rain is FZRA.
A storm that produces a significant thickness of glaze ice from freezing rain is often referred to as 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. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least of ice on e ...
. Although these storms are not particularly violent, freezing rain is notorious for causing travel problems on roadways, breaking tree limbs, and downing
power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...
s from the weight of accumulating ice. Downed
power lines
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is d ...
cause power outages in affected areas while accumulated ice can also pose significant overhead hazards. It is also known for being extremely dangerous to aircraft since the ice can effectively 'remould' the shape of the
airfoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
and
flight control surfaces
Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.
Development of an effective set of flight control surfaces was a critical advance in the development of aircraft. Ea ...
. (See
atmospheric icing
Atmospheric icing occurs in the atmosphere when water droplets suspended in air freeze on objects they come in contact with. It is not the same as freezing rain, which is caused directly by precipitation. Icing conditions can be particularly dang ...
.)
Mechanism
Freezing rain is often associated with the approach of a
warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fro ...
, when subfreezing air (temperatures at or below freezing) is trapped in the lowest levels of the atmosphere while warm air
advects is aloft.
This happens, for instance, when a low pressure system moves from the
Mississippi River
The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
Valley toward the
Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
and the
Saint Lawrence River
The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connectin ...
Valley of
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
during the cold season, with a strong high pressure system sitting further east. This setup is known as
cold-air damming
Cold air damming, or CAD, is a meteorology, meteorological phenomenon that involves a high-pressure area, high-pressure system (anticyclone) accelerating equatorward east of a north-south oriented mountain range due to the formation of a barrier je ...
, and is characterized by very cold and dry air at the surface within the region of high pressure. The warm air from the
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
is often the fuel for freezing precipitation.
Freezing rain develops when falling snow encounters a layer of warm air aloft, typically around the level, causing the snow to melt and become rain. As the rain continues to fall, it passes through a layer of subfreezing air just above the surface and cools to a temperature below freezing (). If this layer of subfreezing air is sufficiently deep, the raindrops may have time to freeze into
ice pellets
Ice pellets are a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel ("soft hail") which is made of frosty white opaque rime, and from a mixture of rain and snow which is a slushy ...
(sleet) before reaching the ground. However, if the subfreezing layer of air at the surface is very shallow, the rain drops falling through it will not have time to freeze and they will hit the ground as
supercooled rain. When these supercooled drops make contact with the ground, power lines, tree branches, aircraft, or anything else below , a portion of the drops instantly freezes, forming a thin film of ice, hence freezing rain. The specific physical process by which this occurs is called
nucleation
In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...
.
Observations
Surface observations by manned or automatic stations are the only direct confirmation of freezing rain. One can never ''see'' directly freezing rain, rain, or snow on any type of
weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly puls ...
, whether
Doppler or conventional. It is possible, however, to estimate the area covered by freezing rain with
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
indirectly.
The intensity of the radar echoes (
reflectivity
The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...
) is proportional to the form (water or ice) of the
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
and its diameter. In fact, rain has much stronger reflective power than snow, but its diameter is much smaller. So, the reflectivity of rain coming from melted snow is only slightly higher. In the layer where the snow is melting, however, the wet flakes still have a large
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
and are coated with water, so the radar returns are much stronger.
[
The presence of this brightband indicates the presence of a warm layer above ground where snow can melt. This could be producing rain on the ground or the possibility of freezing rain if the temperature is below freezing. The accompanying image shows how such an artifact can be located with a cross-section through radar data.][ The height and slope of the brightband will give clues to the extent of the region where melting is occurring. Then, it is possible to associate this clue with surface observations and numerical prediction models to produce output such as the ones seen on television weather programs, where radar echoes are shown distinctly as rain, mixed, and snow precipitations.
]
Effects
At ground level
Freezing rain often causes major power outages by forming glaze ice. When the freezing rain or drizzle is light and not prolonged, the ice formed is thin and usually causes only minor damage (relieving trees of their dead branches, etc.). When large quantities accumulate, however, it is one of the most dangerous types of winter hazard. When the ice layer exceeds approximately , tree limbs with branches heavily coated in ice can break off under the enormous weight and fall onto power lines. Windy conditions and lightning
Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
, when present, will exacerbate the damage. Power lines coated with ice become extremely heavy, causing support poles, insulators and lines to break. The ice that forms on roadways makes vehicle travel dangerous. Unlike snow, wet ice provides almost no traction, and vehicles will slide even on gentle slopes. Because freezing rain does not hit the ground as an ice pellet (called "sleet") but still as a rain droplet, it conforms to the shape of the ground, or object such as a tree branch or car. This makes one thick layer 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 ...
, often called "glaze".
Freezing rain and glaze ice on a large scale is called 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. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least of ice on e ...
. Effects on plants can be severe, as they cannot support the weight of the ice. Trees may snap as they are dormant and fragile during winter weather. Pine trees are also victims of ice storms as their needles will catch the ice, but not be able to support the weight. In February 1994, a severe ice storm caused over $1 billion in damage in the Southern United States, primarily in Mississippi, Tennessee, Alabama, and Western North Carolina, especially the Appalachians. One particularly severe ice storm struck eastern Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
and northern parts of New York and New England
New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...
in the North American ice storm of 1998.
File:Damaged trees in Ljubljana Trg MDB.jpeg, Tree downed by a thick layer of glaze in downtown Ljubljana
Ljubljana (also known by other historical names) is the capital and largest city of Slovenia. It is the country's cultural, educational, economic, political and administrative center.
During antiquity, a Roman city called Emona stood in the ar ...
, Slovenia
Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...
File:Freezing Rain on Tree Branch.jpg, Glaze on a tree in La Malbaie, Quebec
File:Zlodowacenie - Marznący deszcz 6.JPG, Ice on coniferous tree in Tomaszów Mazowiecki
Tomaszów Mazowiecki (, yi, טאָמעשעוו or ''Tomashuv'') is a city in central Poland with 60,529 inhabitants (2021). The fourth most populous city in the Łódź Voivodeship and the second with free public transport. In Tomaszów Mazowi ...
, Poland
Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...
File:Bent tree glaze ice Celje.jpg, A birch tree is badly bent under a thick layer of glaze ice in Celje
)
, pushpin_map = Slovenia
, pushpin_label_position = left
, pushpin_map_caption = Location of the city of Celje in Slovenia
, coordinates =
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, Slovenia
Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...
File:Ice storm in moscow.JPG, Aftermath of freezing rain in Moscow Oblast
Moscow Oblast ( rus, Моско́вская о́бласть, r=Moskovskaya oblast', p=mɐˈskofskəjə ˈobləsʲtʲ), or Podmoskovye ( rus, Подмоско́вье, p=pədmɐˈskovʲjə, literally "under Moscow"), is a federal subject of Rus ...
, Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, December 2010
File:Iced power lines.JPG, Power outages due to the weight of ice on lines or overhanging tree limbs
Aircraft
Freezing rain is considered to be an extreme hazard to aircraft, as it causes very rapid structural icing, freezing necessary components. Most helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
s and small airplanes lack the necessary deicing
Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
equipment to fly in freezing rain of any intensity, and heavy freezing rain can overwhelm even the most sophisticated deicing systems on large airplanes. Icing can increase an aircraft's weight but not typically enough to cause a hazard. The main danger comes from the ice changing the shape of its airfoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
s.
This will reduce lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobil ...
and increase drag. All three factors increase stalling speed and reduce aircraft performance, making it very difficult to climb or even maintain altitude.
An aircraft can most easily avoid freezing rain by moving into warmer air. Under most conditions, this would require aircraft to descend, which it can usually do safely and easily even with a moderate accumulation of structural ice. However, freezing rain is accompanied by a temperature inversion
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion of the air temperature lapse rate, in which case it is called a temperature inversion. No ...
aloft, meaning that aircraft are required to climb to move into warmer air, which is a potentially difficult and dangerous task with even a small amount of ice accumulation.
For example, in 1994, American Eagle Flight 4184
American Eagle Flight 4184, officially operating as Simmons Airlines Flight 4184, was a scheduled domestic passenger flight from Indianapolis, Indiana to Chicago, Illinois, United States. On , 1994, the performing this route flew into severe ...
encountered heavy air traffic and poor weather that postponed the arrival of this flight at Chicago
(''City in a Garden''); I Will
, image_map =
, map_caption = Interactive Map of Chicago
, coordinates =
, coordinates_footnotes =
, subdivision_type = Country
, subdivision_name ...
's O'Hare International Airport
Chicago O'Hare International Airport , sometimes referred to as, Chicago O'Hare, or simply O'Hare, is the main international airport serving Chicago, Illinois, located on the city's Northwest Side, approximately northwest of the Chicago Loop, ...
, where it was to have landed en route from Indianapolis, Indiana
Indianapolis (), colloquially known as Indy, is the state capital and most populous city of the U.S. state of Indiana and the seat of Marion County. According to the U.S. Census Bureau, the consolidated population of Indianapolis and Mari ...
. The ATR-72, a twin-engine turboprop carrying 68 people, entered a holding pattern southeast of O'Hare. As the plane circled, supercooled cloud droplets, freezing rain or freezing drizzle
Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ.
Formation
Although freezing drizzle and freezing rain are similar in that they both involve liquid precipitation a ...
formed a ridge of ice on the upper surface of its wings, eventually causing the aircraft's autopilot to suddenly disconnect and the pilots to lose control. The ATR disintegrated on impact with a field below; all passengers and crew were killed.
See also
* Black ice
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 level ...
* Freezing drizzle
Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ.
Formation
Although freezing drizzle and freezing rain are similar in that they both involve liquid precipitation a ...
* Hail
Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), 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 fal ...
* Ice pellets
Ice pellets are a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel ("soft hail") which is made of frosty white opaque rime, and from a mixture of rain and snow which is a slushy ...
* 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. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least of ice on e ...
* Icing conditions
In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Ice accretion and accumulation can affect the external surfaces of an aircraft – in which case it is referred to as ''airframe ...
* 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 ...
References
External links
Graphic Explanation
{{DEFAULTSORT:Freezing Rain
Precipitation
Weather hazards
Snow or ice weather phenomena
Road hazards