Sleet results when the layer of subfreezing air at the surface extends upward far enough so that raindrop freezes into a little ball of ice. When sleet hits the surface, it bounces and does not coat objects with a sheet of ice. Freezing rain covers everything in a sheet of ice, creating shimmering and treacherous road conditions. Freezing rain is the precipitation type with the highest rate of accidents and death during the weather event.
The number of deaths due to accidents is larger for snow events, but that is because snow is more common than freezing rain. These ice accumulations are caused by freezing rain. Freezing rain is a result of snow falling through an above-freezing warm layer in the atmosphere above the surface of the earth, which melts the snowflakes into rain. The rain drops then move into a thin layer of below-freezing air right near the surface of the earth, allowing them to freeze on contact to the ground, trees, cars and other objects.
What kind of damage do different amounts of ice cause? Below we define the impacts of nuisance, disruptive and crippling ice storm events. Even though these lighter accumulations are considered a nuisance, travel can be extremely dangerous even with a light glazing. Open Accessibility Menu. An ice storm in centered from northern Arkansas to the Ohio Valley knocked out power to 1.
Accumulations were as much as three inches thick! This amount of ice starts to damage trees and power lines. These larger and warmer drops will release the heat in them when they freeze, which can be just enough to warm the surface they land on.
That, in turn, slows ice buildup on those surfaces. Supercooled water droplets falling from clouds will freeze much quicker because the temperature of these liquid droplets is already below freezing.
They just need to make contact with a surface to initiate the freezing process. Often what you may notice during a prolonged freezing rain event is how sneaky the ice buildup on the pavement is because the pavement will look wet and may even have some water on it, but ice is slowly building up under the thin layer of water.
Ice buildup of around a tenth of an inch will create very slippery pavement. When that buildup gets close to half an inch, then we can run into problems such as tree damage and power outages. Ice buildup puts extra weight on tree branches and power lines that can cause them to break — especially if gusty winds are occurring at the same time. In addition to these fallen branches causing damage to whatever they land on, power outages may also occur.
Ice accumulation from freezing rain does not coat the surface of objects evenly. Gravity will usually cause the rain water to run to the underside of an object before it freezes. Wind can create the same effect. In either case, the result would be a thicker coating of ice on one side of the object compared to the opposite side. You can accurately estimate the thickness of the ice with the method below. You will need a ruler and possibly a piece of paper and pencil.
Locate an ice-covered object that is out in the open. A small tree branch in the middle of the yard or clothesline is usually easiest to handle. Move to a position where you can see both the thickest and thinnest portions of ice coating the object from one side to the other. Using the ruler, measure the thickest part of the ice, from the edge of the object to the edge of the ice. Record that value on your paper.
Similarly, measure the thinest part of the ice, from the edge of the object to the edge of the ice. Add the two values together and then divide by two. The resulting value is your ice accumulation. Sleet is measured much the same way snow depth is measured.
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