Sleet and Freezing Rain
Sleet forms when a partially melted snowflake or raindrop turns back into ice as it is falling through the air. Sleet starts out in a cloud as a snowflake or a raindrop. It may be a snowflake or a raindrop, depending on the temperature of the layer of air where it is in the sky. The snowflake or raindrop travels downwards through a much warmer layer of air. The snowflake starts to melt in this layer. As the raindrop and the melted snowflake continue their journey, they come to the last layer. This is a cold layer that makes the raindrop freeze and the snowflake refreeze. Sleet is usually tiny clear ice pellets that bounce when they hit the ground. These ice pellets are smaller than hail. Freezing Rain happens when raindrops fall in liquid form and immediately freeze as they hit a cold surface. The journey of freezing rain is like the journey for sleet, except that freezing rain travels through a much larger warmer layer than sleet. This means that the snowflake melts to form a raindrop. The last layer that the melted snowflake and the raindrop travel through is a very small cold layer. This cold layer makes the melted snowflake and raindrop very cold, but they don’t freeze. The melted snowflake and the raindrop end their journey when they hit the surface and freeze. Both the raindrop and the melted snowflake freeze because their temperatures are very cold, and the surface is very cold. Freezing rain can cause roads to be slippery like ice skating rinks. The ice that forms on trees can get so heavy and thick that the branches break off of the tree. | |
Sleet and Freezing Rain |
Sleet forms when a partially melted snowflake or raindrop turns back into ice as it is falling through the air. Sleet starts out in the clouds as a snowflake or a raindrop. If it starts out as a snowflake, this means the layer it starts out in has a below freezing temperature; if it starts out as a raindrop then the first layer has an above freezing temperature. As the snowflake or raindrop falls towards the ground, it then moves through a warmer above freezing layer. This layer causes the snowflake to start to melt. Next the raindrop and the melted snowflake travel through a colder layer which is below freezing; this last layer causes the raindrop to freeze and the melted snowflake to refreeze. Sleet is usually tiny clear ice pellets that bounce when they hit the ground. An ice pellet is about 0.2 inches (5mm) or less, which is smaller than hail. Freezing Rain happens when raindrops fall in liquid form and immediately freeze as they hit a cold surface. The process for freezing rain is similar to the process for sleet, except that freezing rain goes through a deeper layer of above freezing temperatures, allowing the snowflake to melt even further. The last layer the raindrop and melted snowflake travel through is rather small, unlike the last layer sleet travels through. This small layer causes the raindrops to become extremely cold. In this case, the ground level will have been below freezing for at least few hours if not several days. Freezing drizzle is similar to freezing rain but is much smaller and always starts out as a raindrop. Freezing rain causes highways or roadways to be like ice skating rinks for automobiles. Since freezing rain freezes on contact with a surface, over time the amount of ice on an object increases. This can cause extensive damage to trees and power lines because the weight of the ice is too heavy for these objects. In January 1998 an ice storm or freezing rain storm hit northern New England and Canada and left millions of people without power in their homes. | |
Sleet and Freezing Rain |
Sleet forms when a partially melted snowflake or raindrop turns back into ice as it is falling through the air. This happens when there are different layers of air beneath the cloud and these layers have different temperatures. In this case, if sleet started out as a snowflake, the layer right below the cloud was a cold (below freezing) layer of air. If the sleet started out as a raindrop, the layer of air below the cloud was warm (above freezing). As the raindrop or snowflake falls through the clouds, it travels through the next layer which is above freezing. The raindrop simply stays a raindrop, but the snowflake starts to melt. This journey continues for the raindrop and melting snowflake, and they travel into the next layer of air, which has below freezing temperatures. This last layer causes the raindrop to start to freeze and the melted snowflake to refreeze. Sleet is usually tiny clear ice pellets that bounce when they hit the ground. An ice pellet is about 0.2 inches (5mm) or less, which is smaller than hail. Heavy sleet is quiet rare, but it is defined as a ground accumulation of ½ inch (12.7mm), according to the National Weather Service. Freezing Rain happens when raindrops fall in liquid form and immediately freeze as they hit a cold surface. The process for freezing rain is similar to the process for sleet except there are differences in the last two layers. Freezing rain travels through a deeper layer of above freezing temperatures than sleet. Then the last layer that the raindrop and melted snowflake travel through to create freezing rain is rather small. This small layer makes the raindrops extremely cold, thus when they hit a surface they freeze on contact. In this case, the ground level will have been below freezing for at least few hours if not several days. Freezing rain causes highways or roadways to be like ice skating rinks for automobiles. Freezing rain can create an accumulation of ice on objects on the ground. The weight of this accumulation of ice can damage branches, power lines, and telephone cables. In January 1998 an ice storm or freezing rain storm hit northern New England and Canada and left millions of people without power in their homes. Freezing Rain is classified as freezing drizzle if the diameter of the raindrops is less than 0.02 inches (0.5mm). Freezing drizzle starts out in liquid form unlike freezing rain, which starts as a raindrop or snowflake.
Last modified July 24, 2008 by Vanessa Pearce. The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer |
