The Various Types of Precipitation

What is the difference between the various types of precipitation? I.e. snow, sleet, freezing rain and rain

Precipitation can be divided into three types dependent on whether it falls as liquid water, liquid water that freezes on impact with the surface, or ice. Different types of precipitation can fall simultaneously. Rain is an example of liquid precipitation, freezing rain is an example of liquid that freezes on impact, and snow is an example of frozen precipitation.

Rain, and all precipitation, occurs when a portion of the atmosphere becomes saturated with water vapour (the ‘gas phase’ of water) and the water condenses. Two processes can lead to the air becoming saturated; cooling the air and adding water vapour to the air.

Freezing rain is where a droplet starts as snow, and melts as it falls through the layers of the atmosphere. This melted snowflake then hits a below freezing layer of the atmosphere near the Earth’s surface. This quickly cools the droplet, meaning that on impact with a surface it will freeze; turning into ice and coating what it hits with clear ice. The cold layer which the melted snowflake hits is thick enough to cool the drop below 0cº but not thick enough to freeze it to sleet.

Sleet is similar to freezing rain except that it freezes before it hits the Earth’s surface. A snowflake falls, enters a warm layer and melts. This melted snowflake then enters a cold layer near the surface of the Earth and freezes again. When this frozen droplet hits the Earth, it is usually in the form of ice and it does not freeze on impact.

Snow, on the other hand, can only form when the atmospheric temperature is below 0cº and won’t settle if the ground temperature is above 4cº. Snow will form when the atmospheric temperature is below 0cº and when there is a minimum amount of moisture in the air. Snow is basically made up of crystals of frozen water; ice crystals have 6 points, however one snowflake can consist of multiple crystals. Snow will reach the Earth’s surface so long as it does not pass through any layers in the atmosphere that are above freezing.

Emma Barkley, 14^th February 2012

Bibliography: (All accessed 14th February 2012)

http://nsidc.org/snow/faq.html

http://www.planetpals.com/weather.html

http://ezinearticles.com/?Snow,-Sleet,-and-Freezing-Rain---Theyre-All-the-Same,-Right?&id=868391

http://www.enotes.com/science/q-and-a/what-difference-between-freezing-rain-sleet-289352