Ice pellets(Canadian English[1]) orsleet(American English) is a form ofprecipitationconsisting of small, hard,translucentballs of ice. Ice pellets are different fromgraupel( "soft hail" ), which is made of frosty white opaquerime,and froma mixture of rain and snow,which is aslushyliquid or semisolid. Ice pellets often bounce when they hit the ground or other solid objects, and make a higher-pitched "tap" when striking objects likejackets,windshields,anddried leaves,compared to the dull splat of liquid raindrops. Pellets generally do not freeze into other solid masses unless mixed withfreezing rain.TheMETARcode for ice pellets isPL(PEbefore November 1998[2]).
Terminology
editIce pellets are known assleetin the United States, the official term used by the U.S.National Weather Service.[3]However, the termsleetrefers to amixture of rain and snowin most Commonwealth countries instead,[4]includingCanada.[5]Because of this,Environment Canadanever uses the termsleet,and uses the terms "ice pellets" or "wet snow" instead.[6]
Formation
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Ice pellets form when a layer of above-freezing air is located between 1,500 and 3,000 meters (5,000 and 10,000ft) above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of anysnowflakesfalling through the warm layer (the French term for sleet,neige fondue,literally means "melted snow" because of this). As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze before hitting the surface, so it will becomefreezing rainand freeze on the surface instead. A temperature profile showing a warm layer above the ground is most likely to be found in advance of awarm frontduring the cold season,[7]but can occasionally be found behind a passingcold front,and often with astationary front.
Effects
editIn most parts of the world, ice pellets only occur for brief periods and do not accumulate a significant and troublesome amount. However, across the easternUnited Statesand southeasternCanada,warm air flowing north from theGulf of Mexicoahead of a strongsynoptic-scalestorm system can overrun cold, dense air at the surface for many hundreds of miles for an extended period of time. In these areas, ice pellet accumulations of2–5 cm(0.8–2.0 in)are not unheard of. The effects of a significant accumulation of ice pellets are not unlike an accumulation of snow. One significant difference however is that for the same volume of snow, an equal volume of ice pellets is significantly heavier and thus more difficult to clear away. Additionally, a volume of ice pellets takes significantly longer to melt compared to an equal volume of fresh snowfall due to less surface area.
See also
editReferences
edit- ^Katherine Barber, ed. (2004).Ice pellets.Oxford University Press.ISBN9780195418163.Retrieved29 April2024.
- ^"USA and International Code Change For Ice Pellets".National Oceanic and Atmospheric Administration.Retrieved2013-09-20.
- ^"Sleet (glossary entry)".National Oceanic and Atmospheric Administration'sNational Weather Service.Retrieved2007-03-20.
- ^"sleet Meaning in the Cambridge English Dictionary".cambridge.org.
- ^"Weather Glossary".Environment Canada.10 March 2010.Retrieved2015-03-30.
Ice pellets: This is the term Canadians use to describe frozen rain drops which are five millimetres or less in diameter and bounce when they hit a hard surface. Americans call this sleet.
- ^Chris St. Clair, Canada's Weather, p. 55, Firefly Books, 2009.ISBN1-55407-338-3
- ^Weatherquestions.com.What causes ice pellets (sleet)?Retrieved on 2007-12-08.
External links
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