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Sleet
From Wikipedia, the free encyclopedia
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Sleet is a term used in a variety of ways to describe precipitation that is intermediate between rain and snow but distinct from hail.
In British English and in many Commonwealth countries, sleet refers to snow that has partially melted on its fall to the ground due to warmer surrounding air, yet has not completely melted into rain.[1] This mix of rain and snow does not usually accumulate on the ground. On rare occasions, however, a very shallow layer of sub-freezing air right at the ground can cause the non-frozen portion of the precipitation to freeze on contact. The result of this mix of freezing rain and snow is a dangerously invisible layer of ice popularly known as "black ice". This "black ice" derives its name from the fact that affected surfaces appear to be wet, instead of coated in a exceedingly slippery layer of ice.
The METAR code for this usage varies. If surface temperatures are above freezing, SNRA is the proper coding when snowflakes predominate, and RASN is the proper coding when raindrops predominate. If surface temperatures are below freezing, FZRA replaces RA to indicate that the liquid portion is freezing on contact.
In American usage, sleet is a form of precipitation consisting of frozen raindrops or refrozen partially melted snowflakes, also known as ice pellets.[2] These ice pellets are often mistaken for hail, but form in a different fashion whereby partially or completely melted snowflakes pass through a sub-freezing layer of air near the ground, causing them to re-freeze. The individual ice pellets formed by this process are the same size as the raindrops from which they formed, and are usually (but not always) smaller than hailstones.[3] Ice pellets often bounce when they hit the ground, and they generally do not freeze into a solid mass unless mixed with freezing rain.
The METAR code for ice pellets is PL.
- ^ Water in the atmosphere. Retrieved on 2007-03-20.
- ^ Sleet (glossary entry). Retrieved on 2007-03-20.
- ^ Hail (glossary entry). Retrieved on 2007-03-20.
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