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Rain and snow mixed is
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
composed of a mixture of rain and partially melted
snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...
. Unlike ice pellets, which are hard, and freezing rain, which is fluid until striking an object where it fully freezes, this precipitation is soft and translucent, but it contains some traces of ice crystals from partially fused snowflakes, also called slush. In any one location, it usually occurs briefly as a transition phase from rain to snow or vice versa, but hits the surface before fully transforming. Its METAR code is RASN or SNRA.


Terminology

This precipitation type is commonly known as sleet in most Commonwealth countries. However, the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
uses the term ''sleet'' to refer to ice pellets instead. In Ithaca, NY, the term Ithacating is used to describe precipitation made of a mix of rain and snow.


Formation

This precipitation occurs when the
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
in the lowest part of the atmosphere is slightly above the freezing point of water The depth of low-level warm air (below the freezing level) needed to melt snow falling from above to rain varies from about and depends on the mass of the flakes and the lapse rate of the melting layer. Rain and snow typically mix when the melting layer depth falls between these values as rain starts forming when in that range.


"Wintry showers" or "wintry mixes"

Wintry showers is a somewhat informal meteorological term, used primarily in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
, to refer to various mixtures of rain, graupel and snow at once. Though no "official" criteria exist for the term, in the United Kingdom the term is not used when any significant accumulation of snow on the ground takes place. It is often used when the temperature of the ground surface is above , preventing accumulation from occurring even if the air temperature near the surface is marginally below ; but even then, the falling
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
must generally have something else other than exclusively snow. In the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
, wintry mix generally refers to a mixture of freezing rain, ice pellets, and snow. In contrast to the usage in the United Kingdom, in the United States it is usually used when both air and ground temperatures are below . Additionally, it is generally used when some surface accumulation of ice and snow is expected to occur. During winter, a wide area can be affected by the multiple mixed precipitation types typical of a wintry mix during a single winter storm, as counter-clockwise winds around a storm system bring warm air northwards ahead of the system, and then bring cold air back southwards behind it. Most often, it is the region ahead of the approaching storm system which sees the wintry mix, as warm air moves northward and above retreating cold air in a warm front, causing snow to change into ice pellets, freezing rain and finally rain. The reverse transition can occur behind the departing low pressure system, though it is more common for precipitation to freeze directly from rain to snow, or for it to stop before a transition back.


See also

* Freezing rain * Ice pellets * Sleet (disambiguation) * Slush * Winter weather


References


External links


AMS Glossary
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