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Sleet

Sleet is a type of winter precipitation characterized by small, translucent ice pellets, typically 1-5 mm in diameter, that bounce upon hitting the ground.^[1] These pellets form when snowflakes fall through a layer of above-freezing air, partially melting into slushy drops, before passing through a deeper layer of subfreezing air near the surface where they refreeze into solid ice.^[2] In meteorological observations, sleet is distinct from snow, which remains frozen throughout its descent, and is coded as "PL" or ice pellets in standard weather reports.^[3] The formation of sleet requires a specific vertical temperature profile in the atmosphere, often associated with warm fronts or low-pressure systems where a shallow warm layer overlies colder air at the surface.^[4] Accumulations of sleet are generally lighter than snow due to its density and tendency to compact, but even thin layers—such as a few millimeters—can render roads and walkways extremely slippery, posing significant risks to travel and outdoor activities.^[2] Heavier sleet events, though less common, may lead to ice buildup on trees and power lines, potentially causing minor structural damage similar to but typically less severe than that from freezing rain.^[5] Regionally, the term "sleet" varies in usage; in North American contexts, it strictly denotes ice pellets, while in the United Kingdom and some European meteorological practices, it often refers to a mixture of rain and partially melted snowflakes without full refreezing.^[6] There is no universally agreed international definition, which can lead to inconsistencies in weather forecasting and reporting across borders.^[7] Despite these variations, sleet remains a key element of wintry precipitation types, contributing to the diverse hazards of cold-season weather patterns.^[3]

Meteorology

Definition and regional variations

Sleet is a type of winter precipitation consisting of small, translucent ice pellets, typically ranging from 0.2 to 5 mm in diameter, that form when raindrops or partially melted snowflakes freeze into solid particles before reaching the ground.^[8] These pellets are generally transparent or translucent and bounce upon impact with surfaces due to their frozen state.^[9] In meteorological contexts, sleet is distinguished from liquid rain, which falls as water droplets, and snow, which consists of delicate ice crystals or flakes that accumulate softly.^[2] The term "sleet" exhibits significant regional variations in usage, particularly between North American and British/Commonwealth English. In the United States, as defined by the National Weather Service, sleet specifically refers to these ice pellets, emphasizing their frozen, pellet-like nature.^[2] In contrast, in the United Kingdom and other Commonwealth countries, according to the Met Office, sleet commonly denotes a mixture of rain and snow or partially melted snow that falls in a semi-liquid form, without a universally agreed international definition. Internationally, the World Meteorological Organization defines ice pellets (corresponding to sleet in North American usage) as precipitation consisting of transparent ice particles, usually spheroidal or irregular, with diameters generally less than 5 mm.^[10] The word "sleet" originates from Middle English "slete," dating back to around 1300, and is akin to Old English *slēte or related Germanic terms for hail or icy rain, initially describing mingled snow and rain precipitation.^[11] Its usage in formal meteorological contexts evolved through the centuries, with early modern references appearing in weather descriptions by the 19th century, though the term's core association with mixed or frozen precipitation has persisted since medieval times.^[12]

Formation mechanism

Sleet forms under a specific atmospheric profile characterized by a shallow elevated layer of air warmer than 0°C, typically less than 300 m (1,000 ft) thick, overlain by colder air aloft and overlying a deeper subfreezing layer (below 0°C) near the surface, often 0.75–1.5 km (2,500–5,000 feet) thick.^[13]^[5] This configuration arises from temperature inversions, where warmer air overrides colder surface air, creating the necessary layering for sleet's transformation process.^[14] The step-by-step formation begins with snowflakes or ice crystals forming in the cold upper atmosphere above the warm layer. As these particles fall through the elevated warm layer (with temperatures between 1°C and 3°C), they partially or fully melt into raindrops due to the sensible heating. Upon entering the subfreezing surface layer, the raindrops become supercooled and rapidly freeze into small, spherical ice pellets, typically 1–5 mm in diameter, before impacting the ground; in contrast, a shallower subfreezing layer (less than 600 m or 2,000 feet) results in freezing rain, where droplets remain liquid upon arrival.^[13]^[4] For a rain-snow mix variant, the warm layer may cause only partial melting of snowflakes without subsequent full refreezing, leading to a mixture of liquid and semi-frozen precipitation.^[15] Key influencing factors include sharp temperature gradients across the layers, often established by frontal systems such as warm fronts advancing over colder air masses, which lift moist air and promote the inversion structure.^[5] Inversion layers enhance stability in the warm sector, while the depth and minimum temperature of the subfreezing layer (ideally ≤ -6°C and at least 750 m or 2,500 feet thick) determine the completeness of refreezing; greater duration within this layer, influenced by its thickness and the fall speed of droplets, allows for larger ice pellet formation through extended supercooling and accretion.^[13]^[16] Observational evidence for these profiles comes from radiosonde (RAOB) launches, which measure vertical temperature and humidity structures during events, revealing the characteristic warm nose aloft and cold wedge near the surface; for instance, soundings from the Rapid Update Cycle (RUC) model or ACARS aircraft data often confirm warm layer depths under 300 m (1,000 feet) and subfreezing thicknesses exceeding 750 m during pure sleet episodes.^[13]

Distinction from other precipitation types

Sleet, consisting of small, hard ice pellets, is often confused with other forms of winter precipitation due to overlapping appearances and weather conditions, but key differences in formation outcomes, physical properties, and observational signatures allow for clear distinctions. These differentiations are critical for accurate forecasting and safety assessments, as misidentification can affect travel warnings and infrastructure preparations.^[2] Compared to freezing rain, sleet forms when snowflakes partially melt in a shallow layer of above-freezing air aloft and then fully refreeze into solid pellets while passing through a deeper subfreezing layer near the surface, resulting in translucent, bouncy ice particles that accumulate in a layer similar to snow.^[2] In contrast, freezing rain involves snowflakes melting completely into supercooled liquid droplets in a warmer layer aloft, which then freeze upon contact with subfreezing surfaces below a shallow cold layer, producing a smooth, adhering glaze of ice rather than discrete pellets.^[2] This glaze from freezing rain creates more hazardous conditions for travel and power lines due to its slippery and weight-accumulating nature, whereas sleet pellets do not adhere as strongly and pose comparatively lower risks of widespread icing.^[2] Sleet differs from graupel in both composition and texture: sleet comprises hard, transparent ice pellets derived from refrozen raindrops, while graupel—also known as soft hail—forms when supercooled water droplets riming (freeze onto) falling snowflakes, yielding soft, opaque, white balls that can be easily crushed by hand and typically measure 2–5 mm in diameter.^[17] Graupel often occurs in cooler, unstable conditions like those in spring or fall thunderstorms, whereas sleet is tied to winter stratiform precipitation with distinct warm-over-cold atmospheric layers.^[17] Unlike hail, which develops in convective thunderstorms through repeated cycles of updrafts carrying supercooled droplets to freeze in layers around ice nuclei—producing larger, spherical or irregular stones up to several centimeters in diameter with concentric rings of clear and milky ice—sleet pellets remain small (under 5 mm), uniform, and unlayered, forming solely from the refreezing of meltwater in stable winter air masses rather than turbulent updrafts.^[18] Hail typically falls in warmer seasons during severe storms, contrasting with sleet's association with cold-season events.^[18] In regions like the United States, where sleet strictly denotes pure ice pellets, it must be distinguished from a rain-snow mix (often termed "wintry mix"), which involves simultaneous or alternating falls of liquid rain and snowflakes without full refreezing, resulting in a slushy accumulation on the ground rather than distinct hard pellets.^[19] This mix lacks the uniform ice structure of sleet and is more common in marginally cold conditions. Sleet is measured and reported based on its physical properties, such as density—typically 0.8–0.9 g/cm³ for solid pellets—allowing differentiation from lighter, fluffier snow (around 0.1 g/cm³) or denser glaze ice.^[10] Diagnostic tools further aid identification: ground observations reveal sleet's hardness and transparency upon collection, while weather radar, particularly dual-polarization systems, detects sleet through moderate reflectivity echoes (around 30–40 dBZ) with low differential reflectivity (ZDR near 0 dB) and high correlation coefficients (CC > 0.97), contrasting with hail's brighter, high-reflectivity signatures (Z > 55 dBZ) and more irregular polarimetric patterns due to its size and layering.^[20] A distinct "bright band" on radar may indicate the melting layer associated with sleet production.^[20]

Effects and hazards

Sleet accumulates on the surface as a thin layer of small, hard ice pellets, typically reaching depths of up to 1–2 cm, which can compact into a slippery glaze under foot or vehicle traffic. This granular coating poses less persistent risk than glaze ice from freezing rain but still creates hazardous walking and driving conditions, particularly as it reduces visibility during ongoing storms and melts more rapidly than snow due to its density. Heavy sleet accumulations exceeding 0.5 inches (1.27 cm) are rare but can exacerbate these issues by forming a more substantial icy layer.^[21]^[4] Among its hazards, sleet contributes to road icing that leads to numerous vehicle accidents; in the United States, over 1,300 fatalities and 116,800 injuries occur annually from crashes on snowy, slushy, or icy pavements, with sleet as a factor in winter precipitation events. In aviation, sleet pellets can be ingested into jet engines during takeoff or landing in stormy conditions, potentially causing compressor stalls, blade damage, or reduced performance if not mitigated by anti-icing systems. Ecologically, sleet accumulations can weigh down and break branches on vegetation, leading to minor forest damage, though this effect is generally less severe than the glazing from freezing rain.^[22]^[23]^[24] The National Weather Service plays a key role in forecasting sleet through Winter Weather Advisories for expected accumulations that may cause travel disruptions and Winter Storm Warnings for heavier events exceeding 0.5 inches, often emphasizing mixed precipitation risks. Compared to freezing rain, sleet tends to be less disruptive overall as the pellets bounce and accumulate loosely rather than adhering as a solid coating, but combinations in storms can amplify dangers like power line failures. A notable historical example is the 1998 North American ice storm, where sleet mixed with freezing rain across Quebec, Ontario, and the northeastern U.S., contributing to widespread power outages affecting millions due to fallen trees and lines.^[25]^[21]^[26] Mitigation strategies for sleet include preemptive road treatments with salt or brine, which effectively melt the ice pellets by depressing the freezing point and preventing bonding to pavement—more straightforward than with deeper snow. Vehicle operators can enhance safety with tire chains to improve traction on compacted sleet layers, while public alerts via weather apps and National Weather Service notifications enable timely preparations like avoiding travel during peak events.^[27]^[28]

Other uses

Surname

Sleet is an English surname of topographical origin, derived from the Old Norse word sletta meaning a level field or flat meadow, which entered Old English as sleet to denote residence near such terrain.^[29] It functions as a variant of the surname Sleight, with early records appearing in Surrey and Middlesex during the 16th century, including the christening of Ales Slet in Bletchingley, Surrey, in 1540, and the marriage of Joane Sleet in Westminster, London, in 1601.^[29]^[30] The name may also draw from Old English slete, referring to icy rain, potentially linking it linguistically to the meteorological term for frozen precipitation.^[11] The surname spread to the United States and Canada through 19th-century migration, appearing in census records from 1840 onward.^[31] Globally, it is borne by approximately 1,646 individuals, with the highest incidence in the United States (654 bearers), England (480 bearers), and Egypt (397 bearers), where it shows the greatest density in England.^[32] In the U.S., about 58% of bearers identify as Black American, and 19th- and early 20th-century censuses indicate common occupations such as laborer for men (around 21-32%) and saleslady or teacher for women (22-27%).^[33]^[31]^[34] Notable bearers include Gregory M. Sleet (born 1951), a retired U.S. federal judge who served on the United States District Court for the District of Delaware from 1998 to 2018 and as Chief Judge from 2014 to 2017.^[35] Don Sleet (1938–1986) was an American jazz trumpeter recognized for his smooth tone and contributions to hard bop, notably as a member of Howard Rumsey's Lighthouse All-Stars in the late 1950s and early 1960s.^[36] David A. Sleet is a public health scientist specializing in behavioral approaches to injury prevention, who served nearly 20 years at the Centers for Disease Control and Prevention (CDC) as Associate Director for Science in the Division of Unintentional Injury Prevention.^[37] Moneta J. Sleet Jr. (1926–1996) was an American photographer who won the 1969 Pulitzer Prize for Feature Photography for his image of Coretta Scott King and her daughter at Martin Luther King Jr.'s funeral; he was a long-time staff photographer for Ebony magazine and a descendant of the founding family of the historical Sleettown community.^[38]^[39] John Sleet (c. 1480–1557) was an English landowner and member of the gentry in Yorkshire.^[40] The surname remains rare outside English-speaking regions, with notable presence in Egypt and limited elsewhere, and has significant cultural associations through figures like Moneta J. Sleet Jr. in African American history.

Geographical locations

Sleet Lake is a small lake located in the Kenora District of Ontario, Canada, at coordinates 51°58′23″N 88°20′14″W.^[41] This official geographical feature, recognized since 1947, lies within the boreal forest region and serves primarily for local recreation and fishing, though it lacks unique ecological distinctions beyond the typical northern Canadian climate.^[41] Another Sleet Lake exists on the Tuktoyaktuk Peninsula in the Northwest Territories, Canada, a glacial-origin lake amid rolling hills at approximately 69°29′N 133°49′W, surrounded by dwarf birch and other tundra vegetation.^[42] It has been studied for paleoenvironmental research, including pollen analysis that reveals Late Quaternary arctic tree-line dynamics, with evidence of ancient black spruce woodlands nearby from 8400 to 3500 years BP.^[43] The site contributes to understanding regional climate history but has no significant human population or recreational use. In the United States, Sleettown was a historical African American community in Boyle County, Kentucky, near Perryville, established post-Civil War on 96 acres and active until the 1930s.^[39] Now part of the Perryville Battlefield State Historic Site, it features the Sleettown Trail for visitors exploring its legacy, though it holds low modern population impact.^[44] No major cities, towns, or other prominent features bear the name Sleet, and naming origins for these sites may tie to local weather patterns or the Sleet surname.^[39]

References

[1]
Glossary - NOAA's National Weather Service
(PL) - Sleet is defined as pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes. These pellets of ice usually ...
[2]
What is the Difference between Sleet, Freezing Rain, and Snow?
Sleet occurs when snowflakes only partially melt when they fall through a shallow layer of warm air. · Freezing rain occurs when snowflakes descend into a warmer ...
[3]
Winter Weather Types - NOAA National Severe Storms Laboratory
Sleet occurs when snowflakes only partially melt when they fall through a shallow layer of warm air. These slushy drops refreeze as they next fall through a ...
[4]
Freezing Rain and Sleet - National Weather Service
Sleet is simply frozen raindrops and occurs when the layer of freezing air along the surface is thicker. This causes the raindrops to freeze before reaching the ...
[5]
Winter Wx
Sleet is less prevalent than freezing rain and is defined as frozen raindrops that bounce on impact with the ground or other objects. The diagram shows a ...
[6]
Rain, sleet or snow? | Royal Meteorological Society
Jan 6, 2022 · But other countries, such as the United States, use the term sleet to mean ice pellets. These form when snowflakes melt into rain and refreeze ...
[7]
https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/snow/sleet
[8]
Sleet | Precipitation, Freezing Rain, Hail - Britannica
Sleet, globular, generally transparent ice pellets that have diameters of 5 mm (0.2 inch) or less and that form as a result of the freezing of raindrops.
[9]
About NOAA/NWS Forecast Parameters, Weather Types and Hazards
Sleet, Sleet is defined as pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes. These pellets of ice usually ...
[10]
Sleet - Etymology, Origin & Meaning
Originating c. 1300 from Old English *slete, related to Germanic words for hail, sleet means precipitation of snow and rain or to rain and snow ...
[11]
sleet, n.¹ meanings, etymology and more | Oxford English Dictionary
The earliest known use of the noun sleet is in the Middle English period (1150—1500). OED's earliest evidence for sleet is from around 1300, in Land of Cokayne.
[12]
[PDF] FORECASTING WINTER PRECIPITATION TYPE
Sleet events favored over freezing rain with warm layer temp. <2°C and warm layer depth <1000 ft. If ground is frozen but air temp. is slightly above 0°C then ...
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Sleet - National Geographic Education
Oct 19, 2023 · Sleet is type of precipitation distinct from snow, hail, and freezing rain. It forms under certain weather conditions, when a temperature inversion causes snow ...Missing: international | Show results with:international
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Determining Winter Precip - National Weather Service
Unmixed (no freezing rain) sleet events usually are most probable when the average minimum temperature of the low-level subfreezing layer is colder than -5 C. ...
[15]
Observation of Ice Pellets and its Association with Meteorological ...
Mar 19, 2024 · Both episodes had smaller maximum size (1.8 mm in average) of ice pellets ... thickness of the subfreezing layer (Carmichael et al. 2011). Of all ...
[16]
What is graupel? How it is different from sleet or hail? - AccuWeather
It can be the same size as sleet but is typically white and opaque. Unlike hail or sleet, graupel is soft and can be crushed easily in your hand, and is ...
[17]
Hail Basics
### Hail Formation and Characteristics
[18]
You Say "Sleet", I Say "Snow Mixed With Rain" - AMS Weather Band
Feb 22, 2023 · Brits use the term “sleet” to refer to what people in the US and Canada call “rain mixed with snow” (or vice versa).<|separator|>
[19]
Ice Pellets | International Cloud Atlas
Ice pellets may be partly liquid. Their density is usually close to, or above, that of ice (0.92 g/cm3). « PreviousNext ». The text enclosed in grey-shaded ...
[20]
[PDF] What is Dual-Polarization Radar and What Can It Do for Me?
Theoretically, improve the accuracy of precipitation estimates, leading to better flash flood detection. (questionable at this time).
[21]
https://forecast.weather.gov/glossary.php?word=sleet%2Bwarning
[22]
Snow & Ice - FHWA Road Weather Management
Sep 6, 2024 · Each year, 24 percent of weather-related vehicle crashes occur on snowy, slushy or icy pavement and 15 percent happen during snowfall or sleet.
[23]
[PDF] AC 91-74B - Pilot Guide: Flight In Icing Conditions
Oct 8, 2015 · Aircraft icing remains a key aviation safety issue. ... Another hazard occurs when ice breaks off and is ingested into a running engine,.
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[PDF] Ice storms and forest impacts
Ice storms also damage forests in the north-west. A storm in November 1996 in eastern Washington and adjacent Idaho caused widespread tree da- mage and heavy ...
[25]
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Winter Weather Advisories are issued when snow, blowing snow, ice, sleet, or a combination of these wintry elements is expected but conditions should not be ...
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25th Anniversary of the Devastating 1998 Ice Storm in the Northeast
... Quebec and southern Ontario, around freezing along the immediate Canadian ... The depth of the sub-freezing air is not deep enough to change rain to sleet ...
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[PDF] MANUAL OF PRACTICE FOR AN EFFECTIVE ANTI-ICING ...
This manual provides information for successful implementation of an effective highway anti-icing program. It is written to guide the maintenance manager in ...
[28]
[PDF] NEW YORK STATE - nysdot
Apr 1, 2006 · Properly fit tire chains should be available for each snow and ice vehicle. Conditions such as ice storms may require the use of chains.
[29]
Sleet Surname: Meaning, Origin & Family History - SurnameDB
The derivation is from the Olde Norse word 'sletta', a level field, borrowed into Olde English as the dialectal 'sleet', meaning a flat meadow, or any level ...Missing: etymology | Show results with:etymology
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Sleet Name Meaning and Sleet Family History at FamilySearch
Sleet Name Meaning. English (Surrey and Middlesex): variant of Sleight .Missing: etymology | Show results with:etymology
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Sleet Surname Meaning & Sleet Family History at Ancestry.com®
The Sleet family name was found in the USA, the UK, Canada, and Scotland between 1840 and 1920. The most Sleet families were found in United Kingdom in 1891. In ...Missing: distribution | Show results with:distribution
[32]
Sleet Surname Origin, Meaning & Last Name History - Forebears
Learn the fascinating origin of the Sleet surname; its meaning ... Descriptions may contain details on the name's etymology, origin, ethnicity and history.
[33]
Sleet Surname/Last Name: Meaning, Origin & Family History
Regarding its ethnic identity, census data reveals that 'Sleet' is predominantly associated with the Black community, although there was a slight decrease (8.91 ...Missing: distribution | Show results with:distribution
[34]
Sleet Last Name — Surname Origins & Meanings - MyHeritage
The surname Sleet has its historical roots in England, with its earliest appearances dating back to the medieval period.Missing: distribution | Show results with:distribution
[35]
Judge Gregory M. Sleet | District of Delaware
Sleet. Judge Tabs. About(active tab); Biography. About. District Judge. Appointment Start Date: September 23, 1998. Appointment End Date: September 28, 2018.
[36]
Don Sleet Songs, Albums, Reviews, Bio & More |... - AllMusic
Although little known, Don Sleet was a gifted hard bop/post-bop trumpeter who had an attractive, smooth tone along the lines of Kenny Dorham and Art Farmer.Missing: musician | Show results with:musician
[37]
https://bizzellus.com/team-member/david-a-sleet-phd/
[38]
Sleet last name popularity, history, and meaning
The surname SLEET has its origins in the Germanic languages and is believed to have first appeared in England during the medieval period. It is thought to be ...Missing: etymology | Show results with:etymology
[39]
https://nkaa.uky.edu/nkaa/items/show/1514
[40]
North American Pollen Database - Neotoma Landing Pages
Site Name: Sleet Lake Description: Glacial origin lake. Physiography: rolling hills on Tuktoyaktuk Pininsula. Surrounding vegetation: dwarf Betula, ...
[41]
The palynological record of Late-Quaternary arctic tree-line in ...
Open woodlands with black spruce grew as far north as Sleet Lake from 8400 to 3500 yr BP. These woodlands gradually retreated to just south of Reindeer Lake ...
[42]
Sleettown (Perryville, KY)
Jun 28, 2023 · Sleettown was an African American community developed after the Civil War on 96-acres near Perryville, KY.
[43]
Explore | Perryville Battlefield State Historic Site - Kentucky Tourism
From 1865 to the 1930s, an African American community known as Sleettown thrived on the grounds of what is now Perryville Battlefield. This community included ...