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Type
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Surface Temperatures
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Cloud Temperatures
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Other Factors
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Snow
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Generally mid 30s or colder if the atmosphere aloft is cold
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Colder than 15 degrees
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If any layer of the atmosphere below the cloud warms to more than 38 degrees or so, precipitation will usually not be snow
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|
Sleet
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Generally mid 30s or colder
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Usually colder than 15 degrees
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A warm layer of more than 38 degrees must melt all snow, then a deep cold layer below freezing below it must be present to totally refreeze the drops
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|
Freezing Rain
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32 degrees or colder
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Could be just about anything
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Warm air aloft ensures all precipitation is liquid, then a thin cold layer below freezing near the surface "supercools" the drops so they freeze when they contact a cold surface
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Hail
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Vary widely
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Partially below freezing, partially above freezing
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Precipitation is cycled through a cloud's updraft with layers of ice growing concentrically from the center. Usually associated with a strong thunderstorm updraft
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|
Graupel
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Generally 45 degrees or colder
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Mostly below freezing, with some portion colder than 15 degrees
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Precipitation forms as snow, then is rimed in layers by supercooled liquid from updrafts into showers. Usually occurs when the lower atmosphere is very unstable. Also called snow pellets
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