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- Diamond dust – minute ice crystals that only occur under very cold and frigid conditions.
- Freezing rain – rain tat freezes on impact to create a shiny glaze.
- Ice pellets – clear ice, below 5mm (frozen raindrops)
- Sleet – melting snowflakes or a mixture of snow and rain
- Small hail – snow pellets with a thin ice coating
- Snow grains – opaque, flattened ice grains below 1mm diameter
- Snow pellets – opaque ice grains between 2 – 5mm
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Fog
"A summer fog for fair,
A winter fog for rain.
A fact most everywhere,
In valley or on plain."
Fog is formed when the air cools enough that the vapor pressure encourages condensation over evaporation. In order for the air to be cool on a summer night, the sky must be clear, so excess heat can be radiated into space. Cloudy skies act like a blanket, absorbing and reradiating the heat, keeping it in. So if it is cool enough (and clear enough) for fog to form, it will probably be clear the next day. Winter fog is the result of two entirely different circumstances. Above the ocean or a large lake, air is typically more humid than above land. When the humid air moves over cold land, it will form fog and precipitation. (To the east of the North American Great Lakes, this is a common phenomenon, and is known as the "lake effect"). In northerly climates, ice fog may form when the temperature drops substantially below freezing. It is almost exclusively an urban phenomenon, when the air is so cold that any vapor pressure results in condensation, and additional vapor emitted by automobiles, household furnaces, and industrial plants simply accumulates as fog.