ATMO 201 Lecture Notes - Lecture 13: Intertropical Convergence Zone, Cirrus Cloud, Nimbostratus Cloud
4 Apr 2017
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Note that raindrops can freeze on contact with cold ground while air temperature is above freezing. Road surface, grass, objects cool faster than the air and water can easily freeze. At 32 f you can still have rain. The temperature profile, once it gets above 32 f, you have to melt. Once you melt from a snowflake, you never go back. You get either sleet or freezing rain: higher up melting and the freezing again results in sleet and if it freezes back once it makes contact with the ground, it is freezing rain. Precipitation in the form of frozen spheres or irregular lumps of ice, always produced by convective clouds, ,nearly always cumulonimbus. An individual unit of hail is called a hailstone. By convention, hail has a diameter of 5 mm or more, while smaller particles of similar origin, formerly called small hail, may be classed as either ice pellets or snow pellets.
