Hail and Snow Differences
What is the difference between hail and snow?
Hail and snow are formed by different processes and thus look quite
different, although both are composed of ice.
Snowflakes are composed of single or conglomerated ice
crystals, whereas hail is a ball of ice.
Snowflakes form when an ice crystal grows in very cold air
at the expense of surrounding water vapor.
By the way, there are many other shapes of ice crystals
(platelets, columns, etc.) that can form in a similar way,
but under different atmospheric conditions.
Hail usually starts as a frozen drop of water on a soil or
pollutant particle. The frozen drop is repeatedly carried aloft
and dropped by strong updrafts and down-drafts in a thunderstorm.
As the hailstone rises and falls, super-cooled water droplets
freeze to its surface, enlarging it.
Both snowflakes and hail drop from the clouds where they formed
when they become too heavy for the upward atmospheric motions
in the clouds to support them.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012