Hail forms when the winds in a storm called updrafts are strong enough to push through the freezing level of a storm.  If an updraft extends far above the freezing level, then raindrops and water vapor can freeze. Frozen water droplets can blow around to different parts of a storm, and accumulate more water and re-freeze many times before it is heavy enough to fall to the ground.
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Hailstone size Size Updraft Speed
in. mph
bb < 1/4 < 24
pea 1/4 24
marble 1/2 35
dime 7/10 38
penny 3/4 40
nickel 7/8 46
quarter 1 49
half dollar 1 1/4 54
walnut 1 1/2 60
golf ball 1 3/4 64
hen egg 2 69
tennis ball 2 1/2 77
baseball 2 3/4 81
tea cup 3 84
grapefruit 4 98
softball 4 1/2 103

When large hail falls with strong winds, it can become a deadly projectile. Ranchers across America tell stories about hail storms that had killed their cattle because they were trapped in an open field during a thunderstorm.

Scientists commissioned by the National Geographic television channel studying the remains of 200 people buried in Himalayas dating from the 9th century found that Giant hail apparently killed them.
   According to the Guinness Book of World Records, the heaviest hailstones on record weighed up to 2.2lb and killed 92 people in Bangladesh in 1986.

Hail near Agate Colorado tornado August 9th 2004
Jagged Hail near Agate Colorado Tornado August 9 2004

Photo on right: Aggregate hailstone. Large hailstone with smaller stones visible. Ruler shows radius of this remarkable hail stone. Diameter is approximately 6 inches - the size of a grapefruit. Credit: NOAA Photo Library, NOAA Central Library Credit: NOAA Photo Library, NOAA Central Library
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