Figure 16.12: Snow storm in Cleveland, Ohio. ( 46 )ground is not thick enough for the raindrop to freeze before it reaches the ground, the drop
may freeze on the ground, formingglaze. The weight of glaze covering a tree branch can
make the branch fall.
Hailforms in cumulonimbus clouds with strong updrafts. An ice particle falling through a
cloud is captured by an updraft and continues to grow as it travels around the convection
cell. When it finally becomes too heavy, it drops to the ground. Although hail is usually less
than 1 cm (about one-half inch), it’s not uncommon to find hail that is 5 to 10 cm (2 to 4
inch) in diameter (Figure16.13). The largest hailstone ever measured, 14 cm (5.5 inches) in
diameter and weighing 766 grams (27 ounces), was collected in Coffeyville, Kansas in 1970.
Lesson Summary
- Air temperature causes differences in pressure so that convection cells form.
- Air rising in a convection cell may cool enough to reach its dew point and form clouds
or precipitation if the humidity is high enough. - Clouds or fog may form if warmer air meets a colder ground surface. Air temperature
and humidity also determine what sorts of clouds and precipitation form. - These factors play a role in creating a pleasant or uncomfortable day, such as when it
might be warm and dry or hot and humid.