all raindrops begin as snowflakes. They are formed in clouds that
are at least partly high enough for the air temperature to remain
below freezing. When snowflakes drift into a lower, warmer part
of the cloud, the flakes melt and become raindrops.
Like snowflakes, raindrops are not all the same size. They usually
range from about .02 inches (.05 cm) to .2 inches (.5 cm) in diameter.
The largest raindrops are the ones found during heavy rainstorms,
when people are likely to say it's raining cats and dogs. A raindrop
size can change as wind tosses it around or as it collides with
Throughout the years 1898 to 1904, Wilson Bentley not only photographed
snowflakes, but studied raindrop size as well. He filled several
pans with at least 1 inch (2.54 cm) of fine, sifted flour, placed
them outside during a storm, and found that each raindrop that landed
in the flour-filled pan formed a doughy pellet. After the pellets
dried, Bentley measured them-some were almost .25 inch (.64 cm)
in diameter. Bentley studied the raindrops from 70 different storms
and made 344 raindrop measurements.
of the least known facts about raindrops is that they are not shaped
like teardrops. Special wind experiments done in laboratories have
made it possible to suspend, or stop, raindrops in midair. Scientists
have found that raindrops are actually shaped like hamburger buns!
A heavy rainfall can change the landscape. In moist places, rain
falls fairly regularly. Floods in these areas are likely to be widespread
and tend to rise and fall slowly, because the soil and plants absorb
the rain. Desert areas, however, often have wild, rough floods.
Storms in desert areas tend to be heavy rains that last for a short
time. Because the soil has been baked dry by the sun, it is difficult
for rain to soak in quickly. Since there is little or no vegetation
to help slow water runoff and hold soil in place, rain rushes across
the land in dirt-filled, swift-moving sheets or streams. This kind
of rapidly flowing, dangerous water is called a flash flood. Flash
floods usually occur very quickly, almost without warning-
A heavy rainfall in an agricultural area may wash away good topsoil.
The faster the water flows, the more topsoil it sweeps away. Topsoil
is important because healthy crops depend on this nutrient-rich
layer of dirt to grow. Fortunately, farmers can use certain patterns
of plowing to slow down flowing water and to reduce the amount of
topsoil carried away.
rain forms when raindrops are supercooled, that is cooled below
the freezing point without turning into ice. Upon contact with a
cold surface, freezing rain immediately turns from a liquid to a
solid, covering everything under a layer of ice. Although the icy
layer becomes a sparkling winter spectacle when the sun shines on
it, ice-coated tree branches and electrical wires can be dangerous
if they become too heavy and snap. Streets and sidewalks covered
with a slippery coating of freezing rain are treacherous for traffic