Transcript weather Ch. 9.5

Chapter 9: Weather Factors
Section 5: Precipitation clouds
Precipitation

Precipitation – any form of water that falls
from clouds and reaches Earth’s surface
Precipitation
Not all clouds produce precipitation.
 For precipitation to occur, cloud droplets
or ice crystals must grow heavy enough
to fall through the air.

Types of Precipitation
Rain
 Sleet
 Freezing rain
 Snow
 Hail

Types of Precipitation

Rain – most common kind of
precipitation
◦ At least 0.5 millimeters
◦ Smaller drops of water are called drizzle.

Sleet – solid particles of ice
◦ Smaller than 5 millimeters
◦ As raindrops fall they pass through a layer of
air below 0 ºC and freeze into these ice
particles.
Types of Precipitation

Freezing rain – raindrops that freeze
when they touch a cold surface.
◦ Does not freeze in the air
◦ A thick layer of ice builds up on every surface
Types of Precipitation

Snow – Water vapor in a cloud that is
converted directly into ice crystals
◦ Snowflakes have an endless number of
different shapes and patterns all with six sides
or branches
Types of Precipitation
Hail – round pellets of ice larger than 5
millimeters in diameter
 Only forms in cumulonimbus clouds
during thunderstorms

Modifying Precipitation

Cloud Seeding – tiny crystals of silver
iodide and dry ice are sprinkled into the
clouds from airplanes.
Measuring Precipitation

Snowfall Measurement
◦ A measuring stick
◦ Melting collected snow
 Measuring the depth
 10 centimeters of snow contains about the same
amount of water as 1 centimeter of rain
Measuring Precipitation

Rain Measurement
◦ Rain Gauge – an open-ended can or tube that
collects rainfall
◦ Measured by dipping a ruler into the water or
reading a marked scale