Chapter 9: Weather Chapter 9: Weather FactorsFactors

Section 5: Precipitation clouds

PrecipitationPrecipitationPrecipitation – any form of water that falls

from clouds and reaches Earth’s surface

PrecipitationPrecipitationNot all clouds produce

precipitation.For precipitation to occur, cloud

droplets or ice crystals must grow heavy enough to fall through the air.

Types of PrecipitationTypes of Precipitation

RainSleet Freezing rainSnowHail

Types of PrecipitationTypes 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 PrecipitationTypes 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 PrecipitationTypes 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 PrecipitationTypes of Precipitation

Hail – round pellets of ice larger than 5 millimeters in diameter

Only forms in cumulonimbus clouds during thunderstorms

Modifying PrecipitationModifying PrecipitationCloud Seeding – tiny crystals of silver

iodide and dry ice are sprinkled into the clouds from airplanes.

Measuring Precipitation 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 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