All About Clouds

Clouds

• For a cloud to form, there must be water vapor in the air.

• humidity- the measure of the amount of water vapor in the air.

• relative humidity- the percentage of the amount of water vapor in the air compared to the maximum amount of water the air can hold. Measured with a psychrometer.

precipitation

Forms of precipitation:

a) rain- drops of water that are at least .5 mm in diameter (mist or drizzle if smaller)

b) sleet- drops of water that freeze as they fall from the sky; sleet-ice particles that are less than 5mm in diameter

c) freezing rain- don’t freeze as they fall but freeze as they touch something cold such as tree branches or power lines.

more forms of precipitation

d) hail- round pellets of ice larger than 5 mm in diameter that form in cumulonimbus clouds; sent up and down in the cloud, freezing a new layer of ice around the hailstone.

e) snow- water vapor in a cloud is converted directly into ice crystals

What is a cloud?

• A cloud is a large collection of very tiny droplets of water or ice crystals.

• The droplets are so small and light that they can float in the air.

Why do clouds look white?

• Clouds reflect sunlight, making them white.

• Clouds reflect all the colors of the rainbow the same amount, making them appear a white color.

Why do some clouds appear gray?

• When the clouds get really thick or really high in the sky, all the light can’t travel through the cloud. This makes the cloud look gray instead of white.

• The shadows of other clouds can make some clouds appear gray also.

How are clouds formed?Clouds form when:1. warm air rises, expands and cools. 2. some of the vapor condenses onto

tiny pieces of dust because cool air can’t hold as much water as warm air.

3.A tiny droplet forms around each dust particle.

4.They become a visible cloud when billions of these droplets come together.

Various Cloud Types

• Stratus clouds- low level clouds that are thick enough to block the sun

• Cumulus clouds- low to midlevel clouds that are puffy and white

• Cirrus clouds- thin, whispy clouds that are high in the troposphere

• Nimbus clouds- bring rain; dark colored

Click here to see a video about cloud formation

• Click to view animation of precipitation over mountains:

• http://bcs.whfreeman.com/thelifewire/content/chp56/5602001.html