Cloud Formation & Cloud Types

It's all about water and altitude

Cloud formation

A cloud is born

To understand how clouds form remember this...

1) when air is compressed it heats up

2) when air expands it cools

3) as air rises, it will expand due to decreased air pressure SO air cools as it rises

4) when air reaches its dew point, it is saturated with water and condensation occurs

5) when rising air reaches its dew point a cloud will form


  • adiabatic temperature changes: a temperature change that happens even though heat isn't added or taken away, but happen because air either expands or is compressed
  • dry adiabatic rate: rate at which unsaturated air heats or cools as its altitude changes; air will cool 10 degrees Celsius for every 1000m it goes up, and will heat 10 degrees Celsius for every 1000m it descends
  • wet adiabatic rate: rate at which saturated air heats or cools as its altitude changes; this rate is generally between 5 and 9 degrees Celsius for every 1000m the air changes in height
How clouds form

Getting air to rise

Air likes to stay where it is, BUT there are 4 ways to get it to rise...


1) orographic lifting: occurs when air hits elevated terrains (such as mountains) and is forced upwards


2) frontal wedging: occurs when warm and cold fronts collide; the warmer air is forced up over the colder, denser air


3) convergence: occurs when lower level air flows together and is pushed upwards


4) localized convective lifting: occurs when there is unequal heating of the Earth's surface, such as the difference between a parking lot and the wooded park beside it

Stable vs Unstable

Stable air tends to stay right where it is = no clouds
  • occurs when there is a gradual decrease in air temperature as altitude increases
  • a temperature inversion occurs when air temperature increases as altitude increases, this creates the most stable air


Unstable air tends to rise = clouds

  • occurs when air is warmer (less dense) than the surrounding air
  • the warm air will continue to rise until its temperature matches the air around it

How does this impact the weather?

When stable air is forced to rise...
  • relatively thin, widespread clouds are formed
  • light to moderate precipitation if any
  • dreary, overcast day with light rain = stable air rising


When unstable air rises...

  • thick, towering clouds
  • potentially heavy precipitation, thunderstorms, possible tornadoes
  • bubbly, cauliflower-shaped clouds = unstable air rising

Knowledge Check

Please get a book, turn to page 516 and answer questions 1-5. These questions are due at the end of class for a grade. You can turn them in on a piece of paper, or email them to me- your choice. Please let me know if you have questions. When you are done, please continue with the next section - Types of Clouds.

Types of Clouds

Clouds are classified based on their form and height...

There are three basic forms

1) cirrus - high, white, thin clouds with a veil-like or feather-like appearance

2) cumulus - rounded, cauliflower shaped, individual clouds usually with a flat base

3) stratus - sheets or layers of clouds that cover most if not all of the sky

  • all clouds reflect one of these three forms or are combinations or modifications of them


There are three levels of cloud heights

1) high: cloud bases are above 6000m

  • cirrus, cirrostratus and cirrocumulus clouds are found at this level; these cloud types are not precipitation producers

2) middle: cloud bases are often 2000m to 6000m

  • altocumulus and altostratus clouds are found at this level; these cloud types may produce infrequent, light precipitation

3) low: cloud bases are below 2000m

  • stratus, stratocumulus and nimbostratus clouds are found at this level; these cloud types may produce light precipitation, however, nimbostratus clouds are one of the main rain producers

- fog occurs when the base of a cloud is on or very near the ground; can be caused by cooling air or by evaporation

Weather 101: A Tutorial on Cloud Types

Knowledge Check

Please get a book, turn to page 522 and answer questions 1, 2 & 6. These questions are due at the end of class for a grade. You can turn them in on a piece of paper, or email them to me- your choice. Please let me know if you have questions.