How do Clouds and Precipitation Form?

Cloud Formation

Clouds form when warm, humid air rises.  As the warm moist air rises through the troposphere the air pressure decreases causing the air to expand and cool.  The air will continue to rise and continue to cool until it reaches the dew point temperature.  When the air temperature is equal to the dew point moisture in the air begins to condense

CONDENSATION LEVEL IS THE ALTITUDE AT WHICH THE AIR TEMP AND DEW POINT ARE THE SAME, AND CONDENSATION BEGINS

For water to condense there has to be a surface for the water to form on.  In the troposphere when the moisture contained in the air condenses it forms tiny droplets on the surfaces of atmospheric dust particles called condensation nuclei.

CONDESNATION NUCLEI ARE TINY PARTICLES OF DUST OR POLLEN THAT PROVIDE A SURFACE FOR WATER TO CONDENSE ON IN THE ATMOSPHERE.  A single cloud is made up of hundreds of millions of condensation nuclei and the water droplets condensing on them. 

Types of Clouds

Although all clouds are made from dust and water, and they all form in the same way, you will have certainly noticed that not all clouds look the same.  We classify clouds into different groups based on their altitude and appearance.

Cirrus Clouds

  • Cirrus clouds form at high altitudes
  • They appear very thin and feathery, and look like cotton balls that have been stretched out as far as possible.

 

 

 

 

Stratus Clouds

  • Stratus clouds form at lower altitudes.  
  • They develop in low, thick layers that often cover the entire sky creating cloudy overcast conditions.

 

 

Cumulus Clouds

  • Cumulus Clouds are the largest clouds that form.  
  • They develop into these tall humongous clouds when there is a great deal of hot humid air rising quickly through the atmosphere.
  •  Under these conditions the rapidly rising air causes the cloud to grow vertically.

How Does Precipitation Form?

Moisture in the air condenses around condensation nuclei all throughout the cloud.  Throughout this time these tiny droplets of water collide and combine to form larger and larger droplets.  Eventually, these droplets become too heavy to be suspended in the air and they fall to Earth as precipitation.  

PRECIPITATION IS ANY TYPE OF WATER FALLING TO THE SURFACE OF THE EARTH.P

There are many types of precipitation:

  • Snow
  • Hail
  • Sleet
  • Rain
  • Drizzle
  • etc

Why does it rain more in some places than in others?

Some places on Earth receive much more annual precipitation than others.  Two such places are the equator, and the windward side of mountains.

the Equator gets more rain

  • At the equator, massive global wind belts collide canceling each other out. 
  • This means there is very little wind moving in places near the equator. 
  • Without wind the only place for that hot equator air to go is up.  As it rises it cools, moisture condenses, and it rains. 
  • This extra rain explains why most tropical rainforests occur near the equator.

The windward side of mountains get more rain

THE WINDWARD SIDE OF A MOUNTAIN IS THE SIDE THAT GETS HIT BY THE WIND.

THE LEEWARD SIDE OF A MOUNTAIN IS THE SIDE WITHOUT WIND

  • When wind hits the side of a mountain it is forced upwards
  • As it rises the air expands, cools, and moisture condenses to form clouds
  • As it goes farther up the mountain, more and more moisture condenses, until eventually the cloud is saturated with water and precipitation happens.
  • By the time the air gets over the top of the mountain all of the moisture has been squeezed out of it, and it is cool and dry.

THE RAIN SHADOW IS THE A DRY AREA ON THE LEEWARD SIDE OF THE MOUNTAIN