How does snow form?

How does snow form?

High up in the atmosphere, the air temperature is very cold. The water vapour may fall as rain if the water does not freeze. However, if the air temperature is so cold that the water droplets freeze, tiny ice crystals form in the clouds. These ice crystals collide with each other in the clouds or grow delicate shapes. The ice crystals combine to form snowflakes. There may be hundreds of tiny ice crystals in a single snow flake. These snow flakes fall from the clouds to form snow on the ground.

If the air temperature is not too cold and the air is very moist, the snow flakes may grow into very large flake up to 1 or 2 centimetres across.

Every snow flake is different. However, each snow flake has 6 sides.

What is sleet?

What is sleet?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze completely. Sleet forms when partially frozen water droplets, or rainwater, in the clouds falls and freezes completely when it hits the surface of the Earth.

Like freezing rain, sleet may be dangerous because it coats roads and sidewalks with ice. Cars may not be able to stop on the slippery roads and many collisions between cars may occur. Slippery sidewalks are very difficult to walk along.

What is freezing rain?

What is freezing rain?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze. Under certain circumstances, the temperature of the water droplet may drop below the freezing temperature of water, but the water remains in the liquid state. This water is super-cooled. When super-cooled water falls to the surface of the Earth, the water freezes instantly on any surface it hits. This is called freezing rain.

Freezing rain may cause lots of damage. Trees and power lines may break under the weight of the heavy ice. Cities may have to go without electricity when major power lines are broken.

How do clouds form?

How do clouds form?

As warmer air pass over the ocean or large open lakes, the air picks up water vapour. As the air warms, it rises because warm air is less dense than cold air. As the warm air rises, the air cools and the water vapour in the air condenses to form clouds of water droplets.

Clouds that form at the surface of the Earth are known as fog.