2.3.5 Types of Precipitation

How do clouds produce precipitation?
A cloud must be tall enough to prevent sunlight from reaching its base to produce precipitation.

What types of clouds are likely to produce precipitation?
Nimbostratus and cumulonimbus clouds are likely to produce precipitation due to their height and structure.

What is the base of a cloud?
The base of a cloud appears dark when it is thick enough to prevent sunlight from passing through.

Why might a cloud not produce precipitation?
A cloud that is thin enough to allow sunlight through will not produce precipitation.

What is rain?
Rain consists of liquid water droplets that are heavy enough to fall to the ground. They range between 0.5mm and 5mm in size.

What is drizzle?
Drizzle is light rainfall with water droplets smaller than 0.5mm in size.

How does hail form?
Hail forms when raindrops are carried to freezing levels in cumulonimbus clouds, freeze, and then collide with supercooled water, causing repeated melting and freezing.

What conditions are required for snow to form?
Snow forms when the temperature is below freezing, causing water vapour to turn into solid crystals.

When does heaviest snowfall occur?
Heaviest snowfall occurs when warm moist air is forced to rise in orographic or frontal rainfall, as cold air holds limited moisture.

What is dew?
Dew is the deposition of water on surfaces due to radiation cooling in anticyclonic systems.

How does fog form?
Fog forms due to radiation cooling, often lifting when the sun rises. It may also lead to smog if an inversion layer traps cold air.

What is steam fog?
Steam fog forms when cold air blows over warmer water, causing evaporation and resulting condensation.

What is advection fog?
Advection fog forms when winds move towards the pole over cold seas, chilling the air below the dew point.

How can advection fog form over cold ocean currents?
Winds blowing over cold ocean currents can form advection fog as the air cools and reaches the dew point.

How does advection fog form when air passes from sea to land?
When air moves from sea onto cold land in winter, it chills below the dew point and forms advection fog.

What is hill fog?
Hill fog forms when air is forced to rise due to relief, causing condensation and fog, particularly in winter.

What can happen if advection fog is thick enough?
If advection fog is thick enough, drizzle may fall along with the fog.