Precipitation, moisture & clouds

3 ways precipitation can form

1. Orographic precipitation This occurs when an air mass forced to rise over a mountain range. The air becomes cooled and precipitation takes place.

2. Convectional precipitation This is brought about by rising and abrupt cooling of air that has been warmed by the extreme heat of the ground surface. The water vapour carried by the air condenses, producing heavy rain. Convectional rainfall is usually accompanied by a thunderstorm.

3. Cyclonic (frontal) precipitation This takes place at the boundary, or front, between a mass of warm air from the tropics and a mass of cold air from the poles. The water vapour in the warm air is chilled as it is pushed over the cold air and condenses to form clouds and rain.

What is a cloud? : A visible mass of condensed water droplets or ice suspended in the atmosphere

4 main types of cloud by shape

1. cumulus Latin for 'heap', to describe a puffy cloud

2. Cirrus Latin for 'curl of hair', to describe a wispy cloud

3. Stratus Latin for 'layer', to describe a sheet-like cloud

4. Nimbus Latin for 'rain', to describe a rain cloud.

Then you divide the clouds by their height in the atmosphere Name Height Composition Examples High Above 6 km Ice crystals Cirrus, cirrostratus Middle 2-6 km Water droplets Altocumulus, altostratus Low Within 2 km Nimbostratus, stratocumulus Vertical Development Variable Cumulonimbus

A few more terms to know

Wind Chill : It shows us how much colder the wind makes our skin feel. The temperature we feel is not the air temperature but our skin temperature. A person will sense that it's colder because the wind steals body heat by blowing away warm air that surrounds the skin.

Heat index : A measure that combines air temperature and humidity to show how hot it feels

What is the difference between…? Blizzard: a severe storm that lasts 3 or more hours, and brings low temperatures, strong winds and poor visibility due to blowing snow. Squall: a strong, sudden wind which generally lasts a few minutes then quickly decreases in speed. Flurry: a snowfall that suddenly stops and starts and changes rapidly in intensity; the accumulation and extent of the snow are limited.

humidity Absolute humidity: the actual amount of water vapor in the air. Relative humidity: how much water vapor there could be in the air at its current temperature. Warm air can hold more water vapor than cold air.