Clouds and Cloud Formation

What is a cloud? A cloud is a collection of small water droplets or ice crystals suspended in the air. They are visible because the water droplets and ice crystals reflect light Clouds don’t always mean precipitation

Cloud Formation Clouds form when water vapor in the air condenses For Condensation: – Air must be cooled to its Dew Point – There must be a solid particle for the water vapor to condense on

Process The sun warms a water source Evaporation occurs creating warm, moist air As the warm air rises, it cools When it cools to its Dew Point and below, the water vapor in the air condenses onto tiny particles called Cloud Condensation Nuclei Cloud condensation nuclei can be smoke, dust, dirt, salt… Most clouds are composed of water droplets, but very high altitude clouds are composed of ice crystals

How do clouds form? Radiation Warm, moist air rises Air cools as it rises DEW POINT – Condensation Occurs on Nuclei Water Source Evaporation

Frontal Lifting

Orographic Lifting Prevailing winds Warm, moist air rises up slope

3 classes of clouds based on shape: Stratus Clouds- – thin and flat with undefined edges – Stratus means “layer” – Often gray – Light mist or drizzle may come from stratus clouds – Fog is a type of stratus cloud that forms near the ground

Cumulus Clouds- – Thick and puffy on top, flat on bottom – Have well defined edges and change shape rapidly – In fair-weather, they are bright and white – They can become dark and bring thunder and lightening and heavy rain – Cumulus means “heap”

Cirrus Clouds- – Appear feathery and their ends curl – They form high in the atmosphere where temperatures are very cold – They are made of ice crystals – Do not produce precipitation that reaches the Earth

Fog Forms when moist air near the ground cools to its dew point Ground Fog (Radiation Fog)- forms in low-lying areas on clear calm nights; Earth’s surface cools and moist air near the ground reaches its dew point Sea Fog (Advection Fog)- warm moist air moves over colder water and cools to its dew point Steam Fog- evaporation takes place into cold air from warmer water; the air nearest the water is warmer, and as it rises, it cools to its dew point; seen a lot in the fall as the water cools more slowly than the air