1. Cloud/Fog Ingredients
   • Water vapor is evaporated from earth's surface into air.
   • A cooling mechanism to condense the water vapor into liquid or ice. Rising air is the cooling mechanism to create clouds. Fog is formed by five different cooling mechanisms.
   • Condensation nuclei such as smoke, pollen, dust, pollution, etc. that provides a surface for vapor to condense onto.

2. Precipitation Processes
   There are two processes to create precipitation in a cloud:

   Collision-Coalescence occurs in clouds when larger liquid cloud droplets fall through the cloud and collide with smaller droplets that are either suspended in the cloud or falling more slowly than the larger droplets. Once the collision occurs, the large and small droplets coalesce (join) to create a new larger droplet. This larger droplet then repeats the process as it falls even faster through the cloud. The end result is an extremely large droplet called a raindrop leaving the cloud at the bottom.

   Bergeron Process occurs when a cloud is supercooled. A supercooled cloud is one that contains both liquid droplets and also ice crystals. The cloud temperature must be at or below freezing in order for this process to occur. Bergeron process occurs because water vapor molecules "prefer" to deposit onto an ice crystal (deposition) rather than to condense into a liquid droplet. Once water vapor begins to deposit onto the ice crystal there are two results: the ice crystals grow and cloud droplets evaporate (thus getting smaller). When the ice crystal leaves the cloud it will be large enough to be called a snowflake.

3. Precipitation Types
   Rain - must be liquid before hitting the surface and must not freeze onto surface.

   Snow - must begin as a snowflake (Bergeron) and remain a snowflake until reaching the ground. If flake melts into a drop it can never return to flake form again.

   Freezing Rain - rain that hits a below-freezing surface to form a glaze.

   Sleet - rain that freezes in the air and hits the ground as a small pellet.

4. Cloud Types
   Clouds are classified by altitude & appearance. There are four main groups of clouds: high, middle, low, and vertically-developed. Clouds can easily be indentified by knowing these five terms:

   cirr - high, ice, all white, very thin
   alto - middle, ice and/or liquid, white and grey, thin
   cumu - puffy appearance, all vertically-developed clouds begin with "cumu"
   nimb - cloud must be precipitating
   strat - cloud is spread out, most likely covers the sky

5. Fog Types
   Fog is denoted by the cooling mechanism involved. There are five main types of fog:

   Radiation Fog - occurs under clear, calm skies when infrared radiation (heat) escapes to upper atmosphere and outer space and the air is cooled to its dewpoint. Sometimes called valley fog or ground fog and is the most common fog over land in the world.

   Advection Fog - occurs when warm, humid air is cooled to its dewpoint by coming into contact with a cooler surface below. Snow, ice, and cold water are common surfaces that cause advection fog.

   Steam Fog - occurs when cooler air rests above warmer water and vapor that evaporates into the air cools to its dewpoint. Sometimes called Arctic sea smoke.

   Upslope Fog - occurs when air is forced to rise up a large slope and cools (adiabatically) to its dewpoint. Common in mountainous states.

   Frontal Fog - also knows as precipitation fog and occurs when rain drops fall into unsaturated, cooler air below. As the drops evaporate, water vapor is introduced into the cooler air. Very quickly, the vapor condenses into a small fog droplet.

Helpful Links:

Clouds & Precipitation - MUST SEE!
PSC Meteorology Cloud Boutique - MUST SEE!
Australian Severe Weather - MUST SEE!
Cloud Types
Snow Crystals Under A Microscope - Very cool!....pun intended.