1. 18.2 Cloud Formation I. Air Compression and Expansion
 A) Adiabatic Temperature Changes
• 1) When air is allowed to expand, it cools, and when it is compressed, it warms.

2. 18.2 Cloud Formation I. Air Compression and Expansion
B) Expansion and Cooling
• 1) Dry adiabatic rate- is the rate of cooling or heating that applies only to unsaturated air.
• 2) Wet adiabatic rate is the rate of adiabatic temperature change in saturated air.

3. Cloud Formation by Adiabatic Cooling
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4. 18.2 Cloud Formation II. Processes That Lift Air
 A) Four mechanisms that can cause air to rise
 1) Orographic Lifting:
• a) when mountains act as barriers to the flow of air, forcing the air to ascend.

5. 18.2 Cloud Formation II. Processes That Lift Air  B) Frontal Wedging
• 1) front= is the boundary between two adjoining air masses having contrasting characteristics.

6. Orographic Lifting and Frontal Wedging
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7. 18.2 Cloud Formation Processes That Lift Air C) Convergence
• 1) Convergence is when air flows together and rises.

8. 18.2 Cloud Formation  D) Localized Convective Lifting
• 1) occurs where unequal surface heating causes pockets of air to rise because of their buoyancy.

9. Convergence and Localized Convective Lifting
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10. 18.2 Cloud Formation III. Stability  A) Density Differences
• 1) Stable air tends to remain in its original position, while unstable air tends to rise.

11. 18.2 Cloud Formation III. Stability  B) Degrees of Stability
• 1) temperature inversion occurs in a thin layer of the atmosphere where the temp increases rather than decreases with height.

12. 18.2 Cloud Formation Stability  c) Stability and Daily Weather
• 1) When stable air is forced above the Earth’s surface, the clouds that form are widespread and have little vertical thickness compared to their horizontal dimension.

13. 18.2 Cloud Formation IV. Condensation
• A) Condensation nuclei= are tiny bits of particulate matter that serve as surfaces on which H2O vapor condenses.