Objectives

1. Explain how stability is determined. Describe the atmospheric conditions associated with stable, unstable, and conditionally unstable air.
2. Describe the process by which clouds form.
3. Discuss the two types of weather satellites used to observe clouds.
4. Describe the formation of precipitation according to the collision and coalescence process.
5. Describe the formation of precipitation according to the ice-crystal (Bergeron) process.
6. List several precipitation types and how they differ.
7. Describe the operation of several precipitation measuring instruments.

Atmospheric Stability

• Stability is a measure of the tendency of air that has been lifted or lowered to return to its original level, or equilibrium position.

• Stability is determined by comparing the temperature of a rising parcel of air to the temperature of its surroundings.

Cloud Formation

• For condensation to occur:
  • air must be saturated (cooled to dew point)
  • surface to condense on - condensation nuclei (dust, smoke etc.)
    
• rising air cools adiabatically due to expansion
• adiabatic process - temperature change without heat transfer
• once the condensation level is reached, clouds form

Precipitation Processes

• collision and coalescence process
• ice-crystal (Bergeron) process - supercooled droplets
  

Distribution of Ice and Water in a Cumulonimbus Cloud

Precipitation Types

• rain
• snow
• sleet and freezing rain
• hail

Measuring Precipitation

• standard rain gauge
• tipping bucket rain gauge
• weighing type rain gauge
• snow depth and water equivalent
• weather radar - Doppler radar

WSR-88D Doppler radar