Below are some guidelines on what you should know from this unit on atmospheric moisture.

Objective 1: Identify the major factors that influence evaporation rates in the atmosphere.

As shown in the diagram above, the amount of water vapor in the air surrounding liquid water influences the rate of evaporation. Note that container A has relatively few water vapor molecules around it: low humidity. Also note the greater number of water vapor molecules leaving the liquid state: high evaporation rates. The opposite occurs with sample B!

Objective 2: Define evaporational cooling and condensational heating, and identify the effects these processes have on developing weather.

Evaporation is known as a cooling process in the atmosphere as heat is used in the transformation from liquid to vapor. Condensation involves water leaving the vapor state and entering a lower-energy liquid state, which releases heat and warms the air.

It is vital that you understand the effect these processes have on weather! For example,evaporation can cool the air temperature (much like when you step out of a swimming pool on a windy day and get chilled) and change precipitation from rain to snow. Condensation within the atmosphere releases heat so that rising air doesn't cool off as quickly, which increases its buoyancy and allows it to rise to sufficient heights to form thunderstorms.

Objective 3: Define dewpoint and its effect on parameters of temperature and instability.

Objective 4: Identify each cloud type within the 4 major categories (high; middle; low; vertical).

Objective 5: Explain the two major precipitation processes, and the temperature profiles needed for rain, freezing rain, sleet, and snow.

Note the thermal structure in the diagram above. You must know the thermal characteristics of the atmosphere that produce the different types of precipitation.

Objective 6: Describe the major sources of lift which ultimately produce clouds and precipitation.