1. WATER IN THE ATMOSPHERE I.Humidity A. Defined as water vapor or moisture in the air (from evaporation and condensation). B. The atmosphere gains moisture from the evaporation of water from oceans, lakes, rivers, soil, plants and animals.

2. WATER IN THE ATMOSPHERE II.Relative Humidity A. Defined as the percentage of moisture the air hold relative to the maximum it can hold at a certain temperature. B.Warm air can hold more moisture than cold air. C.The temperature at which water vapor in the air condenses and turns back into a liquid is called the dew point temperature.

3. WATER IN THE ATMOSPHERE III. Measuring Relative Humidity A.Meteorologists use a psychrometer to measure relative humidity. B. You must find the temperatures of the wet-bulb and dry-bulb thermometers.

4. Relative Humidity – must use a chart like this to find % of relative humidity!

5. Clouds IV. Clouds A. Form when water vapor in the atmosphere cools to dew pt. temp and condenses onto a small particles of dust or other solid particles in the air. B. Clouds are classified according to their shape and size. a. Cumulus: clouds that look like piles of cotton balls in the sky with flat bottoms. 1. Form at an altitude of 2.4 to 13.5km. 2. Usually mean fair (good) weather. 3. They may develop into cumulonimbus clouds, which are larger clouds that produce thunderstorms (and hail).

6. Clouds B. Stratus: Gray, smooth clouds that cover the whole sky and block out the sun. 1. Form at an altitude of 2.5 kilometer. 2. Light rain and drizzle are associated with stratus clouds. 3. Nimbostratus clouds bring rain or snow. 4. Stratus clouds that form low to the ground are called fog. C.Cirrus: Clouds that form at very high altitudes (wispy and feathery clouds). 1. Made of ice crystals 2. Often appear when the weather is fair, but indicate that it will rain or snow within several hours.

7. Clouds Clouds form when the water vapor in the air cools to the dew point temperature and condenses back into a liquid. The water or ice must be able to stick to a piece of dust or dirt in the air too. Determining cloud height Abbreviations Ta = surface air temperature ( 0 F) Td = dew point temperature ( 0 F) - temperature at which water vapor condenses

8. Determining Cloud Height Cloud Height = [(Ta-Td)/4.5] x 1000 EX: If the air temperature is 58 o F and the dew point is 50 o F, what is the height of the clouds? Cloud Height = [(Ta-Td)/4.5] x 1000 Cloud Height = [(58-50)/4.5) x1000 Cloud Height = 1778 ft You must write the formula, substitute in the numbers and then solve every time with units!