1. Starter Complete the Relative Humidity and Dew Point Table from yesterday with your partner. You will have 10 minutes!

2. Objectives p. 44 Today, you will be able to: Describe how clouds are classified. Compare and contrast clouds and fogs. Explain what must happen for precipitation to form. Identify what controls the type of precipitation that reaches Earth’s surface.

3. Vocabulary (Index Cards) 274. Front 275. Cirrus 276. Cumulus 277. Stratus 278. Bergeron process 279. Supercooled water 280. Supersaturated air 281. Collision-coalescence process

4. 18.2 Cloud Formation  When air is allowed to expand it cools and when it is compressed it warms  Can of air duster  cools  Pumping up a bicycle tire  warms

5. Fronts 18.2 Cloud Formation  A front is the boundary between two adjoining air masses that have contrasting characteristics http://research.utep.edu/Portals/72/weathe r%20NOAA/fronts%20vert.GIF http://www.windows2universe.org/earth/Atmosphere/i mages/cloudformation_Fronts_small.jpg http://library.thinkquest.org/C012 5863/weather/image/front_statio nary_en.gif http://mszscience.info/8_mt_rev/ of.jpg

6. Condensation 18.2 Cloud Formation  For any form of condensation to occur, the air MUST be SATURATED. Generally, there must be a surface for water vapor to condense on.  Types of Surfaces

7. Types of Clouds 18.3 Cloud Types and Precipitation  Clouds are classified on the basis of their form and height. Cirrus (cirrus = curl of hair) are clouds that are high, white, and thin. Cumulus (cumulus = a pile) are clouds that consist of rounded individual cloud masses. Stratus (stratus = a layer) are clouds best described as sheets or layers that cover much or all of the sky.

8. Basic Cloud Types http://upload.wikimedia.org/wikipedia/com mons/thumb/7/73/Cirrus_clouds2.jpg/250p x-Cirrus_clouds2.jpg http://weather.thefuntimesguide.com/imag es/blogs/fair-weather-cumulus-photo-by- see-it.jpg http://upload.wikimedia.org/wikipedia/c ommons/thumb/d/d1/Stratus-Opacus- Uniformis.jpg/300px-Stratus-Opacus- Uniformis.jpg Cirrus Cumulus Stratus

9. Types of Clouds 18.3 Cloud Types and Precipitation  High Clouds Cirrus clouds are high, white, and thin. Cirrostratus clouds are flat layers of clouds. Cirrocumulus clouds consist of fluffy masses.  Middle Clouds Altostratus clouds create a uniform white to gray sheet covering the sky with the sun or moon visible as a bright spot. Altocumulus clouds are composed of rounded masses that differ from cirrocumulus clouds in that altocumulus clouds are larger and denser.

10. Types of Clouds 18.3 Cloud Types and Precipitation  Low Clouds Stratus clouds are best described as sheets or layers that cover much or all of the sky. Nimbostratus clouds are the main precipitation makers. Stratocumulus clouds have a scalloped bottom that appears as long parallel rolls or broken rounded patches.

11. Cloud Classification (page 43) http://airlineworld.files.wordpress.com/2008/07/cloud_types.gif

12. Types of Clouds 18.3 Cloud Types and Precipitation  Clouds of Vertical Development Some clouds do not fit into any one of the three height categories mentioned. Such clouds have their bases in the low height range but often extend upward into the middle or high altitudes.

13. Fog 18.3 Cloud Types and Precipitation  Fog is defined as a cloud with its base at or very near the ground. As the air cools, it becomes denser and drains into low areas such as river valleys, where thick fog accumulations may occur.  Fog Caused by Cooling When cool air moves over warm water, enough moisture may evaporate from the water surface to produce saturation.  Fog Caused by Evaporation

14. How Precipitation Forms 18.3 Cloud Types and Precipitation  For precipitation to form, cloud droplets must grow in volume by roughly one million times. The Bergeron process is a theory that relates the formation of precipitation to supercooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water.  Cold Cloud Precipitation

15. The Bergeron Process

16. How Precipitation Forms 18.3 Cloud Types and Precipitation  Cold Cloud Precipitation Supercooled water is the condition of water droplets that remain in the liquid state at temperatures well below 0 o C. Supersaturated air is the condition of air that is more concentrated than is normally possible under given temperature and pressure conditions.

17. How Precipitation Forms 18.3 Cloud Types and Precipitation  Warm Cloud Precipitation The collision-coalescence process is a theory of raindrop formation in warm clouds (above 0 o C) in which large cloud droplets collide and join together with smaller droplets to form a raindrop.

18. Forms of Precipitation 18.3 Cloud Types and Precipitation  The type of precipitation that reaches Earth’s surface depends on the temperature in the lower atmosphere. In meteorology, the term rain means drops of water that fall from a cloud and have a diameter of at least 0.5 mm.  Rain and Snow At very low temperatures (when the moisture content of air is low) light fluffy snow made up of individual six-sided ice crystals forms.

19. Forms of Precipitation 18.3 Cloud Types and Precipitation Sleet is the fall of clear-to-translucent ice.  Rain and Snow Hail is produced in cumulonimbus clouds. Hailstones begin as small ice pellets that grow by collecting supercooled water droplets as they fall through a cloud.

20. Largest Recorded Hailstone

21. Identifying Cloud Types (page 43)

22. Cloud Elevation (page 43)

23. Post-Test (page 44) 1.How are clouds classified? 2.Compare and contrast clouds and fogs. 3.What must happen in order for precipitation to form? 4.What type of precipitation would fall to Earth’s surface if a thick layer of air near the ground was -8 o F?