Weather and Climate

1. Weather and Climate 7th Grade Science Weather Unit

2. Weather and Climate Overview • Weather VERSUS Climate • Weather Variables • Temperature • Humidity • Cloud Types • Precipitation • Air Masses • Types of Fronts • Pressure • Storms

3. Weather VERSUS Climate • Weather includes the daily and hourly conditions in the atmosphere. • Climate includes the average weather of an area over many years.

4. Weather Variables • Weather variables include many things like temperature, cloud coverage, and precipitation that produce our current weather conditions. • Some variables affect one another, some do not. • Can you think of two variables that influence one another?

5. Temperature • Temperature is defined as “A measure of the ability of a substance to transfer heat energy to another. The temperature of a substance is closely related to the average kinetic energy (energy of motion) of its molecules.” • Measured in degrees Celsius or Fahrenheit.

6. Humidity • Humidity is the amount of water vapor in the air. • Relative humidity is the amount of water in the air compared to how much water the air can hold at a give time. • Relative humidity can be found by using a sling psychrometer.

7. Cloud Types • Clouds are formed by droplets of water. • Luke Howard first classified clouds in 1803. • His system of classification used Latin terms such as: -cumulus = heap (puffy clouds) -cirrus = lock of hair (thin, wispy clouds) -stratus = layer (layers of clouds) -nimbo = rainy or stormy (produces precipitation)

8. Cloud Types • Low Clouds include those without an “Alto” or “Cirro”. (Ex. Stratus, Stratocumulus) • Middle Clouds include those the “Alto” as part of their name. (Ex. Altocumulus) • High Clouds include those that have “Cirro” as part of their name. (Ex. Cirrus, Cirrocumulus) • Exception to the cloud naming rule: Nimbostratus extend through more than two layers)

9. Stratus • Stratus clouds and formed when cooled air is holding as much water as possible. • These clouds appear as broad, flat clouds that appear blanket-like. • Type of precipitation:

10. Cumulus • Big, puffy clouds describe cumulus clouds. • They are caused by warm air rising. • Precipitation: NONE

11. Nimbostratus • Clouds that are in sheets or layers. • Hail, sleet, rain, or snow can fall from these clouds. • Lightning is not present.

12. Cirrus • Clouds that are “wispy” and light. These clouds forms when the weather is cold. • These clouds usually do not produce precipitation.

13. Cumulonimbus • Large, towering clouds that produce thunderstorms are called cumulonimbus. • Thunderstorms also contain lightning, rain, and strong winds.

14. Precipitation • Any form of water from a cloud is considered precipitation. • The type of precipitation depends upon the air temperature. • Cloud temperatures below 0ºC can cause snow if the air temperature as the water falls is below 0ºC. • Sleet can form if rain falling comes into contact with cold air. • Rain and Drizzlecan form if the air temperature is above 0°C. • Hail forms as raindrops are bounced back and forth. Constant freezing causes layers to form.

15. Picture of Hail

16. Air Masses • An air mass is a “large body of air with uniform temperature and humidity.” • Air takes on the characteristics of the land or water that it is over. • Examples include a cold air mass from Canada and warm moist air mass from the Gulf of Mexico. • Air masses near poles = cold; air masses near equator = warm

17. Types of Fronts • Definition of Front: A boundary between two air masses • Cold • Warm • Stationary • Occluded • Fronts usually move across the US from west to east.

18. Cold Front • A cold front occurs when cold air pushes underneath warmer air. • This pushes of the warm air up causes cumulonimbus clouds to form and heavy rains. • Cold fronts move quickly. • Following a cold front is cold, dry weather.

19. Warm Front • A warm front occurs when a warm air mass pushes into a cold air mass. • Cirrus clouds are formed as warm air is lifted. • As the warm front continues to move, gentle rain may occur if stratus clouds are present.

20. Stationary Front • A stationary front is a warm or cold front that has stopped moving. • When moving across a stationary front air temperature and winds shift. • Once the air masses begin to move again and the front advances it will become a WARM or a COLD front.

21. Occluded Front • An occluded front occurs when a cold front catches up to and overtakes a warm front. • Usually stormy weather near cold front and as the occluded front forms the winds shift dramatically.

22. http://ww2010.atmos.uiuc.edu/ High (H) Pressure • The center of a high pressure system has the highest pressure and pressure decreases as one move away from the center. • Winds move in a clockwise direction in the northern hemisphere. • Winds generally move from high to low pressure. • High pressure usually means little cloud coverage and fair weather.

23. Low (L) Pressure • The center of a low pressure system has the lowest pressure and pressure increases as one move away from the center. • Winds move in a counterclockwise direction in the northern hemisphere. • Fronts rotate around a low pressure system. • Weather can be poor with rain, storms, and even tornadoes.

24. Tornado • Tornadoes normally form when warm, humid air moving east runs into a cold front. • Tornadoes move counterclockwise in the Northern Hemisphere. • A tornado over warm water is called a waterspout. • Tornadoes rated F1 (weak) to F5 (very strong)

25. Thunderstorm • Formed when warm, moist air is lifted upward. • Cumulonimbus clouds form producing lightning and rain (and sometimes hail).

26. Lightning • Lightning is formed when water droplets moving within a cloud become electrically charged. • Usually the upper part of a cloud is positive (+), the lower part is (-). • Lightning charges between clouds or between clouds and the earth’s surface is big enough an electric discharge occurs.

27. Thunder • Lightning causes a quick and rapid expansion of air molecules. • This causes a sound, we call thunder. • Since sound waves travel more slowly than light waves, we SEE lightning and then HEAR thunder. • The closer we are to the storm, the more closely we see the lightning and hear the thunder.

28. Hurricane • A tropical cycle or a rotation like a tornado over warm, humid waters. • Hurricanes are named each year alternating men’s and women’s names. • Floods, high winds , landslides, and mudslides can accompany hurricanes. • Hurricanes are rated Category 1-5.

29. WARNING VERSUS WATCH VERSUS ADVISORY • From the National Weather Service: -WARNING: Issued when a weather event is occurring or has a high probability to occur. -WATCH: Occurs when the risk of a weather event has increased. The time and location are still uncertain. -ADVISORY: Issued for less serious occurrences. Caution should still be taken.

30. Sources • www.dictionary.com • Science Plus: Science and Technology BLUE BOOK • Pictures: -www.sciencelabs.com -scijinks.jpl.nasa.gov -www.usatoday.com -www.uwsp.edu -www.pasc.met.psu.edu -www.weather.about.com -www.physicalgeography.net -http://ww2010.atmos.uiuc.edu -www.noaa.gov -www.fema.gov -www.thinkquest.org -Hong Kong Observatory