1. Weather

2. Definition  The result of the atmosphere trying to balance temperature and humidity

3. The State of the Atmosphere  Air Pressure  Wind  Temperature  Amount of moisture in the air

4. Water Vapor   Water in air is in the form of a gas called water vapor   Water is also found in the atmosphere as clouds and fog   Estimated total of 14 million tons in the atmosphere

5. Evaporation   Changing of a liquid to a gas   Most evaporation occurs in oceans   Water also evaporates over lakes, rivers, puddles, and wet soil   Winds carry the water vapor

6. Transpiration   Water vapor changing back into liquid water droplets   Example: Breathing (seeing your breath)   Plants give off water vapor through leaves

7. Role of Water Vapor  Humidity: amount of water in the air Is dependent on temperature  Increase in temp results in an increase in humidity  Decrease in temp results in a decrease in humidity  When air is saturated it holds all the water vapor possible at that temperature  Figure 12-7 pg. 280

8. Water Vapor Continued  Relative Humidity: amount of water vapor air holds compared to what it can hold at a specific temperature.  Capacity is 100%, but usually water vapor may be 50%  Humidity increases as temperature increases  Humidity and comfort- Figure 12-11 pg. 283

9. Dew Point   Temperature of air at which condensation takes place   Condensation- process of changing a gas to a liquid   This takes place when saturated air is cooled

10. Dew Point   Warm air holds more water vapor   Cold air holds less water vapor   Water vapor condenses, changes into liquid water   Ground cools faster, so condensation takes place causing dew

11. Dew Point

12. Clouds  Visible formations of small droplets of water or tiny crystals of ice.  Form from condensation in the atmosphere  Shape determined by how it formed

13. Steps to Cloud Formation 1. Air ascends (goes up) 2. Pressure decreases and temperature increases. 3. Air parcel cools to the dew pt. temperature. 4. Water condenses around small particles of dust, salt, and smoke.

14. Types of Clouds  Classified:  Height  Form

15. Height Classification Cirrus - high clouds, generally don’t produce precipitation.Cirrus - high clouds, generally don’t produce precipitation. Alto - middle clouds, grayish clouds, infrequent precipitation.Alto - middle clouds, grayish clouds, infrequent precipitation. Strato - low clouds, uniform layer covering much of the sky.Strato - low clouds, uniform layer covering much of the sky.

16. Cloud Forms Cumulus - puffy, white, cauliflower- likeCumulus - puffy, white, cauliflower- like Stratus - sheets or layersStratus - sheets or layers Cirrus - high, white, thin, featheryCirrus - high, white, thin, feathery Fair weather, with storm approachingFair weather, with storm approaching

17. Stratus

18. Cirrus

19. Cumulus

20. Combinations  Cirrostratus - indicates fair weather with rain in the forecast  Altostratus - produces intermittent precipitation.  Cumulus – fair weather  Cumulonimbus - heavy precipitation, lightning, thunder, hail  dark, dense, billowy  looks like huge towers with an anvil shape

21. Cirrostratus

22. Altostratus

23. Cumulus

24. Cumulonimbus

25. Precipitation   Conditions in the atmosphere vary from season to season   Precipitation is water that falls to Earth from clouds   May be a liquid or solid

26. Precipitation  Snow – falls when temperatures are below freezing  Rain – falls when temps are above freezing  Sleet – snow falls through a layer of warm air, melts and refreezes  Hail – freezes in layers around a particle of ice during thunderstorms

27. Effect of Cloud Cover  Clear skies - more heat reach’s earth’s surface leading to warmer temperatures.  Cloudy skies – sun reflected off clouds so less sun reaches earth’s surface leading to cooler temperatures.

28. Night Cloud Cover  Clear skies – heat from earth travels freely back to space resulting in cooler temperatures.  Cloudy skies – surface heat is trapped resulting in warmer temperatures.

29. Air Mass  Large body of air that has the same properties as the surface over which it develops.  Consists of the same temperature and same amount of moisture  Air masses are dependent on where they form

30. Types of Air Masses  P (polar)-cold  A (arctic)-coldest  m (maritime)-moist  T (tropical)-warm  E (equatorial)-warmest  c (continental)-dry

31. Potential Air Masses  cA – continental arctic  cP – continental polar  cT – continental tropical  mP – maritime polar  mT – maritime tropical

32. Fronts  Boundary between two masses  Identifies the leading edge of an advancing air mass  Cloudy and stormy  Travel east to west  Usually bring changes in weather

33. Warm Front  When a warm air mass advances on a cold air mass  Drizzly precipitation  Cirrus, cirrostratus, altostratus, stratus  After front passes temperatures warm-up  Slow clearing and warmer temperatures show that front has passed

34. Warm Front

35. Cold Front  When a cold air mass advances on a warm air mass  Fast moving, produces thunderstorms, heavy rain, or snow  Altocumulus, cumulonimbus  After front passes temperatures drop  Gusty winds are formed due to air pressure differences

36. Cold Front

37. Stationary Front  When neither a cold or warm air mass is advancing  Brings very little change in the weather

38. Occluded Front  When advancing cold front takes over a warm front and pushes warm air up.  Cool temperatures and lots of precipitation  Cloudy, rainy, or snowy

39. Front Symbols

40. Severe Weather  Thunderstorms with possible: hail, heavy rain, high winds etc  Tornadoes  Hurricanes  Snow storms

41. Thunderstorms  Forms in warm, moist air masses or at cold fronts  Atmosphere unstable  16 million occur each year worldwide  Results from cumulonimbus clouds

42. Accompanies T-Storms  Heavy rainfall – drops collide with others and grow larger  Electrically active  Thunder and lightning superheat, surrounding air (50,000 degrees F) air expands producing sound waves

43. Tornadoes  Violent whirling wind moving over land from SW to NE  Produces by severe thunderstorms  1% of storms  Differences in wind direction and speed create wind shear. When wind shear is tilted, rotation is produced.  Can reach speed of 500 km/hr

44. Tornadoes Continued  Nearly 800 reported annually  75% of all occur in the US in the spring and early summer  Tornado alley: TX, OK, KS, NE  Fugi intensity scale: F0 least damage, F5 most damage

45. Hurricanes  Large swirling, low pressure system that forms over tropical oceans  Wind speeds of at least 119 km/hr  Stages of development  Tropical disturbance  Tropical depression  Tropical storm  Hurricane

46. Hurricane Risks  Storm surge causes 90% of deaths  Heavy winds and low atmospheric pressure build up over ocean  Wall of water 1-8 m high and 65-160 km long  Inland flooding

47. Summary  Clouds  Forms and heights  Air Masses  Classification  Fronts  Cold, warm, stationary, occluded  Sever Weather  Tornadoes, hurricanes. thunderstorms, etc.

48. Sources  http://www.ucar.edu/learn/index.htm http://www.ucar.edu/learn/index.htm  http://ww2010.atmos.uiuc.edu/(Gh)/home.rxml http://ww2010.atmos.uiuc.edu/(Gh)/home.rxml http://ww2010.atmos.uiuc.edu/(Gh)/home.rxml  http://vathena.arc.nasa.gov/curric/weathe r/hsweathr/index.html http://vathena.arc.nasa.gov/curric/weathe r/hsweathr/index.html http://vathena.arc.nasa.gov/curric/weathe r/hsweathr/index.html  http://www.atmos.uiuc.edu/earths_atmos phere/wind.html http://www.atmos.uiuc.edu/earths_atmos phere/wind.html http://www.atmos.uiuc.edu/earths_atmos phere/wind.html  http://eo.ucar.edu/ http://eo.ucar.edu/