1. Weather

2. Weather is the state of the atmosphere at a specific time and place.

3. Includes such conditions as air pressure, wind, temperature and moisture in the air.

4. The Sun’s heat evaporates water into the atmosphere forming clouds; water returns to Earth as rain or snow; the Sun also heats air.

5. Temperature is a measure of air molecule movement.

6. The Sun’s energy causes air molecules to move rapidly; temperatures are high and it feels warm

7. When less of the Sun’s energy reaches air molecules, they move less rapidly and it feels cold.

8. Wind –air moving in a specific direction.

9. As the Sun heats air, it expands, becomes less dense, rises, and has low atmospheric pressure.

10. Cooler air is denser and sinks, causing high atmospheric pressure.

12. Air moves from high pressure areas to low pressure areas, causing wind.

13. Humidity –the amount of water vapor in the air.

14. Warmer air can hold more water vapor, tending to make it more humid.

15. Relative humidity –the amount of water vapor in the air compared to what it can hold at a specific temperature.

16. When air cools, it can’t hold as much water vapor, so the water vapor condenses to a liquid or forms ice crystals.

17. Dew point- the temperature at which air is saturated and condensation forms.

18. Clouds form as warm air is forced upward and cools. then the water vapor condenses in tiny droplets that remain suspended in the air.

19. The shape and height of clouds vary with temperature, pressure and the water vapor in the atmosphere.

24. Nimbus clouds are dark and so full of water that sunlight can’t penetrate them.

25. Precipitation: water falling from clouds.

26. When water droplets in clouds combine and grow large enough precipitation falls to Earth.

27. Air temperature determines whether droplets form rain, snow, sleet, or hail.

28. Section 2: Weather Patterns

29. Because air and moisture move in the atmosphere, weather constantly changes.

30. Air mass –large body of air with properties like the part of Earth’s surface over which it is formed.

34. Front –a boundary between two different air masses.

35. Clouds, precipitation, and storms occur at frontal boundaries.

36. Cold front- where colder air advances under warm air.

37. Warm front –where warmer air advances over colder air

38. Occluded front –involves three air masses of different temperatures.

40. Thunderstorms occur inside warm, moist air masses and fronts.

42. Thunder –lighting superheats the air, causing it to expand rapidly and then contract, forming sound waves.

43. Tornado –a violent, whirling wind that moves in a narrow path over land.

44. Hurricane –a large, swirling, low-pressure system that forms over tropical oceans .

45. Blizzard – a winter snow storm with strong winds, cold temperatures, and low visibility, that lasts more than three hours.

47. Section 3: Weather Forecasts

48. Meteorologists study and predict the weather.

49. The National Weather Service makes weather maps.

50. Station models show weather conditions at a specific location.