Weather

1. Weather Chapter 12

2. Let’s take a look at the weather picture and why we have weather!

3. LESSON 1:Describing Weather

4. http://www.nbcnews.com/news/weather/severe-weather-hits-dallas-hundreds-thousands-texas-lose-power-n216851http://www.nbcnews.com/news/weather/severe-weather-hits-dallas-hundreds-thousands-texas-lose-power-n216851 http://www.bbc.com/news/world-us-canada-29234028

5. What impact did you hear in the video? • Discuss with your teammates: • Was there anything that surprised you? • Was there a detail that stood out? • What were some of the concerns you heard? • How many people may be affected? • What might be the costs?

6. What is Weather? • State of the atmosphere at a specific time and place • Includes such conditions as air pressure, wind, temperature, and moisture in the air • Temperature is a measure of air molecule movement • Sun’s energy causes air molecules to move rapidly; temperatures are high and it feels warm • When less of the Sun’s energy reaches air molecules, they move less rapidly and it feels cold

7. What is Weather? • Energy is transferred between fast-moving molecules and slower-moving molecules Remember from Chapter 11/Lesson 2… • CONDUCTION – transfer of energy when molecules collide • CONVECTION – occurs when warm air rises and cool air sinks; it’s the transfer of heat, usually in liquids or gases

8. http://video.nationalgeographic.com/video/climate-weather-scihttp://video.nationalgeographic.com/video/climate-weather-sci

9. Water Cycle – water makes up 70% of Earth’s surface!!

10. Water Cycle Video Link • Water moves back and forth between Earth’s atmosphere and surface • Energy from the sun causes water to evaporate from the hydrosphere and rise as vapor • Sun provides water cycle’s energy • Water on the surface absorbs heat and evaporates, entering the atmosphere • Condensation – water vapor changes back into liquid • Clouds of water become heavy and water falls to Earth as precipitation • The cycle repeats itself continuously

11. Precipitation • Rain & Drizzle- most common type of precipitation. • Freezing Rain- drizzle from stratus clouds. • Freezing Rain- raindrops freeze when they hit the ground. • Sleet- raindrops that freeze before they hit the ground. Waters 3 States Video6:52

12. Precipitation • snow- as ice grows and merges into clouds they form snowflakes. • hail- is the largest type of precipitation. • Lumps or balls of ice that fall from cumulonimbus clouds in warm weather. The Sun, Water Cycle, & Climate Video2:37 The Water Cycle and Climate Change Video 15:01

14. If we were to pick one term to help explain why we have weather, what do you think would be a good word? You might pick heat or sun….but another good choice would be Convection

15. After the atmosphere is warmed by radiation and conduction, the heat is transferred throughout the atmosphere by convection. • Since warmed air has more space between the molecules, it’s less dense and rises • Cooled air is more dense and tends to sink • In general, air near the equator tends to rise and air near the poles tends to sink

16. Take a look at this!

17. Notice the band of clouds around the equator ? This is the ITCZ or inter tropical convergence zone

18. Why do you think there is this band of clouds near the equator?

19. Did you figure it out? • Warm, moist air in the tropics rises • Cold air can hold less moisture than warm air • As the moist air rises, it condenses and forms clouds!

20. Now What? • Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks. • But why is it sunny one day, and rainy the next?

21. Let’s break for a short review 1.Transfer of heat in liquids or gases_____ 2. _____ air is dense and tends to sink. 3. Band of clouds found around the equator______ 4. Cold air holds _____ moisture than warm air 5. The Coriolis effect causes the air and water to be deflected to the _____ of the equator

22. How did you do? 1.CONVECTION 2. COLD 3. ITCZ 4. LESS 5. RIGHT

23. LESSON 2:Weather Patterns

24. Pressure demonstration • Individual – list all the things you know… what did you observe? • Remember not to make assumptions • ATT – discuss what you know together • What do you think happened?

25. Think & Write about it… On the input page of your iNB write down: • What happened to the can? • Why did this occur? • Relate this to what you know about weather on Earth.

26. Let’s take another look at the weather map • Notice that there are H’s and L’s on the map • There are also blue lines with spikes and red lines with half circles • Let’s take a closer look!

27. AIR PRESSURE • Air weight that varies over Earth’s surface • Warmer air is less dense and exerts less pressure • Cooler air is more dense and exerts more pressure

28. High Pressure Areas • When cooler air sinks and is warmed, the air can hold more moisture • This usually means sunny skies • Winds tend to move clockwise around a high

29. Low Pressure Areas • When warm air rises and is cooled, the air can not hold as much moisture • Often, these areas are associated with precipitation and stormy weather • Winds tend to move counter clockwise around the low

30. So, if you see a big H on the weather map over the area you live, you can expect fair weather

31. When you see a big L in your area, there will probably be stormy weather

32. These highs and lows move or less along the jet stream and bring us our weather changes

33. Humidity • The amount of water vapor in the air • Temperature affects how much moisture is in the air - warmer air can hold more water vapor, tending to make it more humid • Relative humidity – the amount of water vapor in the air compared to what it can hold at a specific temperature • When air cools, it can’t hold as much water vapor, so the water vapor condenses to liquid or forms ice crystals • Dew point – the temperature at which air is saturated and condensation forms

34. Clouds • Form when air rises, cools to its dew point, and becomes saturated • Shape and height of clouds vary with temperature, pressure, and water vapor in atmosphere

35. Clouds • Shape • Stratus-smooth, even sheets or layers at low altitudes • Cumulus-puffy, white clouds, often with flat bases • Cirrus-high, thin, white feathery clouds made of ice crystals • Height • Cirro – high clouds • Alto – middle-elevation clouds • Strato – low clouds • Nimbus clouds are dark and so full of water that sunlight can’t penetrate them

38. Fog

39. Fog

40. Cloud Cover Symbols • You will often see the circles drawn on a weather map

41. Fronts and Air Masses • Because air and moisture move in the atmosphere, weather is constantly changing • Air pressure – measured by barometer • An air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude; properties like the part of Earth’s surface over which it formed • Fronts are boundaries separating different air masses – clouds, precipitation, and storms occur at frontal boundaries • There are four different air masses that affect the United States

42. The Air Masses • cP( continental polar) : cold, dry stable • cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface • mP( maritime polar) : cool, moist, unstable • mT( maritime tropical) : warm, moist, unstable

43. This map shows the air mass source regions and there paths

44. Warm Fronts • A warm front is warm air displacing cool air • Shallow leading edge warm air must “overrun” cold air • These are usually slow moving Widespread precipitation develops!

45. Warm Front 2.Warm Front: The zone where warm air is replacing colder air • In U.S., warm fronts usually move from southwest to northeast • Air gets more humid after a warm front moves through

46. Cold Fronts • Cold air advances into region of warm air • Intensity of precipitation greater, but short lived • Clearing conditions after front passes • Usually approaches from W or NW Temperature drops; narrow band of violent storms!

47. Cold Front 1.Cold Front: The zone where cold air is replacing warmer air • In U.S., cold fronts usually move from northwest to southeast • Air gets drier after a cold front moves through

48. Stationary Fronts • Surface positions of the front do not move • Often a region of clouds and precipitation

49. Stationary Front 3.Stationary Front: When either a cold or warm front stops moving • When the front starts moving again it returns to either being a cold or warm front

50. Occluded Fronts • Cold front overtakes warm front • Involves three air masses of different temperatures • Often found close to the low pressure center Cloudy weather with precipitation!