1. Why Do We Have Weather?

2. Take good notes! There will be a quiz at the end of this presentation.
An Introduction
Take good notes! There will be a quiz at the end of this presentation.

3. WHY DO WE HAVE THE WEATHER ?
Just think about it!
Why is there wind? Why does it blow from one direction one day and another the next?
Why is it rainy one day and dry the next?
How come it’s cold in the winter?
How can we have hail in the summer?
What causes snow and freezing rain?
video

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

5. You might pick heat or sun….but another good choice would be
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

6. Convection is the transfer of heat, usually in gases or liquids.

7. 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

8. Take a look at this!

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

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

11. Did you figure it out? Warm, moist air in the topics rises
Cold air can hold less moisture than warm air
As the moist air rises, it condenses and forms clouds!
More on this later

12. Consequences of Rotation: the Coriolis effect

13. The Weather Highways
The rotation of the earth creates the Coriolis effect.
The Coriolis effect causes the air and water to be deflected to the right north of the equator.
This creates global weather highways
video

14. The Westerlies
Because of our latitude, most of our weather comes from the west
Looking at the weather map, what type of weather might we expect?
What type of weather might we expect in a few days?

15. 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 in the Northern hemisphereto be deflected to the _____ of the equator

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

17. Winds You’ve read about Global Winds: Trade Winds Westerlies
0-30°
Westerlies
Between 30-60°
Polar Easterlies
60-90°
The Doldrums & Horse Latitudes
Areas of weak and variable winds

18. Local Winds Land surfaces heat up faster than water surfaces
Sea Breeze:
Cool wind from water to land
Land Breeze:
Cool wind from land to sea

19. Valley Breezes Mountain Breezes:
Warm air from the valley moves upslope
During the day
Mountain Breezes:
Cool air descends from the mountains
During the night

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 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!

22. 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

23. 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

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

25. Surrounding these "highs" and "lows" are lines called isobars.
"Iso" means "equal" and a "bar" is a unit of pressure so an isobar means equal pressure.
We connect these areas of equal pressure with a line. Everywhere along each line is constant pressure.
The closer the isobars are packed together the stronger the pressure gradient is.

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

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

28. Fronts and Air Masses
An air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude
Fronts are boundaries separating different air masses
There are four different air masses that affect the United States

29. 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

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

31. Ok, now we see the difference in the air masses
Let’s look at the different fronts and their impact on weather
Can you see the four different types of fronts on the map?

32. Warm Fronts A warm front is when warm air is moving towards cold air.
The shallow leading edge of warm air must “overrun” cold air
These are usually slow moving

33. Cold Fronts Cold air is moving into a region of warm air
Intensity of precipitation greater, but short lived
Clearing conditions after front passes
Usually approaches from W or NW
animation

34. Stationary Fronts
When neither a warm or cold air mass is moving very much
Often a region of clouds

35. Occluded Fronts Cold front overtakes warm front
Often found close to the low pressure center
map

36. Ready for a little quiz? You’ll need a sheet of paper
Write your answers as we go
Here we go!

37. 1.
Winds in a low pressure system move _____ around the low

38. 2.
What type of front can be found close to point D ?

39. 3.
Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes?

40. 4.
Give the name of the air mass that would have the following characteristics:
cool, moist, unstable

41. 5. That important weather word that refers to the transfer of heat

42. 6. In general, air near the equator tend to_____ ( rise or fall )

43. 7.
It causes air and water to be deflected to the right north of the equator

44. 8. Which of the weather highways usually controls our weather

45. Warm air holds ( more or less ) moisture than cold air9.
Warm air holds ( more or less ) moisture than cold air

46. 10.
If there is a big H on the weather map where you live, would you expect fair or stormy weather

47. Let’s check the answers!
How did you do?
Let’s check the answers!

48. Answers 1. Counterclockwise 2. Cold 3. Cold 4. Maritime polar (mP)
5. Convection
6. Rise
7. Coriolis
8. Westerlies
9. More
10. Fair