1. Why Do We Have Weather?

2. 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?

3. 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

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

5. 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

6. Take a look at this!

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

8. 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

9. Hadley Cells Caused by convection currents.
Warm air near the equator rises
Cold air near the poles sinks

10. Consequences of Rotation: the Coriolis Effect

11. 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 West.
This creates global weather highways.

12. The Prevailing 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?

13. Combining Hadley Cells, the Coriolis Effect, and Prevailing Westerlies gives you...
Tradewinds:
Where do you think
they got their name?
Who were these winds
particularly important to?

14. Let’s break for a short review
Transfer of heat in liquids or gases_____
_____ air is dense and tends to sink.
Cold air holds _____ moisture than warm air
The Coriolis effect causes the air and water to be deflected to the _____ of the equator

15. How did you do?
1. CONVECTION
2. COLD
3. LESS
4. RIGHT

16. 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?

17. 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!

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

19. 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
Tornadoes and hurricanes can produce very low pressure readings.

20. 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

21. 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

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

24. 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?

25. Cold Fronts
This is the symbol for a cold front
Cold air pushes under a warm air mass. Warm air rises quickly=narrow bands of violent storms form

26. Warm Front
Warm air slides over departing cold air- large bands of precipitation form
This is the symbol on a map for a warm front

27. This is the weather map symbol for an occluded front
2 air masses merge and force warm air between them to rise quickly. Strong winds and heavy precipitation will occur

28. This is the weather map symbol for a stationary front
Warm or cold front stops moving. Light wind and precipitation may occur across the front boundary

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

30. 1.
Winds in a low pressure system move _____ around the low

31. 2.
What type of front can be found close to point D ?

32. 3.
Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes?

33. 4.
Give the name of the air mass that would have the following characteristics:
cool, moist, unstable

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

35. 6. In general, air near the equator tends to_____ ( rise or fall )

36. 7.
It causes air and water to be deflected to the right north of the equator

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

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

39. 10.
If there is a big H on the weather map where you live, would you expect fair or stormy weather

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

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