1. Why Do We Have
Weather?

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

3. WHY DO WE HAVE THE WEATHER ?
• 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?

4. 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

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

6. After the atmosphere is warmed by radiation (sun) 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.

7. Take a look at this!
Notice the band
of clouds around
the equator ?

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

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

10. Consequences of Rotation: The Coriolis
Effect - Video

11. The Weather Highways
Coriolis Effect
• The rotation of the earth
creates the Coriolis
effect.
• The Coriolis effect
causes the air and water
to be deflected to the
right when traveling
north of the equator.
• This creates global
weather highways

12. The Westerlies
• Because of our latitude,
most of our weather
comes from the west
• West-to-east motion of
the air masses,
• Looking at the weather
map, what type of
weather might we
expect?
• What type of weather
might we expect in a few
days?

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

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

15. Let’s Play a Game
• Weather Game

16. Cloud in a Bottle Demo
• Why does it work?
–Water molecules in the air (water vapor)
normally don’t stick together
–Pumping the bottle (high pressure) forces
molecules to stick together (compress)
–Releasing the pressure (low pressure)
allows the air to expand.
–As it expands, it cools.
–As the molecules cool and condense, they
stick together and form water droplets
(clouds)

17. Any Questions?
Important thing to know:
• Clouds don’t form in thin air, they need a
surface.
• Pollen, dust, pollution and other tiny specs in
the atmosphere are what water droplets
condense onto.

18. Cloud in a Bottle Questions
1. What things did we
need to happen to
make the cloud in
a bottle?
2. How do these
variables relate to
the conditions in
the atmosphere?
3. Why did I rotate t
the bottle to help
the experiment?
1. Decrease in pressure,
cooler temperature,
water vapor to condense
2. The atmosphere has
vapor, cooler
temperatures and varying
pressures
3. To create evaporation,
which makes a water
vapor

19. Data Table
Pumps Results
1 Pump
2 Pumps
3 Pumps
4 Pumps
5 Pumps

20. Turn In
• How did the increased pressure (pumping
air inside the bottle) affect the visibility of
a cloud?
• How did the decrease in pressure
(releasing the cork) affect the visibility of
the cloud?

21. End of Day Questions
1. Explain how clouds are formed. (2-3
sentences)
2. What type of weather is associated with a
high pressure system? Think about the
bottle with pressure and without pressure.
3. Explain what you should be doing for your
homework.
4. What affect does the Coriolis Effect have
on weather?
5. Explain how the cloud in a bottle works.

22. Quick Review
• How are clouds formed?
• What type of weather is associated with a
high pressure system?
• What type of weather is associated with a
low pressure system?
• What affect does the Coriolis Effect have
on weather?

23. 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?

25. Weather in the Troposphere
• Weather occurs in
the troposphere
• Airplanes usually
fly above the
troposphere in
the stratosphere.
• That’s why they
can fly above bad
weather.

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. High and Low Pressure - Video

28. High Pressure Areas
• When cooler air sinks
and is warmed, the
air can hold more
moisture
• This usually means
sunny skies
• descending (going down)

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
• ascending (going up)

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. High and Dry Video

33. These highs and lows move along
the jet stream and bring us our
weather changes.
• Video

34. • A fast flowing river of air found in the
atmosphere at around 12 km above the
surface of the Earth.
• They form at the boundaries of air masses
with large differences in temperature, such as
of the polar region and the warmer air to the
south.
Jet Stream

35. Jet Stream
Using: Hair Dryer, ping pong ball
• The hair dryer shoots a column of air up between
air that is also in the room.
• When I tilt the hair dryer left and right, the ping
pong ball stays in the column of air.
• Jet streams are columns of air in upper
atmosphere.
• These weather columns are like currents. These
columns of air move throughout the year.

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

37. The Air Masses - Video
• 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

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

39. What are Air Masses? - Video

40. 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?

41. Warm Fronts
• A warm front is
warm air displacing
cool air
• The leading edge
warm air must
“overrun” cold air
• These are usually
slow moving

43. 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
Video

44. Warm and Cold Fronts - Video

45. Describe Cold and Warm Fronts
• Your group should use printer paper to:
– Draw and label a cold front on the front side
of your paper.
– Draw and label a warm front on the back side
of your paper.
– Describe in your own words what happens
using words like: pushes, pressure, storms,
air masses, fronts, clouds, and more
– Color and decorate it
– Use the computer for extra information if
needed (diagrams, pictures, better
explanations)

46. High and Low Pressure Demo
Your Group Needs:
• Straw
• Book
• Ziploc bag
• Place the book over
the Ziploc bag.
• Place the straw inside
the Ziploc bag.
• Blow air into the bag.
• Bag Represents:
Cold Air System – High Pressure
• Book Represents:
Warm Air System – Low Pressure
• The cold air system pushes the warm air
system
• The warm air rises above the cold air.
• The warm air cools as it rises, which
makes the water vapor (GAS) condense
and form clouds (possible precipitation).

47. Cold Front is Moving In – 5:28
• As the warm air was pushed up (low pressure allowed it to rise),
the warm air cooled and condensed.
• The condensed water vapor (gas) caused clouds, which could not
hold as much moisture (water vapor [gas]).
• This caused rain and thunderstorms.
• What will the weather be like after the cold front passes
through?

48. Stationary Fronts
• Surface positions
of the front do
not move
• Often a region of
clouds
• Neither the cold
or the warm front
are ‘winning’.

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

50. 1.
• What causes a low
pressure system to
create clouds and
sometimes precipitation? L
L

51. 2.
• What type of
front can be
found close to
point D ?

52. 3.
• Which of these
fronts would you
expect to have
greater
precipitation,
but be short
lived as the
front passes?

53. 4.
• Give the name of
the air mass
that would have
the following
characteristics:
• cool, moist,
unstable

54. 5.
That important weather word that
refers to the transfer of heat

55. 6.
In general, air near the equator
tends to_____ ( rise or fall ).

56. 7.
________ causes air and
water to be deflected to the
right north of the equator.

57. 8.
Which of the weather highways usually
controls our weather

58. 9.
Warm air holds ( more or less )
moisture than cold air?

59. 10.
• If there is a big
H on the
weather map
where you live,
would you expect
fair or stormy
weather?
H
H

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

61. Answers
1. The low pressure allows the warm air to rise. As the
warm air rises, it cools. Water vapor cools and
condenses into clouds. Cold air can hold less moisture,
so eventually it might rain.
8. Westerlies
2. Cold front 9. More
3. Cold front 10. Fair
4. Maritime polar (mP)
5. Convection
6. Rise
7. Coriolis Effect

62. Predict the Weather Game
• Game

63. Centers
• Vocabulary