1. How can weather
be predicted?
Grade 4

2. Have you ever
wondered why the
weather changes?

3. When a large body of air moves
it causes weather changes.
Air mass
Large body of air.

4. Air masses
can be:
Hot air mass Cold air mass
All of an air mass has the same
temperature and same amount of
moisture level (amount of water in
the air).

5. Blue arrows are cold air masses
Red arrows are hot air masses

6. Temperature and moisture level depend on
where the air masses where formed.
Dry air
mass
Formed
over land
Wet air mass
Formed over
oceans or
seas
Hot air
mass
Come from
the south
Cold air
mass
Come from
the north

8. Type of weather caused by different air
masses:
Cold, dry
air masses
Cool
weather, with
little or no
precipitation
Warm, moist
air masses
Lot of
precipitation
Warm, dry
air masses
Warm
weather +
little or no
precipitation
Cold, Wet
air masses
Snow

9. Air masses
Stay separate
Why?
Because warm air is lighter than cold
air.
So, warm air masses are pushed
upward and cold air masses sink.

10. Air masses
move
The border between one air mass and
the other is called a front.

11. Air fronts
can be:
Hot
front
Cold
Front
Stationary
front

13. 1) Cold Front
Cold air moves under warm air.
Warm air mass moves up and cools down.
Water vapor condenses and moves up.
It might rain or thunderstorms develop along
the front
As the cold air mass moves forward the
weather becomes cooler.

15. 2) Warm Front
Warm air moves slides over cold air.
Warm fronts moves slowly.
Steady rain instead of thunderstorms.
Warm fronts are followed by clear, warm
weather.

18. 3) Stationary front
A front that stays in one place for many days
Happens when two air masses do not have
enough energy to move.
Steady rain instead of thunderstorms.
Weather along the stationary front is often
cloudy and wet
This kind of front can leave inches of snow or
cause flooding.

19. Types of
clouds

20. Stratus clouds
Occur
along
warm
fronts

21. Nimbostratus clouds
Brings
light rain
or snow

22. Cumulus clouds
Common
on
clear, war
m days.

23. Cumulonimbus clouds
(Thunderstorm clouds)
Develops
from
cumulus
clouds.

24. Cirrus clouds
Indicate
cool, fair
weather.

25. Weather
maps

26. Weather maps help
you know what the
weather is like in an
area.
Weather maps use symbols to
show the weather.

27. Weather
map
symbols

29. Many weather maps show temperatures.
The temperature can be:
Written on a map. Shown using colors.
Red (Very hot)
Orange (Warm)
Green (Cool)
Yellow (mild)
Blue (Very cold)

30. L(Low air pressure)
H(High air pressure)

31. In the USA the temperature unit is Fahrenheit (°F)

32. Read the
following
weather maps.

38. Where does all the information
on a weather map come form?
Weather stations

39. Some Weather instruments
1) Barometer
Measures air pressure

40. 2) Thermometer
Measures air temperature

41. 3) Wind vane
Shows which direction wind is moving

42. 4) Anemometer
Measures wind speed

43. 5) Rain gauge
Measures amount of precipitation