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Understanding the Weather Map
Stacey et al (2008) Key Skills in Geography 3rd Ed. Heinemann. Sydney. p64-68
The weather map shows the state of the atmosphere on a particular data and at a particular time.
The weather map is also called a synoptic map, or a synoptic chart. It shows us a synopsis of the
weather conditions at a particular time. Weather maps are compiled from thousands of weather
observations around Australia – from neighbourhood weather stations, weather buoys, and satellite
images.
The main features shown on weather maps are: Isobars
 High-pressure and low-pressure cells
 Cold and warm fronts
 Winds
 Areas with rain in the previous 24 hours
It’s your turn 1. What is weather?
2. Define ‘synopsis’.
3. Why is a weather map also called a synoptic chart?
4. What does a weather map show?
Air Pressure
Isobars are lines that join places of equal air pressure, measured by a barometer.
Isobars surround cells of high or low pressure. Variations in air pressure are one of the major reasons
for changes in weather.
When air is cooled, it becomes heavier than the surrounding air, and falls. This increases its weight
on the Earth’s surface, causing high-pressure cells.
When air is warmed, it becomes lighter than the surrounding air and tends to rise, reducing its weight
on the Earth’s surface, resulting in the formation of low-pressure cells of air.
Differences in air pressure cause air to move. Moving air causes wind. When wind blows, it moves
air that can vary from wet to dry and from hot to cold. The type of air that moves over us influences
our weather. When the air changes, weather changes.
When the isobars on a weather map are closer together, the difference in air pressure is greater, winds
are faster and stronger, and changes in our weather can be sudden and dramatic.
When the isobars on a weather map are further widely spaced, the difference in air pressure are small,
winds are light and changes in our weather are usually more gradual.
Understanding the patterns of isobars on a weather map is important. It tells
about: Differences in air pressure across the continent
 The intensity of high pressure and low pressure cells
 The speed of moving air
 The direction in which it is moving
 As a consequence, what our weather is likely to be.
It’s your turn 5. What is air pressure?
6. What causes pressure?
7. What two things happen in the centre of a low-pressure cell?
8. In which direction does air move around a low-pressure cell?
9. What two things happen in the centre of a high-pressure cell?
10. In which direction does air move around a high-pressure cell?
11. How do we know if wind will be strong or light?
ICT Challenge
Go to this site – www.weatherchannel.com.au/synoptic-charts.aspx
Look at the Australian Synoptic Charts, pause on ONE of the charts. Use the information on this
chart to respond to the following questions.
If you are experiencing difficulties with the above link, follow the web trail:Weather Channel web site  More Weather  Synoptic Charts
Include a copy of the synoptic chart in the space below.
12. Is there a low-pressure system on the synoptic chart?
13. Is there a high-pressure system on the synoptic chart?
14. Are the isobars widely spread or close together?
15. In which direction is the air blowing around ONE of the pressure cells.
16. Using the information that is presented on the synoptic chart, forecast the weather for Sydney.
17. Identify ONE other location in Australia that will experience different weather than your Sydney
forecast. Explain WHY you believe that this location will have different weather.
Air Masses and Fronts
An air mass is a large parcel of air with the same temperature and moisture. Wind moves air masses.
The direction the wind blows, and the type of air mass it moves over us, determines our weather.
If the wind blows from: the warm to hot dry interior of Australia, our weather will usually be dry and warm to hot.
 cooler ocean areas to the south of Australia, they will bring cool to cold and moist air masses
 tropical and equatorial ocean areas, they will bring warm and very moist air.
 the sea onto the land, they may bring rain.
Air masses and fronts
Cold air and warm air do not mix easily. When winds cause cold air and warm air masses to come
into contact, there is often a very distinct boundary between them, called a front. There are two main
types of fronts: Cold front forms when cold air invades warm air
 Warm front forms when warm air is forced to rise over heavier, colder air.
Weather maps show fronts because the weather associated with fronts is quite distinctive.
The Cold Front - bring change. The cold air advances into warm air, forcing the lighter warm
air to rise rapidly. Clouds form, wind speed increases and thunderstorms and heavy rains are
common.
The Warm Front - the warm air advances towards the cooler air. It is forced to rise over the
heavier slower air. A wide band of cloud may form with rain.
It’s your turn 18. What is an air mass?
19. How do air masses move?
20. How do air masses affect our weather?
ICT Challenge Review
Look at the synoptic chart that you selected in the ICT challenge.
21. Mark and label the air masses on your selected synoptic chart. What effect are they likely
to have on the weather?
22. Mark and label any fronts on your synoptic chart. What is the weather expected ahead of
the front, and behind the front?