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Interpreting Data

What do pressure charts show?

Pressure charts, also known as synoptic charts, show the movement of high and low pressure systems across the country. The solid white lines are called isobars, and these connect points of constant pressure. In the Southern Hemisphere, winds blow clockwise around low pressure systems and anticlockwise around high pressure systems. Generally, the closer the isobars are together, the stronger the winds will be.

As a very rough rule, high pressure systems bring settled, stable weather, while low pressure systems bring rain or storms. However, there are many exceptions to these rules, with highs often causing gloomy, overcast conditions. Also note that the pressure charts are only showing what is going on at the surface. A very large part of weather forecasting is concerned with what is happening in the upper levels above the surface.

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