What are Synoptic Charts?

Synoptic Information
The synoptic information is compiled from hundreds of weather observations around Australia. To create a complete picture of the weather around the world, weather observations are taken at agreed times at weather stations worldwide. They are then plotted onto a synoptic chart.

They typically range in size from hundreds to thousands of kilometres across. The smooth, curving patterns of sea-level isobars indicate lines of equal atmospheric pressure. These lines highlight the central elements of our weather systems: Highs, Lows, and Cold Fronts.

Low-Pressure System Australia

The synoptic chart is similar to a topographical chart where it shows the variation in atmospheric pressure over the Earth’s surface.

We must remember, that it is a fairly simplistic representation of past, present, and future locations of weather systems, but it does provide an extremely useful guide.

Other obvious features are the patterns of High and Low Pressure and the barbed lines that identify Cold Fronts. The earth’s rotation causes air to flow clockwise around a Low Pressure System and anticlockwise around High Pressure Systems (this, of course, is in the Southern Hemisphere, the opposite occurs in the Northern Hemisphere).

Friction
Friction over the earth’s surface cause the winds to deflect inwards towards Low Pressure centres, and slightly outwards from High Pressure Systems.

Synoptic chart from BOM (Reproduced by permission of Bureau of Meteorology, © 2018 Commonwealth of Australia)

The distance between the isobars is directly related to the wind strength, the closer the lines, the stronger the winds. (In the Tropics where the rotation is weaker, this does not apply, therefore in this area isobars are usually replaced with streamline arrows which indicate wind and direction without directly relating to Pressure Gradient.)

Diverging and Converging Winds – copyright Jackie Parry

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