The Atmosphere
Movement in the Atmosphere
Atmospheric Stability
Localised Winds
Clouds
Fronts
Visibility and Fog
Aircraft Icing
Thunderstorms
Altimetry
Weather Reports and Forecasts
Practice Exam

Synoptic Chart Components

Synoptic charts hold more information about the weather than they might seem at first glance. To understand them better, let’s look at how they’re constructed.

Air Pressure

Imagine we have an area of high pressure (also known as an anticyclone) over Western Europe and an area of low pressure (also known as a depression) over Eastern Europe.

Isobars

Next, we draw lines along all the points that have equal air pressure. These lines are known as Isobars.

Gradient Wind

The Pressure Gradient Force tries to create wind flowing directly from high pressure to low pressure but the Coriolis effect causes the air to rotate.

This results in the air flowing along the isobars, with the air around the high pressure sinking and the air around the low pressure rising.

When the wind flows directly along the curved isobars it is known as the Gradient Wind.

You may see the Geostrophic Wind mentioned too, which is similar. The geostrophic wind flows along parallel isobars, whereas the gradient wind flows along curved isobars.

Wind Strength

Where the isobars are close together indicates a bigger change in pressure over a smaller area, meaning the Pressure Gradient Force is stronger.

A stronger Pressure Gradient Force will try to move the air from the high to the low faster, causing the wind in this area to be stronger.

Where the isobars are spread further apart the opposite happens so the wind is lighter.

Buys Ballot Law

If you stand with your back to the wind, the low pressure will always be on your left.

This rule of thumb is called Buys Ballot Law.

So from looking at a synoptic chart, we can now tell:
Where the air is rising (low pressure) or sinking (high pressure)
The rough wind direction (along the isobars)
The rough wind strength (from the isobar spacing)
Where the low pressure is from our position on Earth (using Buy Ballot’s Law)

See if you can spot these on the synoptic below:

The white and black numbers are pressure in hectopascals (hPa).