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

Synoptic Features

Isobars are not always circular around a high or low pressure system and some features are given their own description.


When isobars surrounding a high pressure system elongate in one direction it is called a ridge. The ridge is sometimes described as a finger pointing out of the high.

The ridge has the same stable weather as the rest of the high pressure system but the wind will turn sharply across it.

A ridge is an elongated area of a high pressure system with similar weather to an Anticyclone


Where a finger is formed by isobars surrounding a low pressure system elongating in one direction, it is called a trough.

Weather in a trough is typically unstable, with rain and thunderstorms being common. The wind will turn sharply across a trough.


Where two highs and two lows are interacting, an area of stagnation between then often forms. This is called a Col.

As there are no isobars in a col, we can say the winds will be light. Other than this, the weather in a col can vary and is influenced by the strongest high or low surrounding it.