Christmas Giveaway 2023: Question 5 - Weather Fronts
Question
Surface pressure charts are handy for helping pilots predict the weather a few days in advance. They indicate where fronts and their associated areas of high or low pressure are and where they are likely to move to. What does the following symbol on a surface pressure chart represent?
- Occluded Front
- Warm Front
- Stationary Front
- Cold Front
Explanation
Surface pressure charts become relevant to pilots around four days before flying. They provide information on pressure systems and weather fronts, which can help us predict the weather (and the likelihood of being able to fly)!
There are a number of pressure symbols which can be depicted on a Surface Pressure Chart, and we've provided a summary of the main ones below:
Stationary Front
A stationary front (or quasi-stationary front) is a slow-moving boundary between two air masses. Typically, it is a front moving at a speed of less than 5 knots. Therefore, it is generally considered to be stationary and will not have notably moved from its previous position on a surface pressure chart.
Cold Front
A cold front is the leading edge of an advancing colder air mass, symbolised on a pressure chart as a blue line with triangles. The triangles point in the direction of movement of the cold air. The general characteristics of a cold front are cumuliform cloud, a sudden drop in temperature, a lower dewpoint temperature, a veering of wind direction and a falling pressure that rises once the front has passed. For pilots, a cold front may bring thunderstorm activity, violent winds, squall lines, windshear, turbulence and heavy rain or hail showers.
Warm Front
A warm front is the leading edge of an advancing warmer air mass, symbolised on a pressure chart as a red line with semi-circles. The semi-circles point in the direction of movement of the warm air. The general characteristics of a warm front are lowering stratiform clouds, increasing rain with the possibility of poor visibility and fog, falling pressure that slows down or stops, veering winds, and a rising temperature.
Occluded Front
Cold fronts tend to move faster than warm fronts, and over time, they can catch up with each other and create an 'occluded' front. This is shown on a surface pressure chart as a purple line with a purple semi-circle and triangle next to each other. Air trapped between a warm and cold front is called a 'warm sector', often bringing low clouds and patchy light rain.
Trough
Black lines with no semi-circles or triangles are called 'troughs' and mark areas where the air is particularly unstable, associated with increasing cloud and risk of precipitation.
If you'd like a brief overview of how to read a synoptic weather chart, the Met Office provides an excellent 3 minute overview of all of the key components which you can find below: