How do you read synoptic charts and weather circles?
Quick version
synoptic charts are maps which show the current weather conditions.
- isobars - lines ing areas with the same air pressure
- fronts - shown by coloured lines with shapes
- warm front - red line with semicircles
- cold front - blue line with triangles
- occluded front - purple line with triangles and semicircles
weather circles show current weather at a particular location
- temperature
- cloud cover
- wind direction
- wind speed
- precipitation
Learn in more depth
What is a synoptic chart?
A synoptic chart is a type of weather map.
It is a synopsis (summary) of current weather conditions across an area.
What can synoptic charts tell us about air pressure?
The main weather element of a synoptic chart is A measure of the force of the air on the Earth’s surface. If air is rising from the surface of the Earth, it is said to be low pressure. If air is sinking towards the surface of the Earth, it is said to be high pressure. Air pressure is measured in millibars (mb.):
- isobars - black lines ing areas with the same air pressure, usually 4 mb apart
- numbers - showing the air pressure in millibars
- words - areas are sometimes labelled as having high or low pressure, or are marked with an H or L
What can synoptic charts tell us about wind?
We can work out information about wind from the isobars:
- the closer together the isobars, the stronger the wind
- winds travel along the isobars
- winds blow anticlockwise around depressions (areas of low pressure)
- winds blow clockwise around anticyclones (areas of high pressure)
What can synoptic charts tell us about weather fronts?
When the different air masses that affect the UK meet, their differing temperatures and moisture produce weather fronts.
Weather fronts are shown by coloured lines with symbols on them:
- warms fronts are shown by red lines with semicircles
- cold fronts are shown by blue lines with triangles
- occluded fronts are shown by purple lines with alternating triangles and semicircles
Fronts move in an anticlockwise direction.
The symbols point in the direction the front is moving in.
The movement of air along fronts means they bring an increase in cloud and precipitation
- once a warm front has ed, the temperature rises as the front is followed by a sector of warm air
- once a cold front has ed, the temperature falls as the front is followed by colder air
What is a weather circle?
Synoptic charts often have weather circles shown on them. These circles describe the current weather in a given location.
A weather circle contains five types of information about the weather:
- temperature - shown as a number representing °C
- cloud cover - the amount of black shading the circle represents cloud cover in This is the measurement for cloud cover. Each okta makes up one eight of the sky and helps us to understand how much of the sky is covered in cloud.
- wind direction - the direction the tail points in shows where wind is coming from
- wind speed - the size and number of lines on the end of the tail show wind speed in This is the measurement of wind speed. One knot is roughly equivalent to one mile per hour.
- precipitation - the symbol to the bottom left of the circle shows the type and amount of precipitation, or fog or mist
The graphic below shows an example of a weather circle and the chart below show the key for reading it.
Test what you have learned
Study the weather station circles for Lerwick and Land's End. Describe, in detail, the weather conditions experienced on 5 January 2020 at both locations.
Lerwick
- rain shower
- low temperatures (6°C)
- cloudy skies (4 oktas)
- high winds (40 knots) from the west, south-west
Land's End
- drizzle
- warmer temperatures (12°C)
- cloudy skies (8 oktas)
- lighter winds (15 knots) from the south-west
The synoptic chart below describes the likely weather conditions in Glasgow (G) and Lyon (L).
Explain the weather conditions experienced at Glasgow and Lyon on 14 November 2021.
Look at the same synoptic chart now with some hints added.
Glasgow
Glasgow’s weather is very unsettled because a depression is ing. Glasgow will firstly experience dry weather conditions for a short period as it is currently in the warm sector. As the cold front moves over, thick clouds will bring heavy rain showers.
The wind will be strong because the isobars are close together. Wind direction will be south-westerly as winds blow anti-clockwise in a depression.
Lyon
Lyon’s weather is settled as it is covered by an anticyclone/ high air pressure. Lyon will be experiencing dry weather as there are no fronts. The wind will be calm/gentle as isobars are far apart.
Wind direction will be easterly as winds blow clockwise in an anticyclone. There will be low temperatures and possibly frost because it is a winter anticyclone.
Quiz
Recap what you have learned
The main weather element of a synoptic chart is air pressure:
- isobars are black lines ing areas with the same air pressure, usually 4 mb apart
- air pressure is shown in numbers in millibars and/or in words showing high (H) or low (L) pressure
Fronts show the boundaries where air masses meet
- warm front - red line with semicircles
- cold front - blue line with triangles
- occluded front - purple line with triangles and semicircles
Fronts move in an anticlockwise direction.
Weather circles show current weather at a particular location
- temperature in °C
- cloud cover in This is the measurement for cloud cover. Each okta makes up one eight of the sky and helps us to understand how much of the sky is covered in cloud.
- wind direction - tail points to where wind is blowing from
- wind speed in knots
- precipitation
BBC Weather Map
You can view the weather forecast on the BBC Weather map and toggle on features such as:
- precipitation
- cloud cover
- air pressure
- fog and mist
More on Weather systems
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