Synoptic charts

A synoptic chart is any map that summarises atmospheric conditions (temperatureTemperature: Temperature is how hot or cold something is, for example the atmosphere or the sea. Use a thermometer to see how many degrees Celsius/centigrade it is above or below freezing point (0 degrees C) ., precipitation [precipitation: Precipitation is the term given to moisture that falls from the air to the ground. In the UK, the most common form of precipitation is rain, but snow, hail, sleet, drizzle, fog, and mist are also precipitation. ], atmospheric pressureatmospheric pressure: Atmospheric pressure is the weight of air resting on the Earth's surface. Pressure is shown on a weather map with lines called isobars. Low pressure occurs when air is warm and rises. High pressure occurs when air becomes colder and sinks., wind speed and direction, and cloud coverage) over a wide area at a given time. These maps display an overview of the weather conditions that have been observed from many different weather stations, aeroplanes, balloons and satellites.

By collating the information over a wide area, meteorologists are able to observe the behaviour and movement of weather formations that might affect their local area in the future. This allows meteorologists to make more accurate weather forecasts. Charts are updated at least every six hours.

There are many different types of weather map, all drawn using internationally agreed standards and using accepted symbols that all meteorologists around the world can recognise.

Standard symbols used on weather charts

The synoptic chart below shows complete cloud cover (eight oktasokta: An okta is a unit used to express the extent of cloud cover. It is equal to one-eighth of the area of the sky.) over most of central and southern England and some drizzle or rain. Can you describe the weather conditions over the other parts of Europe shown on the map?

Synoptic chart

Weather symbols seem confusing until you look for the patterns. Note how increasing cloud cover is shown by covering more and more eighths (oktas) of the circle, and how more wind speed is shown by adding a little tail for every extra five knots of wind (just under 5mph / 8kmh) and a longer tail for ten knots (just under 10mph / 16kmh).

Similarly, once you know the symbol for rain is a black ball and snow is a star, then you know sleet will be a ball plus a star, and two or three or four balls will denote a heavier and heavier rainstorm.