Synoptic charts

A synoptic chart is any map that summarises atmospheric conditions (temperatureTemperature: How hot or cold something is, for example the atmosphere or the sea., precipitationprecipitation: Moisture that falls from the air to the ground. Includes rain, snow, hail, sleet, drizzle, fog, and mist are also precipitation., wind speed and direction, atmospheric pressure [atmospheric pressure: the weight of air resting on the Earth's surface. ] and cloud coverage) over a wide area at a given time. They display an overview of the weather conditions observed from many different weather stations, aeroplanes, balloons and satellites.

By collating the information over a wide area, meteorologists can 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.

Standard symbols used on weather charts

The synoptic chart below shows complete cloud cover (eight oktasokta: 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 can 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. More wind speed is shown by adding a little tail for every extra 5 knots of wind (just under 5 mph/8 kmh) and a longer tail for 10 knots (just under 10 mph/16 kmh).

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