Ali Richards, of Wairakei Primary School, asks :-

How is the weather predicted?

Paul Gorman, a former weather forecaster working in the External Relations Department at the University of Canterbury, responded.

In the same way that your doctor cannot tell what's wrong with you without knowing the symptoms of your illness, weather forecasters cannot make accurate predictions without knowing what the weather is doing now.

Observations of wind speed and wind direction, clouds, temperature, rainfall and air pressure from the Earth's surface up to 10km or more above sea level are the raw ingredients for weather forecasts. These readings are fed into giant computers, some of which are the largest in the world, which then use complex mathematics to work out the likely movement and development of weather systems and plot them on maps for certain set times in the future.

Armed with several computer models from different forecasting offices around the world, forecasters decide which set of maps looks the most likely to come true. Forecasters then turn into detectives and interpret the chosen maps, satellite photographs from space of cloud patterns and weather radar images of areas of rain, hail or snow before writing their forecasts for different parts of the country. Often forecasters need to use common sense and their experience of weather conditions to help them make up their minds.

Weather forecasts in New Zealand for the next couple of days are generally accurate eight times or more out of ten but get less accurate looking more than three days ahead.