A seasonal prediction aims to estimate the change in the likelihood of a climatic event happening in the coming months. It is a forecast of the possible conditions averaged over a large region (e.g. country-wide) and over a specified period of time (e.g. three months). Specifically, the seasonal prediction gives an indication of the possible conditions over the UK for the coming 3-month period.
It does not indicate that these average conditions will prevail continuously, as the period is likely to contain a range of different types of weather. Nor does it indicate that these average conditions will be the same over the whole region. The questions we can answer in seasonal forecasting are different to the questions we are trying to answer in weather forecasting. For example, in seasonal forecasting we try to address questions like:
As you can see, in both these questions there is a comparison with an average value which is usually calculated from observations. So, in seasonal forecasting we are trying to estimate the difference between the chance of an event happening this year and the frequency with which it has happened in the past. Our initial forecasts are based on the UK Contingency Planners forecast: http://www.metoffice.gov.uk/publicsector/contingency-planners.
See the following links for more information: