Introduction
The three-month Outlook produced by the Met Office provides an indication of possible average temperature and rainfall conditions over the UK in the next three months. It is part of a suite of forecasts designed and produced on behalf of the Government for use by contingency planners and is one of several tools used in environmental risk planning by a number of different sectors. The three-month Outlook should not be used in isolation. It is recommended that this is used in conjunction with other information provided by the Met Office for the contingency planning community, including shorter-range forecasts (one-month, fifteen-day, and five-day) with more detailed information and weather warnings.
Background
Long-range outlooks are unlike weather forecasts for the next few days. The nature of our atmosphere is such that it is not possible to predict the precise weather for a particular day and place months ahead. At this longer-range, we have to acknowledge that many outcomes remain possible, even though only one can eventually occur. However, over the course of a whole season (or over a whole year or decade), factors in the global climate system (the atmosphere and oceans) may act to make some outcomes more likely than others. It is because of this that we can make long-range predictions, and the spread of possible outcomes provided in this outlook can be used to assess the likelihood and risk of particular events.
The skill of long-range outlooks varies with the time of year and with location, due to fundamental differences in how dependent local weather conditions are on global-scale atmospheric and oceanic processes at different times and in different regions of the world. Forecasts tend to be more skillful in the tropics than in mid-latitude regions. For example, our long-range forecasts are routinely used to predict inflow in water reservoirs in Africa. The UK is one of the most challenging regions for which to provide robust long-range information. This is because the weather in the UK is dominated by the atmospheric circulation over the North Atlantic which is highly variable and thus less predictable. In contrast, weather in the tropics is particularly dependent on slow variations of ocean conditions, such as El Niño, which are predictable months ahead.
The Met Office and our partners are continually improving all links in the forecast chain, from the model representation of key processes that affect UK weather to post-processing techniques that help decision-makers use all available information.