Forecasting

A weather chart, a tool still utilised today despite the use of a hundred-trillion-calculations-a-second supercomputers

Creating forecasts — how we make them, why they're not always right and their role.

How we make a weather forecast

To make a forecast, we have to understand what the weather is doing now. To do this, we receive millions of observations from satellites, ships, aircraft, buoys, balloons, and weather stations covering the entire planet. This includes information from over the oceans, from the surface (ships and buoys), from high in the atmosphere (satellites) and below the oceans (a network of special floats called Argo).

All this information is beamed back to the Met Office headquarters and fed into our supercomputer. This high performance machine, capable of doing more than a hundred trillion calculations a second, takes this information as a starting point to run complex equations.

Comprising more than a million lines of code, the equations form a mathematical model designed to mirror the dynamics of the atmosphere. By putting current weather observations into the model, the computer generates simulations of what might happen next.

Output from the computer is then studied by experienced forecasters who look at a range of information to determine how accurate the simulations from the computer are. They add finer points to the forecasts before they are broadcast on television, radio and the internet, and delivered to a broad range of customers.

Why forecasts aren't always right

Our one-day weather forecasts are right six days out of seven, and today's four-day forecasts are as accurate as one-day forecasts were 30 years ago. While this shows great advances in reliability, we cannot always predict detailed differences in weather at a local level.

This is because the atmosphere is an extremely complicated system, affected by a huge number of factors and with the potential to react in endless different ways. To ensure completely accurate forecasts at all times, we would have to greatly increase the amount of observations we get so they cover every part of the planet, every minute of the day. Even then, a supercomputer far more powerful than anything in existence today would be needed to simultaneously process all this information into forecasts.

We are not there yet, but as we increase the number of observations, the complexity of the models, and the power of our supercomputers, forecasts should get more and more accurate.

Why the UK's weather is so difficult to forecast

It's all about location. The UK sits in between the Atlantic Ocean on one side and continental Europe on the other. This means even subtle changes in the wind direction can bring marked changes in the weather.

The UK also lies on the 'battleground' of warm air from the tropics and cold air from the Arctic, which collide to create numerous weather systems. This creates a highly active and volatile climate, which can see conditions change very quickly.

The role our forecasts play

Weather can affect our health, behaviour, and patterns of consumption. From how much power we use, to where and when we go on holiday, virtually everything we do can be influenced by the conditions outside.

Safety

Frost covered trees and a foggy road

Floods, stormy winds, heatwaves, cold weather and dense fog can all affect our safety. We provide alerts to the public on potentially dangerous weather through the National Severe Weather Warning Service (NSWWS). We also play a vital role in the Flood Forecasting Centre for England and Wales, set up in 2009.

Our Environment Monitoring and Response Centre (EMARC) provides advice when there is an incident involving chemical hazards, predicting where and how toxic fumes will spread and disperse. Similar services are provided for the spread of radioactive material, diseases and other airborne hazards.

Health

Weather affects our blood system, brain chemistry and some medical conditions. This has been proven by observed surges in demand for health services related to certain types of weather. We provide information to the Department of Health and various primary care trusts on how the weather will affect demand for services and bed space, helping them manage workloads. We also provide advice to people with certain medical conditions on when the weather may affect their health, helping them to stay fit, well and out of hospital.

Transport

Air, road and rail travel is affected by the weather and our forecasts help to keep people moving. This includes everything from giving detailed advice to highway maintenance workers on when to grit roads through our OpenRoad service, to our role as one of two World Area Forecast Centres (WAFC) providing flight forecasts for civil aviation.

Commerce

An electric pylon in a field

From high winds affecting construction work schedules, to when farmers should sow their crops, weather affects businesses in many ways. Importantly, it also affects consumer behaviour, having a significant effect on revenues for up to 70% of businesses. We provide a range of services to help the commercial world cope with the effects of the weather. These are essential for some industries, such as gas and electricity generation, storage and transmission, where our advance warnings help utility companies ensure there is enough supply to meet demand.

Air pollution

Weather can affect the level of pollution in the air, which can be a particular problem in cities - affecting comfort and health. We have models which predict the build up of atmospheric pollution and how long it will take for this to disperse.

Defence

We provide weather services to support British armed forces, both in the UK and abroad. Our expertise helps ensure the safety of servicemen and women, providing a range of support from giving information for military flights to advising on weather risks to troops on the ground, such as heat stress.

International

The Met Office has key international responsibilities, such as providing Emergency Response services and being a WAFC for aviation. As members of several international bodies, including the WMO, we also play an active role in sharing knowledge and working with experts from all over the world to improve weather and climate forecasting accuracy. This includes working on several multi-national projects as well as working with developing countries to help improve their meteorological services.

Climate change

The Met Office Hadley Centre is a world leader in climate science and research. Our work on climate change informs the UK and world governments, shaping key decisions on how to tackle the issues. To see more about what we do in this important area, visit our climate change centre.

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Last updated: 15 February 2013

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