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starting condition. This has enabled us to develop a range of probabilistic forecast products, which helps us to improve our forecasts about the risk of high-impact weather. This in turn benefits airports, through being better able to understand the uncertainty associated with any upcoming severe weather events and enables airports to manage their weather-related risks more effectively. Forecasting combines highly sophisticated technology with detailed meteorological knowledge of how the atmosphere, the earth’s surface and the oceans work. Modern weather forecasting applies scientific knowledge to predict future atmospheric conditions across the globe from observations of the current state - made over land, at sea, in the air and from space. Output from the model is used by meteorologists

to provide specific forecast services to the aviation community. The aim is to help minimise the impacts of the weather all year round although winter is a particularly challenging time for day to day operations


• One of only two World Area Forecast Centres (WAFC) providing high-level weather information for the entire globe • One of only nine Volcanic Ash Advisory Centres (VAAC) worldwide • Operates the SAtellite DIStribution (SADIS) system for commercial airlines and more than 120 countries.


• WeatherWindows: a planning tool allowing weather dependant tasks to be planned up to 15 days ahead, displaying the best time periods when tasks can be carried out. • ClearFlight: a global pre-flight briefing service for flight operators and dispatchers, which can be tailored to operators. Provides key weather information in one place enabling efficient flight planning, allowing users to monitor and stay abreast of situations such as volca- noes and storm tracks. Optional extras include inte- grated weather and flight-tracking plus NOTAM (Notice to Airmen) alerts • OpenRunway: a forecasting package to help keep runways open and running safely and smoothly. It ena- bles airports to plan effectively and keep one step ahead of changing weather conditions. • Aircraft De-icing: providing accurate forecasts of icing events up to five days ahead, to help reduce aircraft icing costs and delays through improved logistical plan- ning and more effective resource utilisation.

16 / AF /January 2014

at airports. Disruption due to winter weather puts a strain on schedules through delayed and diverted aircraft, causes significant inconvenience to passengers and impacts upon staff resourcing. Receiving the best weather information for destinations and departures gives airport operations teams the confidence to make critical decisions on diversions, aircraft and runway de-icing and justification for potential delays and the associated increased costs.

QUALITY OBSERVATIONS ARE VITAL Many UK airports have weather stations, which measure

a large variety of meteorological parameters, including air temperature; atmospheric pressure; rainfall; wind speed and direction; humidity; cloud height and visibility. Measurements are automatically logged at the weather station, which produces observations at one minute intervals. The data is then transmitted to a central collecting system where it is passed through stringent quality control checks. All observations are vital to the process of creating

forecasts and every day we receive around 500,000 observations - recording conditions around the world. Data sources are always changing and improving. They now include observations taken from more than 36,000km above the earth and from 2,000m below sea-level. Each day, all of these observations are used to create the starting conditions of our weather forecast model. However, even with so many observations we do not

have enough information to tell us what the atmosphere is doing at all points on and above the earth’s surface. There are large areas of ocean, inaccessible regions on land and remote levels in the atmosphere where we have very few, or no, observations. To fill in the ‘gaps’, we combine what observations we do have with forecasts of what we expect the conditions to be. This is a process called data assimilation and gives the best estimate of the current state of the atmosphere - the first step in producing a weather forecast.

Without data assimilation, any attempt to produce

reliable forecasts is almost certain to end in failure as even tiny changes in the atmospheric conditions can lead to drastically different weather patterns after only a short time. So it is vital the current state of the atmosphere is represented as accurately as possible, as from this, a forecast of how the future state of the atmosphere will evolve is calculated using a Numerical Weather Prediction (NWP) computer model.

A MATTER OF TIME Airports have many different requirements from

forecasts, not least whether the need is for a forecast of the

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