We are still in the process of collecting and developing ways of studying and analysing air traffic routes across the North Atlantic. The results presented in this paper must therefore be recognized as provisional. The data comprise some twelve examples of North Atlantic weather forecasts issued from Bracknell; they are sent to us regularly for the 2nd and 15th day of each month. We have also made arrangements to receive notification from the Heathrow Meteorological Office of any days in which there were significant changes in the weather forecast, so that we can request the additional information from Bracknell. Each set of weather data contains the ‘analysis weather’, that is the best estimate of the actual weather at 1200 GMT, and therefore applicable to the time when aircraft are making westerly departures across the North Atlantic from European cities, and also the weather forecasts issued for 12 and 24 hours before this time.