THORPEX: a Global Atmospheric Research Programme is an international research programme to accelerate improvements in the accuracy of 1 to 14-day high-impact weather forecasts for the benefit of society and the economy. The programme builds upon ongoing advances within the research and operational-forecasting communities. It will make progress by enhancing international collaboration between these communities and with users of forecast products.

he success of numerical weather prediction represents one of the most significant scientific, technological and societal achievements of the 20th century. Despite the notable increase in forecast skill over the past quarter century there is a necessity for further improvements, particularly, in high-impact weather forecasts and in the use of weather information. High-impact weather forecasts are defined by their effect on society and the economy. They are typically associated with forecasting cyclones of extratropical and tropical origin that contain significant embedded mesoscale weather, such as localized flooding by convective and orographic precipitation; blizzard snows; destructive surface winds; dust-storms. They also encompass meteorological conditions affecting air quality, periods of anomalous high/low temperature and drought, and non-extreme weather with high-societal impact. Improving the skill of high-impact weather forecasts is one of the great scientific and societal challenges of the 21st century. THORPEX is a response to this challenge.