ECMWF Newsletter #179

Longer ranges

Florence Rabier. Director-General.In addition to providing medium-range weather forecasts up to 15 days ahead, which is the main purpose of ECMWF, we have long produced extended-range forecasts up to 46 days ahead, and seasonal forecasts up to 13 months ahead. It is important to understand the applicability of such forecasts: they cannot produce the details of future weather conditions on a day-to-day basis, but they can provide projected deviations from average conditions over the weeks and months ahead. This makes them particularly useful to sectors such as agriculture, water management, energy and health, among others. Just as our medium-range forecasts are subject to continual improvement, so are longer-range forecasts. For example, in last year’s update of our Integrated Forecasting System (IFS) to Cycle 48r1, we substantially reorganised our extended-range forecasts: they now have 101 instead of 51 ensemble members, they run daily rather than twice-weekly, and they have a consistent horizontal resolution of 36 km. The seasonal forecasting system, which is currently SEAS5, is updated less frequently, at intervals of four to six years. The next system, SEAS6, is due to be introduced next year, and active preparations for this upgrade are under way.

An example of the use of our extended-range forecasts can be seen in this Newsletter, in the article on a cold winter in northern Europe. The fact that seasonal forecasts are the subject of continuous research becomes clear in the articles on improving the boundary forcing in reanalyses and seasonal forecasts, and in the feature article on a new time-varying tropospheric aerosol climatology for the IFS. The latter article also makes clear the intimate connections between ECMWF weather forecasts and the work carried out by the EU-funded Copernicus Atmosphere Monitoring Service (CAMS), implemented by ECMWF. It describes how a time-varying climatology will address two shortcomings: the current system is unable to represent changes in anthropogenic aerosols, and it is incompatible with the representation of aerosols in CAMS. There is also an article on the new Copernicus Interactive Climate Atlas, provided by the EU-funded Copernicus Climate Change Service (C3S) implemented by ECMWF. This includes climate projections from a range of sources.

Our cooperation with the World Meteorological Organization (WMO) is illustrated by an article on supporting the new WMO Incident Management System and by a report on a WMO fellowship recently completed at ECMWF. Additional feature articles describe recent updates related to ocean wind waves in ECMWF’s Earth system model, which will be implemented in IFS Cycle 49r1 later this year; they provide a detailed look at our forecasts of extreme rainstorms in Greece, Bulgaria, Türkiye and Libya in September 2023; and they present a new open-source Python development, called earthkit, providing powerful tools to speed up weather and climate science workflows. Overall, we aim for seamless predictions across the different forecasting ranges to maximise the usefulness of our products.

Florence Rabier