ECMWF's new long-range forecasting system SEAS5

Stockdale, Tim ; Johnson, Stephanie ; Ferranti, Laura ; Balmaseda, Magdalena ; Briceag, Simona

Année de publication
On 5 November 2017, the latest generation of ECMWF's seasonal forecasting system, SEAS5, became operational. As the name suggests, this is the fifth system we have run at ECMWF to produce real-time seasonal forecasts. Seasonal forecasts provide predictions of how the average atmospheric, ocean and land surface conditions over particular areas and periods of time are likely to be different from the long-term average. They are useful to a number of sectors, such as agriculture, water management, energy and health, and they can help to prepare for potential periods of extreme conditions. In SEAS5 a number of upgrades have been implemented, in particular in the ocean model, atmospheric resolution, and land surface initialisation. The new configuration also represents a move towards a seamless approach to forecasting across timescales. SEAS5 forecasts show substantial improvements in the tropics, in particular for sea-surface temperature in the equatorial Pacific. Unlike the configurations of ECMWF's Integrated Forecasting System (IFS) used to produce medium-range high-resolution and ensemble forecasts (HRES and ENS), which are typically upgraded at least once a year, SEAS is upgraded only occasionally, at intervals of four to six years. This slow refresh cycle is partly due to the resources needed to complete the large re-forecast sets required for calibration, and partly to offer users a more stable service. It is possible that this approach might change at some point in the future. We discuss the future evolution of seasonal forecasting at the end of this article.

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