Microsoft’s bias-correction method improves two-to-six-week weather forecasts

Microsoft researchers and outside collaborators described Probabilistic Bias Correction (PBC) in a Nature paper published on 14 October 2026. It targets sub-seasonal forecasts, two to six weeks ahead, where physics-based and AI weather models both struggle. PBC takes an existing model, learns from its past forecasts where it tends to go wrong, and corrects its new forecasts.

Applied to the leading operational debiased sub-seasonal model, from the European Centre for Medium-Range Weather Forecasts (ECMWF), it improved 98% of precipitation, 92% of temperature and 91% of pressure targets. Microsoft says it also doubled the accuracy of ECMWF’s AI Forecasting System.

MicroDuet, a PBC-based entry from Microsoft researchers and outside collaborators, won ECMWF’s AI Weather Quest, a real-time competition. Over the competition’s first season it ranked first for every variable and lead time, ahead of six operational forecasting centres and 34 teams.

The Kenya Meteorological Service Authority is piloting PBC in the rainy season that began in October 2026, to judge the odds of very heavy or very light rain in its weekly forecasts. PBC is available as open-source software.