An episode of anomalously low ozone concentrations in the stratosphere over northern Europe occurred on 3–5 November 2018. The 30 % reduction of the ozone layer was predicted by the global chemistry-transport model of the Finnish Meteorological Institute driven by weather forecasts of ECMWF. The reduction was subsequently observed by ozone monitoring satellites. The episode was caused by a storm in the northern Atlantic, which uplifted air from the troposphere to stratosphere.