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Frequency of major sudden stratospheric warming events as of a function of (top) winter month and (bottom) winter season (November-March) since 1958. On average, there have been roughly 6 major events per decade since 1958. Some decades have had more than 6 while others have had less. Major sudden stratospheric warmings are most common in January and February. Only one major event has occurred in November. Statistics are based on ERA5 Reanalysis. NOAA Climate.gov image, adapted from original by Laura Ciasto.