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A sudden stratospheric warming (SSW) is a large‐scale disturbance of the wintertime stratosphere, which occurs especially in the Northern Hemisphere. Earlier studies have shown that SSW occurrence depends on atmospheric internal factors and on solar activity. We examine SSW occurrence in northern winters 1957/1958–2016/2017, considering several factors that may affect the SSW occurrence: Quasi‐Biennial Oscillation (QBO), El Niño–Southern Oscillation (ENSO), geomagnetic activity, and solar radiation. We confirm the well‐known result that SSWs occur more often in easterly QBO phase than in westerly phase. We show that this difference depends on how the QBO phase is determined. We find that the difference in SSW occurrence between easterly and westerly QBO winters strengthens (weakens) if geomagnetic activity or solar activity is low (high), or if the ENSO is in a cold (warm) phase. In easterly QBO phase significantly more SSWs occur during low geomagnetic activity than high activity. Plain Language Summary: During some winters the cold polar stratosphere experiences a strong and sudden warming. These sudden stratospheric warmings (SSW) can affect greatly the surface weather in northern Europe and in North America. However, the factors that contribute to the formation of sudden warmings are not entirely known. We study how the two independent solar‐related factors, energetic particles and solar irradiance, and two atmospheric internal factors, the wind in the equatorial stratosphere (QBO) and the weather system of the Pacific (ENSO), affect the occurrence of sudden warmings in the Northern Hemisphere. We confirm the earlier finding that sudden stratospheric warmings are more common in winters with an easterly QBO wind. We find that the QBO effect on SSW occurrence depends on the two solar‐related factors and ENSO. Additionally, we find that the occurrence of sudden stratospheric warmings is affected by energetic particles precipitating to the Earth's atmosphere. Sudden warmings happen more often if the number of energetic particles is small. This effect is especially clear if the QBO wind is easterly. Our study helps to understand in which circumstances sudden stratospheric warmings are more or less likely to form. This information can benefit the forecasting of northern wintertime weather. Key Points: SSWs occur more often in QBO‐E than QBO‐W winters with the largest difference found if the QBO at 30 hPa of preceding autumn is usedQBO effect on SSW occurrence strengthens (weakens) if geomagnetic or sunspot activity is low (high) or if the ENSO is in cold (warm) phaseThe highest SSW occurrence rate is found in winters with low geomagnetic activity and easterly QBO [ABSTRACT FROM AUTHOR]