Table of major mid-winter SSWs 1958-2020

The date of the major warming is calculated for each reanalysis product using daily-mean zonal-mean zonal winds at 60N and 10 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar, where the winds must return to westerly for 20 consecutive days between events, and for at least 10 days prior to April 30, following Charlton and Polvani (2007).
The El NiñoEl Niño El Niño 'The Boy' is the warm phase of the El Niño–Southern Oscillation and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific-Southern Oscillation (ENSOENSO El Niño–Southern Oscillation is an irregular periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea temperature is known as El Niño and the cooling phase as La Niña.) phase (E = El Niño, L = La NiñaLa Niña La Niña is an oceanic and atmospheric phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation climate pattern. The name La Niña originates from Spanish for "the girl", by analogy to El Niño, meaning "the boy". In the past, it was also called an anti-El Niño[1] and El Viejo, meaning "the old man.", N = Neutral) is defined following the convention of the NOAA NCEP Climate Prediction Center, which is based on the DJFDJF Meteorological Winter comprising the months of December, January & February Oceanic Niño Index (ONIONI The Oceanic Niño Index (ONI) is NOAA's primary index for tracking the ocean part of ENSO, the El Niño-Southern Oscillation climate pattern.) using ERSSTv5 data with a +/-0.5C threshold.
The Quasi-Biennial Oscillation (QBOQBO The quasi-biennial oscillation (QBO) is a quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km per month until they are dissipated at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found.) phase (E = easterly, W = westerly) is defined using the DJF-mean equatorial QBO time series at 50 hPa from the Freie Universität Berlin.
The frequency of SSWsSSW A sudden stratospheric warming (SSW) is an event in which polar stratospheric temperatures rise by as much as 50 °C in the course of a few days. The warming is preceded by a slowing then reversal of the westerly winds in the stratospheric polar vortex. SSWs occur about six times per decade in the northern hemisphere, and about once every 20-30 years in the southern hemisphere. for each reanalysis is calculated for the 1958-2019 period for NCEPNCEP The United States National Centers for Environmental Prediction (NCEP) delivers national and global weather, water, climate and space weather guidance, forecasts, warnings and analyses to its Partners and External User Communities.-NCARNCAR The US National Center for Atmospheric Research is a US federally funded research and development center (FFRDC) managed by the nonprofit University Corporation for Atmospheric Research (UCAR) and funded by the National Science Foundation (NSF). and JRAJRA The Japan Meteorological Agency (JMA) is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation and research into natural phenomena in the fields of meteorology, hydrology, seismology and volcanology, among other related scientific fields. Its headquarters is located in Minato, Tokyo.-55; for the 1958-2002 period for ERAERA ERA stands for 'ECMWF Re-Analysis' and refers to a series of research projects at ECMWF which produced various datasets (ERA-Interim, ERA-40, etcetera).-40; for the 1979-2019 period for ERA-interim; and for the 1980-2019 period for MERRA-2.

I can’t see what the big fuss is about the chances of a change to very cold following an SSWSSW A sudden stratospheric warming (SSW) is an event in which polar stratospheric temperatures rise by as much as 50 °C in the course of a few days. The warming is preceded by a slowing then reversal of the westerly winds in the stratospheric polar vortex. SSWs occur about six times per decade in the northern hemisphere, and about once every 20-30 years in the southern hemisphere. event. More often or not CETCET Central England Temperature in the following weeks is completely unaffected. Here are some examples of SSW events in recent years.