Multivariate ENSO index (MEI) is an index used to identify the atmospheric response of the sea surface temperature (and pressure) anomalies in the Pacific equatorial region. The 2023-24 El Nino episode, according to MEI, was the 3rd weakest (MEI = 0.68) since 1979 despite moderate to strong oceanic intensity using conventional Nino34 index.

Oceanic El Nino is weakening based on weekly Nino SSTA. However, atmospheric El Nino peak just occurred, based on a strong negative southern oscillation index. Indicated is El Nino climate may last a little longer than oceanic El Nino which is expected to shift to neutral phase during Q2/2024.

So far, during winter 2023-24 in North America, the prevailing climate is exceptionally mild across Canada and the Northern U.S. However, an 11-day period of hostile cold interrupted the warmth on Jan. 11-21 thanks to cross polar arctic airflow from Siberia. Similarly, Europe has observed a very mild winter season. There have been brief cold weather exceptions, one in early December and a second Jan. 7-14 featuring arctic air.

The convection phase of the Madden Julian oscillation (MJO) shifted to near and east of the Dateline in recent days intensifying moving across warm El Nino waters. The event caused southern oscillation index (SOI) to dip to the most El Nino-like signature of the 2023-24 episode. The MJO event and attendant strengthening EL Nino climate caused the California "bomb cyclone" of Feb. 4-5, 2024.