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.

Around February 17-18, temperatures are forecast to plummet to -40F to -50F in Siberia to Mongolia as rapid onset of an arctic air mass develops in response to stratospheric warming stretching from Siberia to the polar region and northwestern North America. Stratospheric warming enhances an evolving negative arctic oscillation (-AO) beginning later this week followed by emergence of a moderate to strong negative East Pacific oscillation (-EPO).

A potential third stratospheric warming event forecast for the middle third of February over Siberia to northwestern North America could spawn another arctic air mass. If the attendant negative arctic oscillation (-AO) is accompanied by negative East Pacific oscillation (-EPO) a North America polar vortex pattern could emerge especially if AO and EPO are in the -1.5 range as indicated for mid-month.