The U.S. arctic outbreaks in January and February were triggered by unconventional stratospheric warming events in that the warming was confined to Canada and the attendant polar vortex was locally generated, over North-central U.S. to cause the cold. Note that the stratosphere was cold on the Europe side of the North Pole. The March stratospheric warming event is stronger and across wider aerial coverage. However, the core of the warming is on the Siberia side of the North Pole therefore less reliably effective at generating North America cold.

A major severe weather outbreak is forecast for today across northern Gulf States and Mid-south U.S. A large area is forecast to receive tornado risk from Texarkana to Mobile today/tonight. On Wednesday, the severe weather risk shift is into the East. Tornado risk continues centered on the eastern Carolinas and southeast Virginia.

Of course, the explanation is complex. But, in my view, a large contribution to the unexpected cold pattern occurring mid-to-late meteorological winter across the U.S. was caused by the poleward latent heat release (caused by seasonality) across the record warm northern hemisphere oceans last mid-to-late autumn.

During recent weeks and particularly in February, the Nino3 SSTA region located in the eastern equatorial Pacific Ocean has warmed significantly while near the Dateline, La Nina cool waters persist. The difference between the two regions implies the 2024-25 La Nina episode has shifted west toward the Dateline implying formation of La Nina Modoki.