Second polar vortex split in February of 2018 due to the Sudden Stratospheric Warming (SSW).
Less than two months after the December 2017 tropospheric polar vortex split, a phenomenon with a different mechanism occurred which resulted in formation of the familiar atmospheric configuration. This time it has been caused by an occasionally repeating event (usually by the end of a winter) - that of stratospheric sudden warming (SSW). The SSW origin is global: a huge amount of energy is lifted from the tropical deserts of northern Africa and Asia and then catapulted over the tropopause towards the North Pole. After a few days of northbound travel the energy pulse hits the stratospheric polar vortex like a projectile either pushing it away from the North Pole or splitting it in two. The mechanism is explained in detail in the chapter: THE MECHANISM OF THE HUNDRED-THOUSAND YEAR CLIMATE OSCILLATION (paragraph C). Just like over several most recent winter seasons also this time the polar vortex split into two well-formed halves and, similarly, the centers of both located themselves in the same, familiar, spots: the American one slightly east of the Hudson Bay, and the Asian one in the area east of Ural mountains. These two spots are traditionally the coldest places of both continental land masses. As the result of the SSW the North Pole undergoes very rapid warming; there is no doubt the reason both vortices move to these two locations as they both ensure the lowest gradient of temperatures. Any polar vortex (single or double) will always tend to locate itself in the spot where the temperature of its environment is the lowest.
Simultaneous Pacific and Atlantic omega blocking leading to a polar vortex split of the tropospheric origin
So, within only 7 weeks there have been two polar vortex splits in the same winter. Although caused by two different atmospheric phenomena, such frequency quite possibly happened for the first time ever. The fact alone that polar vortex split happened twice within one winter may actually be characteristic of the development of the overall climatic conditions that will propagate polar vortex splitting in future leading to a permanent dual polar vortex configuration which is the steady, normal condition of the northern hemisphere in an ice age. If the contemporary world climate does really change, (it’s a tabloid cliché these days although nobody has really proven it yet) then the change might be really towards those new, ice age characteristic atmospheric configuration. In this situation then, the climate change might as well be a herald of the return of the ice age, especially because it all happens just before the end of the 12th millennium of this current interglacial. As the polar vortex split happened twice in the course of this winter (separated by a short time interval) one question that might be asked is what would have happened if both phenomena occurred simultaneously. If multiple splitting of the polar vortex will continue to happen within one winter then sooner or later both phenomena will overlap for certain.
Looking at a series of images (above), presenting the tropospheric polar vortex split of late December 2017 it can be observed how deep into the polar area each of the blockings invaded. It would not take much more for both of them to meet right above the North Pole. It did not happen, though, so the cross polar air flow was still able to wander from Siberia to North America. Such flow helped to maintain the North Pole area relatively cool and, as the consequence, to keep both polar vortices relatively close to its vicinity. Let us now imagine the SSW also happened exactly at the same time (it could, as both phenomena are of completely different origin, not dependent one on another). Sudden warming of the North Pole would cut off the "Siberian Train", a streak of frigid air from continental Asia with the consequence of the opening the "Trans-oceanic Train", this time of exceptionally warm air. The consequence could be very serious. Such flow would make the North Pole balmy and in the search of a colder environment (lower temperature gradient) both polar vortices would move even further south to freeze over not only the Great Lakes and northern part of the East Coast but also the central and southern areas of the USA. As those super cold air masses would meet the moist ones of the south, the snow fall there could be catastrophic. The situation would bear most of the characteristics of the dreaded Sudden Cooling Event discussed in the chapter Interglacial End (A). The situation would eventually come back to normal after a few days again, no doubt, but the event would give a bitter fore taste of the oncoming Ice Age.
SSW of Feb 2018 that caused the polar vortex to split
Z.D. Lawrence animation of the February 2018 polar vortex split.