The polar vortex has divided into two sections, allowing warm air from the northern Pacific ocean to extend into the Arctic, while displacing cold Arctic air south along the west coast. While the resulting forecast means that the east coast will see milder temperatures in the coming weeks, it also calls for colder than average temperatures in the west, and yet more above-average warmth in the Arctic, already suffering from record-low sea ice levels.
The polar vortex is a series of air currents that circle the poles, and in the north it typically isolates the cooler Arctic air mass from warmer mid-latitude air. However, over the last half of the twentieth century the vortex has been meandering south in an increasingly dramatic fashion, delivering cold Arctic air southward, causing persistent cold snaps in the affected regions over the past few years.
The current split of the polar vortex has occurred in the upper stratosphere, with the centers of both vortices pushing south, one down into western Canada, and the other into northern Siberia. While this will bring colder weather to the affected regions, including the western half of the US, the Arctic Ocean is caught in the middle with higher than normal temperatures. This has the potential to exacerbate sea ice melt, already having set a new record-low for the month of January.