The Polar Vortex Is About to Make Weather Weird From the UK to the US

The polar vortex is a band of upper-level winds wrapping around the Arctic Circle, acting like a dam to keep the season’s coldest air locked near the North Pole.

This circulation is usually strong and stable, but it occasionally weakens or reverses course, setting off an atmospheric chain reaction that allows bitterly cold air to spill southward.

The current disruption began on Tuesday and computer models expect it to last through Thursday, marking the earliest breakdown on record.

Historical Precedent

Disruptions of this extent typically don’t occur until the latter half of winter, making the current event highly unusual.

A highly disrupted polar vortex in early 2015 is a well-known example, sending a weeks-long burst of cold air sweeping over the eastern US, including Chicago and Lexington, Kentucky.

In that case, Chicago recorded its coldest February in nearly 140 years, and Lexington hit –18 degrees Fahrenheit.

Unprecedented Overlap

Weather patterns take a few weeks to respond to a polar vortex disruption, and reliable forecasts only extend about 10 days into the future.

While experts are still debating the exact causes, this breakdown throws another wrench into a cool season already dominated by the strongest El Niño on record.

Historically warm sea surface temperatures in the eastern Pacific Ocean have already significantly affected conditions around the world, and this influence will only grow heading into the winter months.

Much of North America can expect warmer-than-normal conditions during a winter dominated by a strong El Niño, but the vortex breakdown makes those forecasts less certain.