Amna Nawaz:

Judy, windchills in several states have already dropped, or soon will drop, to the negative 40s or 50s, which leaves people trying to understand what is behind this weather phenomenon.

Is there a connection between climate change and this cold front? And for some skeptics of climate change, it's providing new fuel for their disbelief. That includes President Trump, a skeptic not only of climate change, but also the scientific consensus behind it.

As the polar vortex set in earlier this week, the president tweeted: "What the hell is going on with global warming? Please come back fast. We need you."

Let's get a better understanding of what's behind the polar vortex, and any connection to climate change, with Jennifer Francis. She's a senior scientist at Woods Hole Research Center, well known for its work on the impact of climate change.

Dr. Francis, welcome to the "NewsHour." Thanks for making the time.

The polar vortex is now a trending hashtag on Twitter. A lot of people have a lot of questions.

Let's start with that. What exactly is the polar vortex, and why are we dealing with it right now?