Good evening. I'm William Brangham. John Yang is away. A fierce winter storm is barreling across the country,

with more than 70 million Americans under winter weather alerts tonight, and four million of those

facing blizzard conditions. At least six governors have declared states of emergencies.

Today, bitter cold winds whipped through the Great Plains and heavy snow-blanketed parts of the northeast.

The massive weather system will reach the Mid-Atlantic area later tonight.

In the coming days, it's expected to bring frigid temperatures as far south as Florida.

Matthew Capucci is a senior meteorologist at the MyRadar app.

Matthew, thank you so much for being here.

When you look at what is coming down now and what is forecast to come, what is it the most

concerning to you?

I think for me it's the fact that we're not seeing just snow.

It's the mix, the icy, wintry mix, the freezing rain and the sleet.

It's really complicating things.

You know, when we have freezing rain, it's difficult because that liquid initially washes

all the pre-treatment off the roadways, and so Cruz can't really get ahead of the game with

situations like this.

The other thing, too, is that behind this system, bitter cold Arctic air is infiltrating

the plains, spreading east across the Ohio

Valley. And so it's not just the fact that we're seeing power outages now, down the road,

if more people lose power, they'll be without any warmth for days on end.

Why is it that we're seeing? If it's this cold and this much snow coming down, why are we

also seeing rain in the midst of that?

...