CNN 2011-04-29（在线收听）

…change, an egg roll, and an extraordinary talk show host. CNN Student News is back -- and so am I -- to bring you 10 minutes of commercial-free headlines from around the world.

First up, police in Poplar Bluff, Missouri are going door to door, telling people to get out. That's because of concerns about a levee on the Black River. Levees are barriers that are designed to prevent flooding. But according to an alert that went out yesterday from the National Weather Service, this levee "is weakening by the minute and may fail at any time."

It's another way that the state is suffering from the effects of severe weather. Poplar Bluff is about 130 miles south of St. Louis, and that's where this damage happened. Parts of St. Louis hammered by a tornado over the weekend. If you're in the path of a tornado, you've probably heard the big safety tips, which might include get in the basement if you're in a building that has one. Dan Simon is about to show you why.

This was the most destructive tornado of the season. This is what an F-4 twister looks like. That assessment was made, in part, by the damage you see here at this house and what you're seeing throughout the Harmon Estate subdivision, where we are in Missouri. I believe we're in the kitchen area, and the reason why I'm saying that is because we see that the refrigerator is right here.

In any event, the guy who lives here has had a really rough time. He actually works at the airport. He was there when the tornado struck. He and his colleagues hunkered down there. Then he got a phone call saying that maybe his home was destroyed. He drove here and this is what he saw.

And there's something I want to point out here, because this is worth showing here on camera. You know how they always say that you should go to the basement. This is exactly why you should go downstairs to the basement during a tornado, because while the upstairs is gone, the house is destroyed, the basement is basically intact. You have a little bit of the roof coming down here from the rain, but for the most part, this basement is intact.

The guy who lives here has a couple of dogs. The dogs actually took refuge in the basement and are OK. But here's why you should go to the basement during a tornado.

The U.S. government's updating its terrorism alert system to let Americans know about possible threats, and the new version goes into effect today. And you might be familiar with the old, color-coded system. It was put in place after the September 11th, 2001 terrorist attacks. There were five colors, from green through red that indicated risks from low to severe.

Under this new system, announced by Homeland Security Secretary Janet Napolitano last week, there will be two kinds of alerts: an elevated threat and an imminent threat. Napolitano said the goal of this change is to help people understand the threat better. That way they can know how to react. When she announced the new system last week, Secretary Napolitano said there is currently no threat that would qualify for either of the two new alert levels.