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KNOW IT ALL: Wednesday's Top 6 Stories at NBC News

From the blast of cold air hitting the South to fresh attacks launched by ISIS in northern Iraq, see the stories we're following.

Good morning, and happy Wednesday. Here are some of the stories we're following:

1. Get ready for potentially record-breaking subzero cold

Cold enough for you? A blast of arctic air dubbed the "Siberian Express" could shatter records and is set to leave millions of Americans shivering, particularly across the South, over the next few days. The bone-chilling temperatures could reach record lows in places such as Nashville, which could see minus-4 degrees (the record low was 5 degrees set in 1958) and Ashville, North Carolina, which could see minus-1 degree (the record low was 7 degrees also set in 1958). People in Arkansas through the Carolinas are also contending with power outages from the snow and ice storm this week that swept up the East Coast and dumped more snow on hard-hit Boston. Read more in NEWS.

2. ISIS launches fresh wave of attacks

ISIS attempted to overrun Iraqi towns southwest of Erbil, the Kurdish capital, on Tuesday night, but were repelled by reinforcements and airstrikes, sources said. The fighting was in close quarters as Kurdish forces eventually beat back the Islamist militants. A senior Iraqi security official said "tens" of ISIS fighters were killed and injured and some of their vehicles were destroyed during an hours-long battle that finally ended early Wednesday. Read more in NEWS.

3. Copenhagen shooter was in prison along with radicals

Prison radicalization has become a growing concern across Europe as law enforcement believe would-be terrorists are being groomed behind bars. Prison guards in Denmark fear Omar Abdelhamid Hussein, 22, was the latest case — he is the accused gunman who killed two people at a synagogue and a free speech event Saturday. Hussein had just been released from jail two weeks earlier after he was charged with stabbing a passenger on a train. Read more in NEWS.

4. Biden gets friendly at Defense Secretary's swearing-in ceremony

Vice President Joe Biden is known for his touchy-feely moments, and the latest episode can be added to the list. During the swearing-in ceremony for new Defense Secretary Ashton Carter, Biden beckoned Carter's wife from across the room and then put both his hands on her shoulders while Carter spoke. At one point, Biden whispered into her ear. The incident sparked prompt and voluminous reactions on social media, as many wondered: Just what was Biden thinking? Read more in POLITICS.

5. Las Vegas mom shot in road rage incident searched for suspect

The case of a Las Vegas mother of four who was fatally shot last week in a road rage incident took another turn Tuesday when police said she and her son were the ones who had gone looking for the male suspect. Previously, police had only said that Tammy Meyers, 44, was shot after returning home from teaching her teenage daughter how to drive last Thursday. But in new information, police said, Meyers arrived home after a run-in with the suspect and nudged her son, who was armed, to go out searching for him. Eventually, she returned home, and that's when the suspect followed them and fired his gun, hitting her, police said. Read more in NEWS.

6. West Virginia oil train derailment renews aging rail concerns

What caused a train carrying crude oil to derail in West Virginia on Tuesday, injuring one person and leaving a trail of smoldering wreckage? That's what state and federal investigators are trying to solve as the accident also raises questions about the nation's aging rail network. The train, owned by CSX Corporation, had been carrying oil from the Bakken Oil Fields in North Dakota to Virginia when it went off the rails near Mount Carbon. Read more in NEWS.

And now this ...

The top dog at the 139th annual Westminster Kennel Club Dog Show on Tuesday night was a beagle named Miss P. The best in show winner from British Columbia, Canada, strutted her stuff and wagged her tail for the excited audience. But there was plenty of fun behind the scenes as well.