In today's newsletter: Investigators probe for a motive and potential accomplices in the New Orleans attack. A rush of arctic air is expected to hit the U.S. during the first few weeks of January. And NBC News went back to high school — with an Olympic gold medalist.

Here's what to know today.

A Texas man plowed a pickup truck flying an ISIS flag through New Year’s Day revelers on New Orleans' famous Bourbon Street, killing 15 and injuring more than 30 in an attack the FBI said is being investigated as an act of terrorism.

Once the driver, identified as U.S. citizen Shamsud-Din Jabbar, 42, crashed the white Ford truck around 3:15 a.m., he opened fire on responding police officers, wounding two of them. He died in the gunfight. “It was unbelievable,” Jimmy Cothran, who witnessed the attack from a nightclub balcony, told NBC News. “It just kept going.” He said he saw multiple bodies lying on the street within seconds, including many that were “horribly disfigured.”

Jabbar, an Army veteran and Deloitte employee, also had weapons and an improvised explosive device in the rented truck, the FBI said. There were other possible IEDs planted nearby in the French Quarter, two of which have been rendered safe.

Authorities are searching a site in Texas for clues about the suspect, and the FBI is working to determine his potential associations and affiliations with terrorist organizations. It is also investigating whether he had any accomplices.

Follow live updates here.

More coverage on the New Orleans attack:

Tesla Cybertruck bursts into flames outside Trump hotel in Las Vegas, killing one

A Tesla Cybertruck exploded just outside the entrance of the Trump International Hotel in Las Vegas, killing a person inside the vehicle and injuring several others standing nearby, local officials said.

The blast is being investigated as a possible terrorist attack, three senior law enforcement members briefed on the matter told NBC News. A motive has yet to be established.

Authorities are investigating a possible military connection between the New Orleans car-ramming suspect and the person who in the Cybertruck, two law enforcement sources familiar with the cases told NBC News. The pickup truck used in New Orleans and the Tesla in the Las Vegas explosion were rented from the same company, Turo, said officials.

The explosion was caused by fireworks or a bomb carried in the bed of the Cybertruck, Elon Musk said on X. Officials confirmed there were gasoline canisters and large fireworks mortars in the back of the vehicle.

U.S. braces for serious cold with a blast of Arctic air

A blast of Arctic air will send temperatures dropping across the Eastern United States this week — and the frigid conditions could linger longer and expose millions to a dangerous bout of winter weather. “We’re going to be stuck in a cooler pattern,” said Zachary Yack, a National Weather Service meteorologist based in Chicago. “It will definitely go into the middle and early part of next week.” The Arctic outbreak has already sent temperatures tumbling in the northern Plains states. Forecasters predicted Minneapolis’ high temperature would be 20 degrees Thursday and drop to 12 degrees Saturday.

Distortions in the jet stream will allow the cold air to stagnate and linger over much of the Eastern United States.

The Olympic gold medalist with high school homework to finish

When I attended the U.S. Olympic Trials in Eugene, Ore. last June, one runner stood out among the rest. No, I’m not talking about Noah Lyles, She’Carri Richardson or Gabby Thomas. I’m talking about Quincy Wilson, the 16-year-old who tore up the track in the 400-meter against men twice his age. After three blistering runs that week, he was chosen to compete in Paris on the 4x400 relay team. Though he didn’t run in the final, the squad earned gold — and so did Wilson, making him the youngest male Olympic track and field gold medalist in history.

But unlike his teammates, Wilson didn’t return home to train for a professional career. He still had two years left of high school. NBC News visited Wilson at Bullis School in suburban Washington D.C. to see how he balances classes and homework with being the best teenage runner in the country.

— Greg Rosenstein, sports editor

In the cold winter months, it’s important to keep your lips moisturized to avoid painful cracking and bleeding. These lip masks recommended by dermatologists and editors can help.

Thanks for reading the Morning Rundown. Today's newsletter was curated for you by Elizabeth Both.

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