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What’s stirring up this winter’s extreme storms?

Violent weather has battered the South and Midwest in recent days, bringing the death toll from up to 45. On Saturday, at least nine tornadoes swept through the Dallas area, blasting neighborhoods with winds of about 200 miles an hour. In other states, snow and ice caused power outages and heavy rain triggered deadly flooding. Jeffrey Brown talks to Bob Henson of Weather Underground.

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  • JEFFREY BROWN:

    The death toll rose to 44 today from violent weather that's battered the South and Midwest with tornadoes and floods since Wednesday. Some of the worst came Saturday, in Texas, in a barrage of deadly storms.

    Where there had been homes, shattered piles of sticks stretched across the North Texas landscape today. And survivors were still trying to tally their losses.

  • MAN:

    Oh, it's a big tornado, big, strong tornado.

  • JEFFREY BROWN:

    At least nine tornadoes swept through communities around Dallas on Saturday. They blasted some neighborhoods with winds of about 200 miles an hour and damaged or destroyed nearly 1,500 homes.

  • MAN:

    So, we all ran into the rooms to get into the closet and everything, and next thing I know, lights went out. Then the ceiling come off the house. Ceiling come off the house. And then it was gone, I mean, just like that. Just went through, tore up everything, went through.

  • JEFFREY BROWN:

    In neighboring Oklahoma, snow and ice punished the western and central parts of the state over the weekend, and up to a foot of rain hit the east.

    In all, some 175,000 customers lost power. Farther north, heavy rain triggered deadly flooding in Missouri. The victims included four soldiers from other countries temporarily stationed at a U.S. Army base. They died when they drove into a flooded roadway.

  • SHERIFF RONALD LONG, Pulaski County, Missouri:

    It's a small dark highway. It was raining very hard. It was 8:22. It was dark at nighttime. They probably did not know what hit them until they hit the water.

  • JEFFREY BROWN:

    In Southern Illinois, five more people drowned late Saturday when their car was swept away in a rain-swollen creek. The same storm system that generated that deadly weather kept moving today eastward across the nation's midsection. It brought snow and ice in parts of 11 states and more rain in places already waterlogged.

    The system forced more than 1,400 flight cancellations and another 2,600 delays. Extreme storms in the South and the Midwest — meanwhile, the east has been enjoying a practically tropical Christmas.

    Bob Henson is a meteorologist and blogger with Weather Underground, an online weather service owned by Weather.com.

    And, Bob, start with the tornadoes, if you would. How unusual, either in terms of the time of year or the number of them or their severity? What are you seeing?

  • BOB HENSON, Weather Underground:

    Well, it's not uncommon to get tornadoes in the South, including Texas, all through the wintertime. It's certainly possible. The strength of the tornado that hit in the Dallas area on Saturday is unusual.

    It was the strongest tornado ever to hit Texas in December. There have been tornadoes that strong in other parts of Texas in the South in December. But that was quite unusual. There was also some bad luck involved, because it happened to hit the eastern part of the Dallas-Fort Worth metro area, which is obviously one of the biggest cities in the country.

    And forecasters have long been afraid of what could happen if a tornado hit the DFW area head on. So, this was more of a glancing blow, but still, obviously, even that was pretty catastrophic.

  • JEFFREY BROWN:

    And are we better at — any better at predicting or mapping these things?

  • BOB HENSON:

    Absolutely.

    This was fairly well forecast in terms of tornado watches. And warnings were out as the storms moved in, so we certainly are better at capturing those. And I think indicative of that is the fact that something like 1,000 structures were damaged or destroyed, but the number of deaths was relatively small, although any death is too many.

  • JEFFREY BROWN:

    Now, a lot of crazy weather right now, records for warm weather. The warm weather is said to come from a variety of factors. Right?

    Tell us what we know about what is going on.

  • BOB HENSON:

    Well, it is a mix of things.

    One factor going on is El Nino, which tends to redistribute heat around the globe. It actually adds heat to the atmosphere by spreading more warm water over the eastern tropical Pacific Ocean. And that heat gets moved and shuffled around the globe. But there is also kind of a rearrangement of weather patterns. And sometimes that leads to warm weather, especially in the Midwest and Northeast in the wintertime.

    And December, in fact, during strong El Ninos, is known to have this effect over a large part of the Eastern U.S. So, we certainly saw that play out not just over Christmas, but the whole month of December has been amazingly mild. The Central part has yet to get below 32 degrees. It's by far the warmest December in most of the big East Coast cities on record, and in some cases going back to late 1800s, so an amazingly mild, moist air mass.

    And that actually also fueled the tornadoes in Texas and the flooding in the Midwest.

  • JEFFREY BROWN:

    And what do we know about the interaction, the impact between climate change and El Nino when it comes to looking at weather patterns right now?

  • BOB HENSON:

    Well, El Nino doesn't seem to be affected greatly by climate change in terms of frequency or duration or intensity, but one thing we know is that, in a warming atmosphere, the peaks of that warming tend to get expressed through El Ninos.

    El Ninos tend to warm the global atmosphere for a year or two. And La Nina, the counterpart, tends to cool the global atmosphere. So when you get a warming atmosphere, as we are with greenhouse gases, you can expect the warmest years to be the El Nino years.

    And we have one of the three strongest El Ninos in decades going on right now. So, from the perspective, it's not a total surprise that we're getting this warmth, not only in the U.S., but record warmth in Australia. And, in fact, Central England is having its warmest December in something like 350 years, so pretty impressive.

  • JEFFREY BROWN:

    And just briefly, what are you looking for in the next couple days, continuing severe weather in parts of the country?

  • BOB HENSON:

    Well, yes, the storm system is moving on through into the East.

    It's going to be settling down, I think, the next few days. And then we're going to see a bit of a realignment, with warmer weather, milder weather, I should say, across a lot of the West up into Western Canada, and perhaps some cold in the East through into January, parts of January.

    But El Nino does tend to force a lot of warmth across Eastern Canada and into Eastern U.S., Northeastern U.S. So I wouldn't be surprised if it's overall a pretty mild winter over North America. But we are always prone to those cold intrusions. And the last several winters have had some pretty sharp ones, as you know, in the Northeast.

  • JEFFREY BROWN:

    I will say. I will say.

  • BOB HENSON:

    And scientists are still trying to figure those out. So…

  • JEFFREY BROWN:

    All right, Bob Henson of the Weather Underground, thank you so much.

  • BOB HENSON:

    Thank you.

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