Science Behind the News: Tornadoes

Air Date: 03/23/2012
Source:
NBC Learn
Creator:
Anne Thompson
Air/Publish Date:
03/23/2012
Event Date:
03/23/2012
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2012
Clip Length:
00:04:09

Tornadoes are violent, twisting columns of air with wind speeds over 100 miles per hour that can tear communities apart. Josh Wurman, an atmospheric scientist at the Center for Severe Weather Research, explains that tornadoes develop in a special type of thunderstorm called a supercell, but that there are still mysteries to unravel.

Science Behind the News: Tornadoes

BRIAN WILLIAMS (File Footage):

It was a worst-case scenario. Tornadoes, among the largest that nature can produce…

JIM CANTORE (File Footage):

The winds they estimated here were 170 miles per hour…"

LESTER HOLT (File Footage):

…a string of tornadoes, as many as 79, that touched down on Friday…"

ANNE THOMPSON, reporting: 

In late February and early March, 2012, two ferocious tornado outbreaks strike within days of each other. Nearly 80 tornadoes rip through parts of nine different states in the Midwest and southeast. At least 50 people are killed, hundreds more injured, and towns left in ruins.

ERIC GREGG (Harrisburg, Illinois Mayor) (File Footage): Hearts are broken. You know, knowing that we've lost children, we've lost loved ones, we've lost, you know, part of our family here in this community.

Dr. JOSHUA WURMAN (Center for Severe Weather Research): Most strong and violent tornadoes in the world happen in the United States. And most of them in the southeast, Midwest, and high plains in the United States, a region we call tornado alley.

THOMPSON: Josh Wurman is an atmospheric scientist and president of the Center for Severe Weather Research in Boulder, Colorado. With funding from the National Science Foundation, Wurman uses vehicles outfitted with radar and other special instruments to track tornadoes and unravel their mysteries.

WURMAN: If you want to see the fingerprints inside the tornado, we need to get close up, just like you would have to if you were taking a picture. If we get close up to a tornado, we can map out the winds. We can see all those small scale details.

THOMPSON: Most intense, violent tornadoes have their beginnings in severe thunderstorms known as supercells.

WURMAN: Supercell thunderstorms are defined by the fact that they are rotating. They have what's called a 'mesocyclone,' which is a rotating column of air that is about three or five miles across.

THOMPSON: While supercells can occur many places in the world, most occur in the central United States because of its unique geography and climate conditions during certain times of the year, when warm wet air move up from the Gulf of Mexico and encounters the strong winds of the jet stream.

These contrasting wind speeds and directions at different heights can cause a shift in the wind rotation of a thunderstorm, from spinning along a horizontal axis to twisting along a vertical one. This vertical rotation of air within the cell is a mesocyclone, an indication that a regular thunderstorm has become a supercell.

WURMAN: A super cell thunderstorm is a very complex animal. It has a very strong updraft. Winds could be moving upwards at a hundred miles per hour.

THOMPSON: Supercells also have strong downdrafts, and one of them, called a Rear Flank Downdraft, or RFD, is of particular interest to scientists.

They believe that as the RFD wraps around the mesocyclone and descends, it helps intensify rotation at the surface, causing a tornado...a twisting column of air extending below the supercell.

WURMAN: If you look at a radar image, you'll see this big hook coming out of the thunderstorm. And that hook is where the strongest rotation in the storm is, and that's where tornadoes form, if it's going to make a tornado.

THOMPSON: The goal of Wurman's research is to learn about these and other subtle differences in supercell thunderstorms that might help scientists forecast tornadoes more accurately and with fewer false alarms.

WURMAN: There's still a lot we need to learn. That's why we're still going out every year in these ambitious studies to try to peel back these mysteries, to try to understand more about what's inside these supercells that's causing it to make tornadoes when they do.

THOMPSON: With better forecasting and a better warning system, communities might be better prepared when the next tornado blows through town.

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