AP News, March 2nd, 2007
The violent storms that claimed lives in the Midwest and Southeast are part of an annual pummeling that sees an average of 1,000 tornadoes hit the United States. So far this year, there have been more than 150 twister reports.
Some questions about tornadoes with answers compiled from the National Climatic Data Center, National Weather Service and Storm Prediction Center of the National Oceanic and Atmospheric Administration.
Q. Is it early in the season for tornadoes to occur?
A. Not really. National Weather Service meteorologist Dennis Feltgen reports twisters can occur in any month. Early in the year they tend to occur more often in Florida and the Gulf Coast, shifting to the Southeast region in March and April and into the Plains later in the summer.
Q. How many were there in this outbreak?
A. There were 31 reported on Thursday. So far this year there have been 29 tornado reports in January and 89 in February.
Q. Several people were killed in the outbreak, were they the first tornado deaths this year?
A. No. There were 2 tornado deaths in January and 21 in February, most when storms and tornadoes cut across Florida.
Q. How many deaths occur from tornadoes in an average year?
A. It varies a lot from year to year but the average is about 60 deaths.
Q. What was the deadliest tornado?
A. There were 695 people killed in the Tri-State Tornado that swept across Missouri, Illinois and Indiana on March 18, 1925. The Super Outbreak occurred on April 3-4, 1974, when 315 people died in some 145 tornadoes that battered Ohio, Indiana, Illinois, Kentucky, Tennessee, Alabama, Georgia, Virginia and West Virginia.
Q. What is the record month for tornadoes?
A. May 2003 holds the record with 543 tornadoes confirmed.
Q. Has the number of tornadoes been increasing?
A. It's hard to say. More are being reported, but in past years many might have occurred in unpopulated areas or were simply not reported if they did little or no damage. Today the popularity of video cameras and computers means twisters tend to get recorded and reported more readily.
Q. What is Tornado Alley?
A. It's a popular nickname for an area of relatively high tornado occurrence in the central U.S. There is no official definition.
Q. Does El Nino cause tornadoes?
A. The Storm Prediction Center says El Ninos and La Ninas _ changes in sea surface temperature in the tropical Pacific _ adjust large-scale weather patterns. "But in between those and tornadoes, there are way too many variables to say conclusively what role El Nino or La Nina has ... and it certainly does not directly cause tornadoes."
Q. So, what does cause them?
A. The traditional answer is "warm moist Gulf air meets cold Canadian air and dry air from the Rockies," but it's really more complicated than that. Tornadoes occur in strong storms called supercell thunderstorms that have rotating updrafts caused by the differences in wind direction at different heights in the atmosphere. That's call wind shear. The storm downdraft also rotates and from this process the tornado develops.
Q. Is that what happened Thursday.
A. Absolutely, says Feltgen. There was a major winter storm in the Plains and inflowing warm, humid air from the south and southwest. High above, a powerful jet stream was blowing from the west at more than 150 mph allowing the thunderstorms to develop into supercell storms. "These are the type of storms which can and do produce these strong and violent long-lived and long-track tornadoes," he said.
Q. Were there warnings issued?
A. The Weather Service outlook for the day was for a high risk of severe weather. A tornado watch was issued early in the day citing a "particularly dangerous situation" with strong to violent tornadoes possible.
___
On the Net:
National Oceanic and Atmospheric Administration: http://www.noaa.gov
National Weather Service: http://www.weather.gov
