Most supercells do not kill, and those that do kill rarely kill more than a few. The main threat for a supercell is the potential for tornadoes, and a supercell can produce multiple tornadoes in succession in what is called a tornado family, which can, in rare cases, kill dozens. In recent years one tornado family on April 27, 2011 killed 87 people in 3 killer tornadoes, and another on the same day killed 69 people in 6 tornadoes. On May 22, 2011 a supercell killed 158 people, all from a single tornado.
Yes, Spring Valley, IL, has tornado activity somewhat higher than elsewhere in the United States. The most recently recorded tornado occurred there in April, 2004. It was ranked as an F4 (violent, intense) tornado that killed 8 people, injured 12 people and caused $8 million in damages.
Those titles likely go to the followinThe Tri-State tornado outbreak of March 18, 1925. This outbreak produced a number of deadly tornadoes that claimed a total of 747 lives. Most of the deaths were the result of a single F5 tornado that track 219 miles across parts of Missouri, Illinois, and Indiana, killing 695 people.The Tupelo-Gainesville tornado outbreak of April 5-6, 1936. This outbreak was notable for producing two of the deadliest tornadoes in U.S. history only a day apart. The first tornado, an F5, struck Tupelo, Mississippi on April 5, killing at least 216 people. The second tornado struck Gainesville, Georgia on April 6, killing at least 203 people. With the added death tolls of several other killer tornadoes, this outbreak killed at least 454 people.The Palm Sunday Outbreak of March 28, 1920. Numerous violent tornadoes courred across the eastern third of the United States, killing at least 380 people.
It was definitely worse than the April 22-25, 2010 tornado outbreak. That outbreak resulted in 12 deaths, of which 10 were from tornadoes (one tornado actually). Preliminary reports indicate that the March 2, 2012 tornado outbreak killed at least 40 people. Hundreds are said to be injured. Damage is estimated at $1.5 billion. This outbreak is probably one of the worst outbreaks of recent history. The severity is comparable to the Super Tuesday outbreak of February 2008.
Note that deciding how dangerous a tornado is is very subjective. That being said, some good candidates to be considered among the most dangerous include:The Tri-State tornado of March 18, 1925. This tornado, the deadliest in U.S. tore across sections of Missouri, Illinois, and Indiana, killing 695 people as it destroyed town after town. The tornado was extremely powerful, an F5, capable of causing extreme damage. It moved at an average speed of 62 mph, and sometimes as fast as 73 mph, leaving little time to take cover. Additionally, the tornado was accompanied by a low cloud bases that made it hard to recognize and was often hidden by rain. This meant that many people did not know it was coming.The Hackleburg, Alabama tornado of April 27, 2011. This tornado was rather similar to the Tri-State tornado. It was an extremely violent EF5 (equivalent to F5) and moved quickly. For much of its duration it was obscured from view by rain. This tornado also hit multiple towns, of which Hackleburg was the first. Even with a modern warning system in place, this tornado killed 72 people, making it the deadliest in Alabama history and the deadliest in the U.S. since 1955.The Waco, Texas tornado of May 11, 1953. This F5 tornado was somewhat different from the Tri-State and Hackleburg tornadoes in that it did not move particularly fast. However, it was still completely shrouded in rain so that the people of Waco had no idea it was coming. A large section of Waco was leveled and 114 people were killed.The Jarrell, Texas tornado of May 27, 1997. This tornado was likely one of the most violent ever recorded. Unlike the previously listed tornadoes, this one was highly visible and very slow moving. However, the section of the town that was hit hardest was completely obliterated with every house, tree, and blade of grass blown away. Of the 27 people in the neighborhood, 26 died. One other person was killed on a nearby farm.The Smithville, Mississippi tornado of April 27, 2011. Like the Hackleburg tornado, which was on the ground at the same time, this tornado was rated EF5 and moved very quickly. What is notable about this storm, however, is how quickly it developed, reaching EF5 intensity less than two minutes after touching down, just before entering the small town of Smithville. Multiple homes and the town church were completely obliterated. A total of 16 people died in Smithville, followed by another 7 in Shottsville, Alabama. Had this tornado hit a larger population center the death toll would certainly have been higher.The Udall, Kansas tornado of May 25, 1955. This F5 tornado struck the unsuspecting town of Udall at night, when many people were asleep. The entire southern end of town was swept away and 80 people were killed.
10 people died on April 24, 2010 from a tornado in Mississippi.
The Andover tornado killed 17 people.
The five deadliest U.S. tornadoes of 2007 areThe Deland, Florida EF3 tornado of February 2 (13 deaths)The Greensburg, Kansas EF5 tornado of May 4 (11 deaths)The Enterprise, Alabama EF4 tornado of March 1 (9 deaths)The Lady Lake, Florida EF3 tornado of February 2 (8 deaths)The Eagle Pass, Texas EF3 tornado of April 24 (7 deaths)
The deadliest U.S. tornadoes in 2014 were:The Mayflows/Vilonia, Arkansas tornado of April 27, 16 deadThe Louisville, Mississippi tornado of April 28, 10 deadThe Smithfield, New York tornado of July 8, 4 deadThe Columbia, Mississippi tornado of December 23, 3 deadNo other U.S. tornado in 2014 killed more than 2 people.
On the date of April 26, 1989, the Bangladesh tornado killed 1300 people.
Like those in other months, most April tornadoes do not kill and most of the killers do not claim more than 1 or 2 lives. The deadliest tornado in world history, the Daulatpur-Saturia tornado in Bangladesh, struck on April 26, 1989, killing an estimated 1300 people. The deadliest tornado to hit the U.S. in April was the Tupelo, Mississippi tornado of April 5, 1936 which killed at least 216 people, making it the 4th deadliest in U.S. history. Two of the deadliest tornadoes in the U.S. in the era of modern forecasting were on April 27, 2011 and killed 64 and 72 people.
The Dallas tornado of April 2, 1957 killed 10.
The Tuscaloosa/Birmingham tornado of April 27, 2011 injured an estimated 1,500 people and killed 64.
The deadliest tornado in Oklahoma history was the Woodward tornado of April 9, 1947 with 181 deaths.
The largest tornado to hit Mississippi was the Yazoo City, Mississippi tornado of April 24, 2010. It was 1.75 miles wide.
The Daulatpur-Saturia tornado of April 26, 1989 killed an estimated 1,300 people.
The Daulatpur-Salturia tornado in Bangladesh. It occurred on April 26, 1989 and killed about 1300 people.