They are the rarest and most dangerous of tornadoes and research shows Kansas has more of them than any other state. F5s.
Kansas has had 14 of the tornadoes at the top of the Fujita Scale, according to data compiled by severe-weather-research meteorologist Jon Davies of Kansas City.
Texas and Iowa share second place at 10 on the list, which dates back to 1880.
"I'm not sure people realize how statistically rare F4s and F5s are," said Mike Smith, president of WeatherData, a Wichita-based subsidiary of AccuWeather. "Out of every 1,000 tornadoes, roughly 50 are F4, and two or three are F5."
The fact that Kansas has had 14 F5 tornadoes is a reminder of why people in Kansas need to take tornado safety precautions seriously, weather officials say.
This is Severe Weather Awareness Week in Kansas. Officials say it's a perfect time for residents and businesses to join schools in reviewing and practicing what to do if tornadoes threaten.
The statewide tornado drill originally scheduled for today has been postponed because cloudy skies are expected in much of the state. The drill is now scheduled for 1:30 p.m. Thursday.
Given the Sunflower State's apparent vulnerability to the strongest of tornadoes, knowledge of proper safety measures is particularly important, weather officials say.
"Kansas has definitely had a lot of intense tornadoes," Davies said. "It's right in the middle of the Great Plains so it could get all the ingredients together to produce them."
But Harold Brooks, a research meteorologist with the National Severe Storms Laboratory in Norman, said no scientific reason explains why Kansas has had more F5s than, say, Oklahoma or Texas.
"There's also a little bit of luck involved," Brooks said in an e-mail. "Perhaps if we wait another 100 years, the answer will be different."
Davies created the list by merging F5s listed in the book "Significant Tornadoes 1880-1990" by The Tornado Project director Tom Grazulis with a database compiled by the National Climatic Data Center of the National Oceanic and Atmospheric Administration.
First on the list is a tornado that hit Harvey County on May 1, 1895, and killed eight people in or near Halstead and Newton. It ends with the Greensburg tornado of May 4, 2007, which killed 11 people.
The list doesn't include two tornadoes that almost certainly belong there, weather officials say.
The town of Irving in northeast Kansas was decimated by two tornadoes on the same night in May of 1879, the second of which may well have earned an F5 rating had the Fujita Scale been utilized at the time.
A wedge tornado that struck rural Cowley County on April 26, 1991, was rated F4 by Dick Elder, meteorologist-in-charge of the National Weather Service's Wichita branch.
In hindsight, Elder said last week, he should have rated that tornado an F5. It was one of the first damage assessment surveys based on the Fujita Scale, he said, and his parameters were basic.
An F4 will level a framed structure and leave the mess behind, he was told, while an F5 "cleans up after itself" _ carrying away the debris.
Because he found debris still on the scene of various locations in Cowley County, he rated that tornado an F4. Using the same criteria, he said, he also rated the 1991 Andover tornado an F4.
But a meteorologist who studied under Fujita did a flyover of the damage in the Wichita area, Elder said. When he learned the Andover tornado had carried an El Camino for more than a mile, the visiting meteorologist changed the rating to F5.
"In my opinion," Elder said, "the Cowley County storm was just as ferocious."
Officials caution that the tornado ratings are subjective. An Enhanced Fujita Scale introduced a few years ago is an attempt to remove as much subjectivity as possible.
Ratings of tornadoes more than 50 years old are typically at the mercy of whatever newspaper or eyewitness accounts happen to be available.
And because the Fujita Scale relies on damage to framed structures to calculate strength, any number of tornadoes in years past may have been as powerful as Andover or Greensburg but either weren't seen or didn't cause enough structural damage to earn an F5 rating.
Elder still thinks about a mile-wide wedge tornado that struck Sumner County on Memorial Day weekend in 1997.
"That was the biggest, largest, wedge F2 tornado that I ever did (an assessment on) in my entire life," he said.
Its rating was based on damage to the one house it struck. But he has no doubts it was much stronger than that earlier in its lifespan, he said.
Four of the seven F5s that have struck in Kansas since 1950 have occurred in the last 20 years, but meteorologists say that is a coincidence and not the reflection of a trend.
"The good news is, if you get an F4 or F5 today, it is extremely likely you'll have time to take cover," Smith said. "F4s and F5s usually create the strongest radar signatures, so there should be good warnings for them."
With well-established spotter networks and storm chasers swarming almost every strong thunderstorms, weather officials say, it's inconceivable that such large, deadly tornadoes could form and strike without warning.
When those warnings are issued, weather officials say, people need to pay heed.
"It's the perfect location on planet Earth for severe weather," Elder said.