Tornadoes can occur almost anywhere in the world, but the United States is the country with the highest frequency of tornadoes.
Each year there are about 1,200 tornadoes in the United States, causing about 65 fatalities and 1,500 injuries nationwide.
As of Friday, there had been 445 so far this year.
This is the fastest start for the first three months of the year since 1999, and it is in sharp contrast to last year when only 96 tornadoes had formed by April 3. Yet last year ended with exactly 1,200 twisters, according to NOAA. June was the busiest month in 2005.
Expect more: According to NOAA, "Previous years with a busy start have produced high numbers of tornadoes throughout the year." Abnormally warm temperatures and dry conditions during winter kept water temperatures warm in the Gulf of Mexico, the scientists say.
"Once a spring pattern developed in early March bringing weather systems eastward into the central United States, it combined with warm, moist air moving north from the Gulf, and created all the right ingredients for severe thunderstorms and tornadoes," Dan McCarthy, warning coordination meteorologist with the NOAA Storm Prediction Center in Norman, Okla. "If the pattern holds, the season could continue to be busy."
When and how they strike
In the United States, May has historically had the most tornadoes: 176 on average
Twisters often start to become a minor menace in March, depending on climate
Tornadoes form where warm moist air is trapped underneath a layer of cold,
If the conditions are right, the rapidly rising air
Although tornadoes are more frequent in the afternoon, they can happen anytime,
Tornado Alley
Twisters strike predominantly along Tornado Alley - a flat stretch of land
Texas gets hit the most, with an average of about 110 tornadoes a year. But
In 2005, scientists explained fresh twists on when and where tornadoes can strike, including in November in Ohio or in Michigan on an October night.
In southern states like Arkansas and Missouri, the peak of tornado season is
F-scale
In the early 1970s, T. Theodore Fujita developed a damage scale for high-wind
Violent tornadoes - F4 and above, with winds exceeding 207 mph - are less than one percent of all tornadoes,
Almost 90 percent of tornadoes are weak - F0 or F1 with winds below 113 mph - lasting usually less than
Memorable tornado events
- April 3-4, 1974: In 16 hours, 148 tornadoes were recorded across 13 states.
Staying safe
If a tornado strikes, the safest place is in a strong building - preferably
Mobile homes do not provide adequate protection from a tornado.
If there are no secure buildings nearby, lie flat with your hands over your
- Gallery: Tornadoes
- Tornado Science, Facts and History
- Fresh Twist on When, Where, Why Tornadoes Strike
- Hurricane Guide: Forecast, Science & History
- Gallery: Electric Earth
