Most tornadoes form in the U.S., although some events may take place internationally, particularly in parts of neighboring southern Canada during the Northern Hemisphere's summer season, as well as Europe.

One particular event, the Bridge Creek-Moore, Oklahoma F5 tornado, produced the highest wind speed ever recorded on Earth, which was 301 ± 20 mph (484 ± 32 km/h).

[5][6] Due in large part to this outbreak, Arkansas saw more tornadoes in 1999 than any other year, with 107 recorded, and its most active January.

The vast majority of tornadoes go unrated due to a lack of surveys; however, some nations, such as France, provide detailed reports on these events.

[5][8] The extreme activity during the month was attributed to an unusually spring-like setup, with a warm, moist air mass from the Gulf of Mexico flowing northward into an area with strong upper-level westerlies.

Ahead of this front, a strong low level jet formed, bringing a surge of warm, moist air from the Gulf northward.

The combination of these factors resulted in an unstable environment favoring the development of rotating supercell thunderstorms.

On January 18, a violent F4 tornado struck Mount Ayliff and Tabankulu in Eastern Cape, South Africa.

[16] The most notable tornadoes occurred on May 11 as multiple supercells developed along the cold front in Oklahoma and Texas.

Shortly after 6:00 p.m. CDT (2300 UTC), a 0.75 mi (1.21 km) wide multiple-vortex tornado struck Mason County, Texas.

Remaining on the ground for 7 mi (11 km), the F4 tornado cleanly swept away two homes and scattered debris over great distances.

[21][22]On May 15, a tornado struck rural areas of Suixi County, Guangdong, China, killing 13 people and causing extensive damage.

[28] More tornadoes, mostly rated F0, touched down on June 4, concentrating in two clusters; one in South Dakota and Nebraska and the other in Illinois.

[29] On June 5, a high risk for severe weather was issued for parts of South Dakota and Nebraska by the Storm Prediction Center as another violent tornado outbreak was expected.

[5][30][31] A supercell produced a tornado around San Quirino, Italy, causing damage to houses, sheds, and trees along a path width of about 300 m and length of less than 10 km.

[33] Other tornadoes also touched down that day across the Central United States, but the majority of them were short-lived and weak.

On August 8, Severe thunderstorms in Suffolk County, New York produced an F2 tornado which traveled from northern Mattituck, to Cutchogue.

[36] Touching down at 12:41 p.m. MDT (1841 UTC), the tornado quickly intensified as it moved through the metropolitan area for 4.3 mi (6.9 km).

The F2 tornado damaged or destroyed 300 structures, including the Delta Center and the city's capitol building.

Overall, one person was killed, 80 were injured, and losses amounted to $170 million,[37] making it the most destructive tornado in the state's history.

[39] In Pitkin County, Colorado, one storm produced winds up to 115 mph (185 km/h), downing hundreds of trees over a 3-square-mile (7.8 km2) area.

An extremely rare F0 tornado touched down in Pugwash, Nova Scotia, Canada.

Causing damage along a path at least 1 mi (1.6 km) long and 1,000 yd (910 m) wide, it moved through the impoverished neighborhood of Manenberg.

As Hurricane Floyd neared landfall in North Carolina, its outer bands spawned 17 tornadoes across the state.

A squall line originating in Illinois produced an F3 tornado in Pickaway County, Ohio, that destroyed several homes and injured six people.

[45] As Hurricane Irene neared landfall in Florida, it spawned four weak tornadoes across the state.

At an unknown point along the path, the tornado sucked up nearly all the water in a large shallow dam and deposited it on nearby hills.

A cold front moved into an unseasonably warm air mass over Pennsylvania, resulting in the formation of a tornado in Chester County.

Rated high-end F1, the tornado destroyed 6 structures and damaged 26 more, leaving $3 million in losses; 12 people were injured.