May 2007 Tornado Outbreak

Tornado outbreak of May 4–6, 2007

Satellite perspective of the tornadic supercells over the Great Plains on the evening of May 5
Type	Extratropical cyclone Tornado outbreak
Duration	May 4–6, 2007
Tornadoes confirmed	129 confirmed
Max rating1	EF5 tornado
Duration of tornado outbreak2	56 hours, 9 minutes
Damage	$268 million
Casualties	14 deaths, 89 injuries
Areas affected	Great Plains, Central United States
1Most severe tornado damage; see Enhanced Fujita scale 2Time from first tornado to last tornado

¹Most severe tornado damage; see Enhanced Fujita scale

The tornado outbreak of May 4–6 2007 was a major and damaging tornado outbreak that significantly affected portions of the Central United States. The most destructive tornado in the outbreak occurred on the evening of May 4 in western Kansas, where about 95% of the city of Greensburg in Kiowa County was destroyed by an EF5 tornado, the first of such intensity since the 1999 Bridge Creek–Moore tornado. The supercell killed 13 people, including 11 in Greensburg and two from separate tornadoes. At least 60 people were injured in Greensburg alone. It was the strongest tornado of an outbreak which included several other tornadoes reported across Oklahoma, Colorado, Kansas and South Dakota that occurred on the same night.

Although the most damaging tornado of the outbreak sequence occurred in Greensburg on the 4th, only 25 tornadoes were confirmed that day. That number exploded to 84 the following day (May 5th), with many tornadoes near the affected area from the previous night. Most were in open country, but there were injuries in at least two spots in Kansas, and one death reported near a county lake in Ottawa County. 14 more tornadoes were confirmed on May 6th in the region before the outbreak finally ended.

It is the combination of warm humid air from the Gulf and dry air from the deserts of the Southwest that produce deadly storms. These conditions create an unstable severe storm creating arena. Although tornadoes occur on every continent except Antarctica they are especially common in North America, specifically the United States.

This severe weather outbreak can be traced back to a powerful, slow-moving low pressure area with a warm front to the north over Nebraska and Missouri. On May 4, the low stalled over the High Plains and additional moisture coming from the Gulf of Mexico moved in behind the warm front and increased amounts of instability across much of the region, with CAPE values as high as 5,500 J/kg. In addition, the dry line, which marks a divided line between the dry and humid air mass, was positioned over the southern High Plains. This allowed for the initiation of scattered supercells on May 4. High wind shear also allowed for intense rotation in the atmosphere. All the ingredients were present for the developing of supercell thunderstorms producing damaging wind, large hail and tornadoes.