Draft:2007 Greensburg Tornado

On the evening of May 4th, a powerful and deadly tornado struck the small city of Greensburg in Kiowa County, decimating the city and leading to the deaths of 11 people and injuring a further 63 people. It was a part of a tornado family that spawned 22 tornadoes and it was the strongest, costliest, and deadliest tornado of the family.

With the tornado being rated an EF5, it was the first tornado to be rated an EF5 using the newly made Enhanced Fujita scale, and the first tornado to be rated EF5 /F5 since the extremely violent 1999 Bridge Creek–Moore tornado seven years prior.

Meteorological synopsis


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.

The Storm Prediction Center issued a moderate risk for severe weather across western Kansas and small portions of Oklahoma, Colorado and Nebraska for May 4, while temperatures were in the mid to high 80s°F (near 30 °C). The atmosphere remained capped for much of the day, but storms began to develop in the late afternoon hours in western Oklahoma and the eastern Texas Panhandle. The most intense supercells developed in the early evening hours across northwestern Oklahoma and southwestern Kansas. They eventually produced 25 tornadoes, including the devastating Greensburg tornado and three other extremely large tornadoes which followed the Greensburg tornado late that evening. The supercells remained intact well into the overnight hours as the extremely unstable air mass precluded rapid dissipation expected with the loss of daytime heating which would normally be expected in the Plains. The last tornado of the night did not lift until shortly after 2:00 a.m. early on May 5.

Greensburg Supercell
Around the early evening hours of the 4th, The supercell that would eventually spawn the EF5 tornado would fire off at around 5:08 p.m. CDT, slowly organizing itself as it crossed into Kansas, soon the supercell would spawn its first tornado of the family east of Ashland, though it was weak and short-lived

The supercell would continue to produce weak and short-lived in Clark County and Comanche County in the rural farmlands of Kansas, including an EF1 that caused minor damage to a barn, before the supercell formed the EF5 Greensburg tornado.

Comanche County
The tornado would touchdown in northwestern Comanche County as a multi-vortex tornado traveling northeast through rural farmland as it gradually expanded in size as it would cross into Kiowa County. An EF1 satellite tornado from the main Greensburg tornado struck a few oil tanks and caused some tree damage, causing Oil to be scattered across the county road and across pastures.

Kiowa County
The tornado would cross into Kiowa County and multiple weather spotters reported a tornado half of a mile wide as it would spawn multiple satellite tornadoes, including one brief anti-cyclonic tornado. The tornado would could to expand in size as it continues its approach to Greensburg from the south before it reached its peak width at 1.7 miles (3000 yards), causing severe ground scouring and debarking trees, it also destroyed numerous farmsteads and killing livestock along Highway 183, with a confirmation that a massive wedge is on the ground heading towards a populated area and an intense velocity couplet showing on Doppler Radar, the National Weather Service would issue a tornado emergency for Greensburg and areas surrounding the city, at this point, the massive wedge was wider than the city of Greensburg itself.

The massive tornado continued north, entering a neighborhood in southern Greensburg, where multiple homes were swept clean off their foundations, Three of which were well-anchored homes. As a result, the damage for these three homes was rated EF5, ground scouring were also noted nearby. As the tornado continued its trek through the city, it slightly weakened to high-end EF4 as it entered residential areas in southern Greensburg, remaining violent, it struck the Delmar Day Elementary School, leveling one part of the building and numerous homes nearby the school flattened at EF4 intensity. Continuing north, downtown Greensburg was completely devastated by the tornado, numerous businesses destroyed. Two schools, a Tractor Supply Company store, the Greensburg City Hall, and many other businesses were destroyed. A motel on the western side of the town suffered severe damage, trees throughout the town were completely denuded and stripped clean of all bark, and vehicles were thrown hundreds of yards and mangled beyond recognition. The Greensburg water tower was completely demolished by the violent winds of the tornado, and the visitor's center at the Big Well was destroyed. Multiple train cars were overturned and hazardous materials teams were called to inspect the wreckage. A tank car carrying about 14,000 gallons (53,000 liters) of ammonia started to leak when workers lifted it. Numerous fire hydrants were torn off the ground in town as well. Greensburg High School would be another school that would get directly impacted by the tornado at high-end EF4 damage. One wing of the school was completely flattened, despite being well-built and constructed with triple-thick masonry walls. The tornado would restregthen back to an EF5 as numerous homes around the high school were swept away, four of the homes were properly anchored to their foundations. The Kiowa County Memorial Hospital was struck by the tornado at EF3 intensity, where 4.9-ton reinforced concrete beam were sheared off from the building. For the remainder of its path through Northern Greensburg, the tornado would continue to flatten homes and sweep many homes off their foundation, including a large brick Church that was flattened and had debris partially swept off the foundation, Trees would continue to be debarked and ground scouring would still be spotted.

Dissipation
After leaving Greenfield, the supercell was recycled and started to produce the Trousdale EF3 a few miles northeast of Greensburg as the original tornado started to weaken significantly and shrink in size as it started roping out northwest of Greensburg, finishing a loop before dying off completely.