Meteorological Synopsis
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.
On May 5, the SPC issued a high risk of severe weather for Central Kansas and central Nebraska, while moderate and slight risks for severe weather extended for areas far beyond. The low pressure system in place moved northward, but the extending front had barely moved. The storms were quick to develop. Severe weather reports were already coming in by late morning, and the first tornado reports came in during the early afternoon hours. The most intense activity took place during the late afternoon and evening hours as supercells developed along a long line from South Dakota to North Texas. Over 80 tornadoes were confirmed that day, along with hail as large as softballs and straight–line winds as strong as 90 mph (145 km/h). The activity weakened in the late evening, but not before the last tornadoes were reported in Iowa in the overnight hours.
The low gradually weakened and became less conducive for severe weather development on May 6. Nonetheless, the SPC issued a moderate risk for severe storms over parts of central Kansas and northern Oklahoma as the trough remained in place. The activity was far less than on the two previous days, however there were still several additional tornadoes across the Plains (all of them weak, mostly EF0). The system finally left the area on May 7 and did not produce any more significant severe weather.
Read more about this topic: May 2007 Tornado Outbreak