EDIT:

"In the early morning hours of May 27, a large mesoscale convective complex developed over Eastern Oklahoma and Western Arkansas. A "gravity wave" or outflow boundary was generated by this system and stalled out over Central Texas. This was oriented from the northeast to the southwest, causing the movement of the supercells later on to be to the southwest, along with most of the tornadoes, which is extremely unusual. Also unusual on this day was the low wind shear and extreme instability."
In the six-hour outbreak, there were 20 confirmed tornadoes including three F3s, one F4 and the Jarrell F5. And 28 deaths with the 27 in Jarrell and one in Lakeway (Travis County).
The Jarrell tornado was EXTREMELY violent - an entire subdivision was wiped off the earth, bodies were hard to distinguish between human and cattle, a huge amount of pavement was ripped from the earth, as much as 18-inches of vegetation and soil was pulled up, vehicles were pulverized into small bits (some known vehicles were never found), trees were debarked, etc. Some observers think that was one of the most violent tornadoes ever recorded.
And it happened on a non-classic kind of day.