I have family, (cousin in-laws), who lost their home and everything they own in Greensburg. Yes, there was about 30 minutes warning, which is unheard of--normally it is less than 5 minutes. The sirens are only located in town. Once you get outside the main part of the town and into the more rural areas of town, there is no warning. Also some of the houses were just flattened in place, trapping people either in their cellars or bathrooms, (normally the strong room in the house).
What is scary is that there are also parts of the US that have no warning sirens--Most of Florida does NOT have tornado warning systems. Most people have their own NOA warning systems.