Storm Relative Helicity Values at 550 in South Illinois
Storm Relative Helicity at the 1 km level is determining the likelihood of rotation in the air 1 km from the ground. Increased potentials for tornadoes start at around 100 units, so 550 units in southern Illinois is quite a hefty indication that the atmosphere has some serious spinning motions going on.
I expect the highest values of the Storm Relative Helicity (SRH) to shift south as the cold front, denoted by the sharp gradient in east Oklahoma, moves east.
We will have more information on the developing potential outbreak as it comes along.