The convection allowing models favor the idea of several storms near St. Louis and into the southern half of Illinois tomorrow. The NAM-12km says the CAPE could be up to 2000-3000 J/kg late in the day at 00z. The 500mb winds will be pretty strong, increasing into the nighttime, with over 40 kt of 0-6km shear, so I think there could be supercells. I would think tornado chances will be low due to weaker 850mb winds. The storms could move to southern Indiana and northern Kentucky, while riding along the faster 500mb-700mb winds.