From the National Weather Service in St. Louis:
Thunderstorms are expected Saturday afternoon and evening. While timing is shifting slightly from run-to-run, the forecast models have been very consistent in forecasting conditions which can produce severe thunderstorms. It is likely that some of these thunderstorms will become severe particularly along and south of I-70. Large hail, damaging wind gusts and tornadoes will be possible. Make sure you are Weather Ready and have a plan of action in place if warning is issued for your location this Memorial Weekend.