Columbia and Boone County are included in a tornado watch the National Weather Service in St. Louis issued Wednesday afternoon.
The watch means conditions are favorable for the formation of tornadoes. It began at 2:12 p.m. Wednesday and was scheduled to remain in effect until 9 p.m.
Twenty-four counties in east and central Missouri are included in the watch. Those include Cole, Audrain, Callaway and Moniteau counties.
The weather service said strong convection in the atmosphere presents the threat of strong to severe thunderstorms with damaging wind and hail. It said the primary threat would be to counties in eastern Missouri and southern Illinois as a front moves southeastward.
"A prolonged and dangerous heat wave" also is expected from Friday through Tuesday, with heat indices each day between 100 and 110 degrees.