Question: This may be a no brainer, but what makes tornadoes stop?

Answer: Tornadoes may dissipate because organized rotation is disrupted by winds that block inflow to the funnel, by loss of upward vertical velocities in the parent thunderstorm, from entrainment of cool, dry air near the surface that decreases instability in the storm, or by movement into an area where rough terrain or a change of surface type and temperature may upset the required balance of forces.