Significance Stratospheric ozone is one of the most delicate aspects of habitability on the planet. Removal of stratospheric ozone over the polar regions in winter/spring has established the vulnerability of ozone to halogen catalytic cycles. Elevated ClO concentrations engendered, in part, by heterogeneous catalytic conversion of inorganic chlorine to free radical form on ubiquitous sulfate−water aerosols, govern the rate of ozone removal. We report here observations of the frequency and depth of penetration of convectively injected water vapor into the stratosphere, triggered by severe storms that are specific to the central United States in summer, and model their effect on lower stratospheric ozone. This effect implies, with observed temperatures, increased risk of ozone loss over the Great Plains in summer.