Abstract Deep convection that penetrates the tropopause (overshooting convection) transports water vapor and other tropospheric constituents to the upper troposphere and lower stratosphere (UTLS). Overshooting convection has chemical and radiative impacts on the UTLS, including the downward transport of ozone and hydration of the stratosphere. Currently, water vapor transport due to overshooting convection is not well quantified. In this study the Weather Research and Forecasting model (WRF) is used to simulate a Mesoscale Convective System (MCS) that formed on 9 June 2022 and produced multiple overshoots over the course of 12 hr, with radar echo tops reaching up to 5 km above the ERA5 tropopause. Observations from the NEXRAD radar system are used along with in situ aircraft measurements from the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) project to validate the simulated overshooting convection and horizontal transport of the water vapor plume. Isentropic back trajectories are used to match water vapor enhancements to individual overshoots and the mass of the plume is calculated by subtracting the stratospheric background. In total, the model estimates that this storm injected 121 kt of water vapor into the stratosphere: 56 kt into the 370–380 K layer, 30 kt into the 380–390 K layer, and 35 kt above 390 K with enhancements simulated as high as the 445 K isentrope.